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This PDF file contains the front matter associated with SPIE Proceedings Volume 1514, including the Title Page, Copyright information, Table of Contents, and Conference Committee listing.
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Millimeter Wave Extended Interaction Klystrons manufactured by Varian Canada Inc., since 1969 utilize rectangular resonant cavities with a biperiodic ladder as the interaction circuit. These klystrons are used in radars, communications, scientific instrumentation in the frequency range of 28 to 280 GHz at peak power levels from 1 kW to 5 W, average power levels from 1 kW to 0.5 W . To facilitate the use of these klystrons, power conditioners were introduced in 1983 to combine with the klystrons to form pulsed or CW transmitter subsystems.
In this paper, elementary theory of operation of the EIKs is described, together with design considerations and system interface information. Some historical milestone achievements of the EIK transmitters are summarized. Recent advances are presented, including frequency coverage, output power, bandwidth, gain, noise, size, weight, efficiency, and pulse repetition frequency. Future development of these products are discussed.
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We have designed and tested two types of the auto-resonant peniotron oscillator (ARPO), one with a magnetron type cavity and the other with a quadupole circuit cavity. In this report we present their design and the preliminary test results.
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Microwave surface impedance data at 87GHz of epitaxially grown thin films of YBa2Cu3O7-δ prepared in situ by excimer laser ablation, dc sputtering, and thermal coevaporation on SrTiO3, MgO, and LaAlO3 are compared. At 77K the lowest surface resistance values were achieved with laser ablated films on SrTiO3. At 4.2 K and low field levels for all preparation techniques and all substrates nearly the same anomalous high residual surface resistance values occur. Both the microwave and the far infrared reflectivity data at 4.2K are described consistently within the two fluid model indicating a large amount of remaining normal conducting charge carriers.
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The response of poly crystalline Tl-Ba-Ca-Cu-0 superconducting thin films on short laser pulses has been investigated for radiation between 10 μm and 500 μm wavelength. Fast signals with time constants less than 1 ns were observed for wavelengths longer than about 100 μm whereas for shorter wavelengths only a bolometric signal could be detected.
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A Nernst effect has been observed by a laser heating method in a Tl-Ba-Ca-Cu-0 superconducting film. The film was irradiated with radiation pulses of a TEA-CO2 laser inducing a temperature gradient perpendicular to the film surface. In a magnetic field parallel to the film surface a Nernst voltage was observed perpendicular to both the temperature gradient and the magnetic field. We have investigated the Nernst voltage in dependence of sample temperature and magnetic field and find, from an analysis based on thermal activation of flux tubes, a distribution of activation energies ranging from 100 K to 4000 K in our samples.
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In this paper we study the room temperature infrared transmission spectra (400-1800cm-1) and far-infrared diffuse reflection spectra (50-450cm-1) of Pb-doped Bi-Sr- Ca-Cu-0 single phase (Tc=107k),multiphase (Tc=110k) and nonsuperconducting samples.There are seven absorption bands in the 400-1800cm-1 and eight diffuse reflection bands in the 50-450cm-1 region in superconducting system.The Cu-0 stretching vibration (605cm-1) and Sr-0 vibration (254cm-1) may be the characteristic peaks in Bi-based family.
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EPR measurements at microwave and far-infrared frequencies on Gd-spins in powders of Bi2Sr2Ca1-xGdxCu2O8+y and GdBa2Cu3O7-d reveal a marked increase in linewidth at low temperatures. This cannot be fully accounted for in terms of crystal field split ting, dipolar broadening and inhomogeneous demagnetization. It is argued that a large contribution can come from interactions of the Gd-spins with antiferromagnetic excitations in the CuO-planes.
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Using the backward wave oscillator measurement technique (submillimeter BWO "Epsilon" spectrometer, 3-33 cm-1 we have studied the electrodynamic properties (permittivity ε’ and dynamic conductivity σ) of a number of Y-, La-, Bi-based high-Tc superconductors (ceramics, thin films), nonsuperconducting parent La2CuO4 single crystal and substrates for high -Tc superconducting films (SrTiO3, MgO, SiO2, AI2O3, Zr02+Y203, HfO2+Y203, Si, GaAs, TiO2, LaGaO3, MgF2, CaNdA1O4, SrLaA1O4, BaLaGa3O7, SrLaGa3O7).
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A cooled HEMT low-noise amplifier has been designed for a submillimeter heterodyne balloon-borne receiver working at an intermediate frequency of 6 GHz. A minimum noise temperature of 16 K has been achieved at a cryogenic temperature of 27 K. Different methods for an accurate noise figure measurement in a cryogenic environment will be discussed.
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A stressed Ge:Ga photoconductor array with 3 elements has been developed for the Infrared Telescope in Space (IRTS) satellite of Japan. The detectivity was very high at low temperature and under low infrared background. Nonlinear response dependent on photon influx was observed in the experiments and the phenomenon is discussed in the paper.
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An infrared camera with a HgCdTe 128X128 array has been constructed for ground based astronomical observations. The camera has a wide field of view of 4.2’x4.2' at the 1.5 m-telescope of the Communications Research Laboratory (CRL), and it is a powerful instrument for observing extended objects like galaxies.
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A new 34-m millimeter wave telescope was built at Kashima Space Research Center(KSRC), Communications Research Laboratory(CRL). The millimeter wave VLBI(Very Long Baseline Interferometry) experiment called KNIFE (Kashima-Nobeyama Interferometer) had started at 1989. The present status of the telescope and the first result of the 43GHz VLBI experiment are reported.
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A submillimeter balloon-borne receiver, including a 380 GHz cryogenic Schottky diode mixer with 6 GHz IF, has been investigated. At room temperature, 1400 K DSB mixer noise temperature has been achieved; cooling down the device should allow a strong increase in receiver sensitivity.
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The present paper reports the measured frequency stability of a compound quasi-optical power combiner. The frequency stability of the quasi-optical power combiner consisting of Fabry-Perot cavity and two rectangular least 10- 5.
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We have introduced secondary-mirror chopping in our balloon-borne far-infrared 60 cm telescope equipped with He-cooled filters and a composite silicon bolometer with an NEP of 1.3-10-14 W/Hz1/2 for imaging, radiometry and spectroscopy of the Cygnus region at the wavelengths 80 μm, 125 μm and 330 μm. We also report on the flight scheduled for Sept. 1990.
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The availability of power for use in space is a key requirement for many future space activities. The use of microwave/millimeter-wave power transmission in space provides an alternative energy generation and delivery system. Three - phase experiments on board the space shuttle are proposed to demonstrate the feasibility of microwave power transmission in space.
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The grating-coupled oscillator is an electron-beam-driven grating-loaded quasi-optical resonator. Devices such as the Orotron/Ledatron, in which a spherical mirror is placed on an axis that is normal to the grating, fall into this category.
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The Vacuum Electronics Branch of the Naval Research Laboratory has an ongoing program to evaluate the potential of the ubitron/FEL interaction as a high-gain, high-power, broad bandwidth micro- or millimeter wave source. Moderate gain operation of the NRL ubitron has been previously reported using a modified SLAC klystron gun. An improvement in the gain has been observed following the installation of a higher current, higher quality electron gun. The maximum gain for a uniform axial field is 20 dB, and substantial gain has been measured over the 12.6 to 17.4 GHz frequency range. Gain is found to be limited by the onset of a high-power oscillation. The oscillation can reach high power levels (⇔ 700 kW) and is dependent on the wiggler field. In addition, it exhibits oscillation thresholds dependent upon both beam voltage and wigglevelocity. The power is also dependent on the axial field profile, and the trim coil current. Both amplifier and oscillator experimental measurements are compared with a fully three-dimensional nonlinear simulation of this configuration using the code ARACHNE.
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A 1 MW (cw), millimeter wave FEL (λ3 ≈ 0.5 mm) is currently under development with an application for heating fusion plasmas. Two salient features of the FEL are the use of a short-period wiggler ≤ 10 mm) electromagnet and a mildly relativistic (Ebeam ≤ 1 MeV) sheet electron beam. The FEL has been designed to operate in the highgain regime and uses a tapered wiggler. The wiggler provides beam focusing as well as the magnetostatic pump wave. The effectiveness of wiggler focusing is being investigated. Planned experiments will address the critical issues of beam interception and stable single-mode operation.
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Experimental measurements of high power microwave generation from an electron beam passing through a high-Q Bragg resonator have been performed using the long-pulse accelerator, MELBA. We have fabricated a high-Q sinusoidal Bragg resonator to study a high frequency CARM oscillator designed for operation on the TE31 mode at 18.9 GHz and the TE4 1 mode at 20.5 GHz. A diffraction Q ~ 16,600 is consistent with the prediction of uncoupled single mode theory. A high quality annular electron beam of 30 - 80 amps is produced through 80 small holes in an apcrtured-mask-anode. The beam velocity ratio, α = ..., was directly measured by Cerenkov emission and radiation darkening on a glass plate diagnostic and agreed with calculations from Busch's theorem and an electron trajectory code. In preliminary results with the Bragg resonator, the peak full band (f < 14 GHz) power was in the range (0.6 - 1.2 MW); in the frequency band from 18.7 - 19.2 GHz (includes the TE31 Bragg mode) the power was 15 dB less. Without the Bragg resonator (smooth tube) the peak full band power was 0.1 - 0.3 MW; the peak power in the band from 18.7 - 19.2 GHz was approximately equal to the full band power. Mode identification studies are underway, as fundamental and harmonic gyrotron interactions are believed to be a strong source of mode competition in the present experiments. Efficient, multi-megawatt microwave emission in the band 2.1 - 6.6 GHz is believed to originate from a TE11-fundamental-mode gyrotron backward-wave-oscillation (gyro-BWO) in the Bragg resonator case.
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A proof-of-principle experiment has been designed to examine harmonic operation of the ubitron/free electron laser (FEL) interaction
mechanism in an amplifier configuration at low voltages. Harmonics are a key in reducing the high voltage requirements of ubitrons.
The configuration of the experiment consists of a 250kV/100A electron gun, an input transition from single mode to overmoded
waveguide, a linear wiggler, mode selective output couplers, and a calorimeter/water load.The experiment has been assembled and
initial operation is underway. Details of the final experimental design are presented along with results to date on propagation of the
electron beam through the meter long linear wiggler.
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Reported here is the experimental evidence for the generation of pulsed micro- and millimeter wave radiation in the range of 20 to above 100 GHz from a back-lighted thyratron (BLT) or pseudospark. The device is simple, robust and supports both an intense, low-emittance electron beam and a high-density, glow-mode plasma.
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A new kind of compound quasi-optical power combiner is presented. It consists of two single waveguide cavity multipledevice power combiners and a Fabry-Perot cavity, and shows characteristics of both single waveguide cavity multi-device power combiner and quasi-optical power combiner.
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Requirements for spaceborne spectrometers are presented. Also, characteristics of an Acousto Optic and a Digital Autocorrelator spectrometer being developed for spaceborne mm-wave radiometers are given.
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The 3246th Test Wing (TFIM) at Eglin AFB, FL, and the Georgia Tech Research Institute (GTRI) at Atlanta, GA, are jointly developing a 95 GHz instrumentation radar system to be used in the collection of terrain (clutter) backscatter signatures as well as target-in-clutter signatures. The system will address the research and development, test and evaluation (RDT&E) data requirements for a variety of US Air Force and US Army smart weapons systems to include data required for modeling and analysis, hardware-in-the-loop simulators, and coincidental sensor/seeker under test baseline performance evaluation. The data quality and specific system parameters are such that the "scene" data collected can be merged or synthetically blended with the recent target signatures collected under a number of joint services target data base collection programs. By establishing a "comparable" data base of high quality scene data, the sensor/seeker community will have a high quality, highly flexible data base for concept development and evaluation. In addition to the 95 GHz data capability described in this paper, the complete multispectral data acquisition system, known as the Airborne Instrumentation System (AIS), will also provide coincidental infrared signature of the scene, providing data for multimode sensor/seeker development (i.e., 3-5 and 8-12 micron and 95 GHz). The radar is scheduled to be installed in a USAF C130 test bed aircraft in mid-1991. The AIS and C130 test bed together form the USAF Airborne Seeker Evaluation and Test System (ASETS) which is available for use by the RDT&E community. The following sections describe the design and special features of the 95 GHz radar portion of the AIS-ASETS.
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The LADAR (Laser Radar) is usually limited
in detection and tracking range under adverse
atmospheric conditions. The detection and
tracking are' degraded especially for ground
and low altitude systems. This work addresses
the optimized design of a dual mode
LADAR/RADAR system with respect to parameters
such as range and atmospheric conditions.
Computational results for specific RADAR
Systems show improvement for ranges beyond 30
km.
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The self-mixing heterodyne concept has been used in a highly coherent 140GHz radar, which places minimal stability requirements on the source signal itself. Two-dimensional images of simple rotating targets were generated with the CW system through focussed synthetic aperture processing.
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This paper reveals potential applications of high-temperature superconductors in microwave and millimeter-wave circuits. Implementation of superconductivity technology will significantly improve the performance of microstrip lines, chirp filters, delay lines, amplifiers, oscillators, and switching networks. Superconductivity offers compact packaging, ultra-high switching speeds, minumum loss, lowest power dissipation, and minumum signal distortion.
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GTRI has been involved in the design, development, and testing of a high-power, coherent, 95 GHz radar for use in developing and evaluating signal processing techniques for target detection, discrimination, recognition, and tracking. The system — designated HIPCOR-95 — operates in several data collection modes including polarimetric and extremely wide bandwidth (2,000 MHz). The system design is described with emphasis on recent testing to evaluate the high range resolution capability. Range resolution of 4 inches has been demonstrated.
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Experimental results obtained from a propagation study at 55GHz in a busy traffic environment are presented. Results show that frequencies in this region are a viable proposition for use in a microcellular mobile radio system.
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The performance of various PET oscillators with reaction, transmission, reflection, or feedback stabilizing cavity is compared with respect to loaded quality factor, output power, and AM and PM output noise. The oscillators are operating in fundamental or harmonic mode.
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The use of various harmonic orders permits an unprecedented frequency coverage, from X band to submillimeter, in a single apparatus, with an excellent dynamic range. The characterization of components, antennas and dielectrics, as well as solid state physics studies, are among the many possible applications.
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This project was the design and development of a state- of-the-art 60 GHz downconverter that demonstrates 5.0 dB noise figure and 55 dB gain across a 1.0 GHz bandwidth. To this performance we utilized High Electron Mobility Transistor (HEMT) device technology and advanced millimeter wave hybrid microwave integrated circuit capabilities.
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An NPL far infrared cube interferometer has been modified to bring the beam to a focus in each arm for measurements on small samples (≥ 3mm diameter) by reflection dispersive Fourier transform spectroscopy (DFTS). The performance of the instrument will be demonstrated with measurements on a selection of specimens, including compound semiconductors.
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A new dispersive Fourier transform spectrometer is designed to measure some ferrimagnetic properties such as the resonance line position, the real and imaginary parts of complex magnetic permeability and real and imaginary parts of complex dielectric permittivity as a continuous function of frequency, for the first time in the microwave frequency range as well as up to one millimeter wave frequency range. Our experimental results show that this spectrometer system has enough energy throughput and sensitivity to measure some very lossy and comparatively thicker ferrimagnetic materials.
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A measurement system is presented which analyzes between 143 GHz and 146 GHz three consecutive TEMooq modes of a hemispherical Fabry-Perot resonator mounted into a gas flow cryostat. The major factors that determine the accuracy of the observed dielectric parameters are discussed. It is found that low dielectric loss can be measured at a level of tan δ = 10-5 which is exemplified for AI2O3 studied between 90 K and 330 K.
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An automated open resonator system is designed and constructed for precision measurement of loss tangent and dielectric permittivity of low absorbing materials at 60 GHz. The use of high Q hemispherical Fabry-Perot cavity together with highly stabilized synthesized phase locked Gunn oscillator sources and the super heterodyne receiver enabled us to measure loss tangent value as low as 10 micro-radians. Both Cavity length variation and frequency variation techniques were utilized to provide precision data.
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For a variety of electromagnetic shielding applications mass-produced absorbing foil is available of which only D.C. surface resistance data are blown. Using a simple quasioptical arrangement die data at mm-wave frequencies are derived from reflection minima and the approximately known dielectric properties of the basis material. The range of validity of the measurement is discussed. Data for carbon- filled polycarbonate and indium-tin-oxide-coated PET foil are given.
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Synchrotron infrared radiation is about 1000 times brighter than blackbody radiation of T=2000 K. At Brookhaven National Laboratory,it is more powerful in the long wavelength region even if the largest area times solid angle which can be used by a He cooled bolometer is considered.
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We develop a new first-principle approach for the calculation of effective complex indices of composites bssed on the the iterative solution of Dyson equation of electromagnectic wave scattering in inhomogeneous media.
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A millimetre wave, quasi-optical reflectometer has been constructed. The instrument operates as a nulling complex reflection bridge, in which nulling is implemented at the signal frequency by polarising interferometery. In principle, the optical bandwidth of the instrument is about 70-500 GHz. Reflectivity standard errors of 0.05% in amplitude and 0.1° in phase have been demonstrated in w-band.
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A perturbation technique is presented to analytically model various electrical characteristics of ion-implanted MESFETs. It involves on the determination of the potential distribution in the irregularly—bounded depletion region under the gate by solving the two-dimensional Poisson's equation.
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We report design and performance of an ellipsoid optical system with a heating pipe cavity and a gold-coated horn for measuring IR emission of low absorptance samples at 50-150° C. The system includes also a set of IR interference filters and a spectral data processing system.
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This paper reports about numerical optimization calculations on mode converters to generate high-order TEm,n modes (TE22.2 at 110 GHz, TE12,2 at 120 GHz, TE15,2 and TE10,4 at 140 GHz) in oversized circular waveguides for conversion efficiency optimization studies (cold-tests) on high-power quasi-optical gyrotron output mode transducing antennas in the millimeter wave range. Multistep TE0.1 - to - TE0.n - to - TEm,n conversion sequences using periodic radius and m-fold (corksrew-type) wall perturbations provide theoretical output mode purities around 99 % . Measured values are (97 ± 3) %.
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The design of quasi-optical antennas for Whispering Gallery Mode gyrotrons requires an exact knowledge of the amount of power in the co- and counter-rotating mode. For the experimental verification of the theory a device consisting of a piece of waveguide with holes along the azimuth and a receiving antenna has been designed and investigated. From the radiation pattern of this leaky wave antenna the amount of power in the co- and counter-rotating mode can be evaluated.
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A mode converter for whispering gallery mode gyrotrons has been designed and tested. Experiments were performed on a megawatt power level, 3μs pulsed gyrotron operating in the TE16,2,1 whispering gallery mode at 148 GHz. The converter consists of a helically cut waveguide launcher and a doubly curved reflector designed to focus the radiation into a Gaussian beam. The launcher and reflector were designed using geometric optics. The experiments show that the converter focuses 80±7% of the incident radiation in the TE16,2,1 mode in a focal spot.
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A coaxial analogue of the Vlasov converter is described which transforms a whispering gallery mode into an oversize rectangular TE01 mode, which can in turn be transformed into the HE11 mode by standard techniques.
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Improved equivalence principle and physical optics based models for predicting the radiation from TE0n and TM0n mode Vlasov launchers are discussed. Theoretical far-field and numerical near-field radiation patterns are compared to measured results. Modifications to the unperturbed waveguide currents are explored and the resulting radiation patterns compared to measured results.
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In conventional microwave tubes electron beams propagate through structures which effectively reduce the phase velocity of electromagnetic waves below the speed of light in vacuo. In such cases, an electron beam propagating parallel to the waves with a velocity close to the wave phase velocity can engage in a resonant interaction with a high intrinsic efficiency.
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Relativistic backward wave oscillators (BWOs) have proven to be efficient, high power microwave sources in the centimeter and millimeter wave range, capable of radiating hundreds of megawatts of power. One approach to increasing the power generating capabilities of these devices is to introduce plasma into the device.
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A nonlinear time-domain analysis of the orotron is presented. The e.m. field in the
cavity is expanded into the Hermite-Gaussian modes with time-dependent amplitudes,
for which a set of ordinary differential equations is obtained from Maxwell's
equations. The equations for the amplitudes are coupled to the equations of motion for
the electrons. The calculations yield transient and steady state behaviour, saturated
efficiency and output power of the device.
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An experimental research program is being established at the University of Wisconsin to study free electron Cerenkov Masers as sources of coherent millimeter waves (30-300 GHz).
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The Naval Research Laboratory (NRL) is exploring the feasibility of deploying high temperature superconductivity (HTS) devices and components in space. A variety of devices, primarily passive microwave and millimeter wave component, have been procured and well integrated with a cryogenic refrigerator system and data acquisition system to form the space package, which will be launched late in 1992. This Space Experiment will demonstrate that this technology is sufficiently robust to survive the space environment and has the potential to significantly improve space communications systems. The devices for the initial launch (HTSSE?I) have been received by NRL and evaluated electrically, thermally and mechanically and will be integrated into the final space package early in 1991. The performance of the devices will be summarized and some potential applications of HTS technology in space system will be outlined.
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We analyze dielectric liner and periodic planar guides for moderate power, low voltage sources of millimeter waves. The analysis shows that optimum gain utilizing thin, high dielectric constant liners can be obtained at lower voltages (< 75 keV). A companion analysis of periodic gratings shows that large depth gratings (0.75<p/d<5.0) allows a comparable millimeter range spatial wave growth (2-5 dB/cm) at moderate beam voltages. We present results of analysis for the Streaming Beam Experiment (SBX) which is under construction at the University of Wisconsin.
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The recently developed concept of scalarized photons (as photons of any polarization) is proving to be rather helpful when dealing with spontaneous emission with an arbitrary number of harmonics. Specifically, the spontaneous emission due to spiraling electrons in a uniform magnetic field will contain at least forty harmonics that are emitting significant amounts of energy. The harmonic polarizations are automatically summed up through the concept of scalarized photons, and all that is left to be done is to sum up numerically integral harmonic energies to yield the numerical value for the energy of the spontaneous emission. Presently this program is being carried out for electron energies from one to sixty MeV.
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By making use of the parametric-amplifier model,this paper analyses the effect of the space-charge waves in Raman free electron laser with an axial guide field, it is shown that without taking the initial transverse velocity into account, kW vZO <wC is a necessary condition under which the scattered wave couples the slow space-charge wave. The dispersion relation and gain of the scattered wave,as well as the matching condition between the scattered wave and the space-charge wave, are derived.
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The results of an intercomparison between a photoacoustic determination of power propagating in free space and the UK National Standard of microwave power in waveguide at 94 GHz will be presented.
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We describe developments to improve reliability and power handling for high frequency applications in whisker contacted Schottky barrier diode mixers, detectors and multipliers fabricated by using sputtered refractory metals and silicides. The lift-off process has been used to fabricate diodes on GaAs with ideality factors of 1.18 and 1.06 for W/GaAs and TiSix/GaAs contacts respectively.
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Heterodyne receivers employing SIS tunnel junctions as the nonlinear mixing element have been developed in recent years for frequencies up to a few hundred GHz.
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This paper discusses mixers based on the nonlinearity of the two-dimensional electron gas in a device which is similar to a HFET, but without the gate. The low parasitic reactance of such elements make them potentially very useful in the millimeter-wave and submillimeter wave range.
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A technique has been developed for making 5-parameter measurements of whisker contacted quantum-well diodes with an HP 8510B automatic network analyzer. Special mounts with K connectors were designed to enable measurements up to 20 GHz. Several different quantum-well diodes were succesfully measured. The voltage dependent conductance and capacitance were calculated from the reflection coefficient of each device. These are the first reported 5-parameter measurements in the negative differential resistance (NDR) region of quantum-well devices.
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This paper demonstrates the capability of resonant tunneling diodes as microwave and millimeter-wave video detectors. In Ka Band an open circuit voltage sensitivity of 1750 mV/mW is measured. The detector properties are found to be a strong function of diode bias and the measmed tangential signal sensitivity and dynamic range are found to be smaller than existing devices.
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Beats between the harmonics of a microwave signal and various submillimetre laser lines above 890 GHz have been observed in the output from NbN Josephson junctions. Results of these mixing experiments will be described and discussed.
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A broadband second harmonic mixer was developed using unigue planar transmission line design techniques. Prototype devices demonstrate broadband performance from 18 GHz to 40 GHz with local oscillator (LO) drive levels of +13 dBm. A novel internal circuit topology allows for a full band coaxial interface (precision 2.4 mm or K connector) or band limited waveguide interface increasing overall configuration and integration flexibility. The design approach can be modified for fundamental or even harmonic (2) mixing schemes depending on available LO source.
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Evidence is mounting that the normal state properties of high-Tc superconductors (HTS) may be accounted for using a quasi-two dimensional Fermi liquid model with low carrier concentration. We present preliminary results of magneto-transport measurements on thin films of YBa2Cu3O7-y and GdBa2Cu3O7-y which support this model. Initial results from cyclotron resonance experiments suggest an effective mass in YBa2Cu3O7-y which is 1.4 times the free electron mass.
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Two new uniplanar mixer designs are described. These mixers are being tested at ifA-band, but will be scaled to higher millimeter wave frequencies. The goal is to develop broad-band monolithically integrated mixers which utilize surface-oriented hot electron devices as nonlinear elements.
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The mixer mount for a 75 -110 GHz SIS (superconductor-insulator-superconductor) receiver was scale modeled at 2 - 8 GHz . The mixer mount had a 4-step Chebychev single ridge transformer to launch the rf signal from the waveguide to a microstripline circuit. The microstripline circuit coupled the rf signal into the on-chip SIS element. A wire inductor in parallel with the mixer was used to tune out the capacitance of the SIS junction. Both the junction and the inductor had rf grounds provided by 90° radial stubs. In the scale model, a 50 Ω chip resistor in parallel with a 1 pF chip capacitor was used in place of the SIS junction to measure the rf matching properties. The inductor was modeled with a thin copper wire. The VSWR of the entire mount was less than 2.1 : 1 over the frequency band corresponding to 75 - 107 GHz. Receiver measurements with the actual mixer mount employing trilayer SIS tunnel junctions gave similar trends across the band.
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Since the discovery of high Tc superconducting (HTS) materials, considerable experimental and theoretical work has been done on possible applications to microwave and millimeter wave devices.
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We have constracted a Mach-Zehnder type interferometric spectrometer in the millimeter wave region (75 - 170 GHz) to measure optical constants of solids. Using this spectrometer, we have measured complex refractive indices of silicon crystals with various resistivities (1 - 300 Ω -cm). The density and relaxation time of carriers are determined by the experimental dispersion of the refractive indices using the Drude model. The refractive indices in this region are compared with those measured by the far infrared Fourier spectrometer.
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The dielectric properties of silicon with d.c. resistivity of 1.6-1.7.104Ωcm and 1.5-1.9.103Ωcm have been determined at 300 K for the frequencies of 34 GHz and 145 GHz, and between 70 K and 200 K for 145 GHz. The dielectric loss levels at 300 K are directly related to the resistivity data, while at low temperatures, the dielectric properties indicate that more complex interaction processes are involved which in particular give rise to a maximum in dielectric loss around 150 K for the lower resistivity grade.
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Polycrystalline Ge film has been deposited on glass substrate by vacuum
evaporation and plasma assisted deposition in hydrogen plasma. Electrical property
and X-ray diffraction spectra of the film deposited at various substrate
temperatures were measured. It was found that the plasma-assisted deposition method
in hydrogen plasma can give the possibility of lowering the growth temperature
during Ge film deposition comparing to the vacuum evaporation.
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Experimental investigations of the substrate deposition temperature and annealing temperature influence on aluminum films deposited on diamond substrates were conducted. Tests were performed at direct current and at 101.55 GHz. Minimum resistivity levels, near theoretical predictions, occurred for deposition temperatures in the range of 50-160°C and for peak annealing temperatures of 100-120°C. Both colder and hotter substrate temperatures resulted in larger resistivity levels.
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Results are presented of time dependent measurements of the spatial temperature distribution in a fused silica window mounted in a waveguide excited with 60 GHz gyrotron radiation in the HE11 mode. Power levels greater than 150 kW were used with pulse lengths exceeding 2 seconds.
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Fourier transform spectroscopic transmissivity data in the far-infrared (10 - 350 cm-1) were used to derive a model for the complex refractive index (n - ik) of polycrystalline diamond films grown by microwave plasma enhanced chemical vapor deposition. Due to their polycrystalline nature, the diamond films exhibited a surface roughness with crystallite sizes ranging from 0.1 - 8 μm. Scattering of the far-infrared radiation introduced by the diamond's rough surface is shown to have a significant effect on the FTIR spectrum and is accounted for in the determination of the material's optical properties. Free carrier type absorption (k proportional to λ2) is observed at longer wavelengths (l/λ < 100 cm-1).
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We found new effect which changes g-values of pair and trimer Co2+ spins by EPR of Rb2CO0.3Mg0.7 at 220, 370, 762.2 and 693.6 GHz in pulsed high magnetic fields. The anomalous g-values come from mixing of λLS and strong exchange interaction.
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We report measurements of the temperature, frequency, and rf field dependence of a wide variety of high-Tc superconductors in bulk, film, and single crystal form. The potential of current materials and fabrication processes for large-scale, high frequency and high power applications are evaluated.
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The technique of tailoring the complex refractive index of an artificial dielectric material has been developed at the University of Lowell Research Foundation (ULRF). Low reflection coatings, generally referred to as Dallenbach layers, have been designed for metal substrates using the artificial dielectric. The method of characterizing materials for the purpose of tailoring their dielectric properties at terahertz frequencies will be discussed. Results will be shown for a typical dielectric coated aluminum plate specifically designed for low reflection behavior at ? 0.6 terahertz.
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The melting and crystallization characteristics of three compositions in the albite-anorthite system were studied in a conventional thermal field and a microwave field by using a polarized light optical microscope test with refractive index oil immersion mounting, and x-ray diffraction.
Three mixtures of albite (Ab) and anorthite (An) were melted and then held at a constant temperature (1200°C) for varying lengths of time in a 2.45 GHz electromagnetic field. The same mixtures of albite and anorthite were held at 1200°C for 64 hours and 128 hours in a conventional furnace. All heated charges were air quenched after a desired duration time at 1200°C.
All three conventionally heated compositions of albite and anorthite showed the presence of crystalline phase. Only a trace of crystalline phase was found in 90 wt% Ab-10 wt% An at 1200°C for 64 hours in a conventional furnace. The amount of crystalline phase was found to increase as the anorthite content was increased. The mixture of 72 wt% Ab-28wt% An held at 1200°C for 128 hours in a conventional furnace had the largest amount of crystalline phase.
For the samples heated in a 2.45 GHz electromagnetic field, all compositions heated for 1 hour to 64 hours and the 90 wt% Ab-10 wt% An heated for 128 hours showed no trace of crystalline phase. The compositions of 81 wt% Ab-19 wt% An and 72 wt% Ab-28 wt% An showed some crystalline phase, but the amount of crystalline phase was much less than the samples processed in a conventional furnace.
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A Bragg reflector composed of periodic cylindrically symmetric corrugations can provide a reflection of nearly unity through the principles of constructive interference, resulting in a frequency selective resonator for overmoded high power oscillators as Gyro-TWT,CARM or FEL. Improved Bragg reflectors with Hamming- or Kaiser window distribution of the slot depth have been optimized using a scattering-matrix code. The features of such tapered corrugation amplitude are: high mode purity and ripple-free filter characteristics with predicable reflectivity. The field matching method (MAC) gives exact results even in the case when intercoupling resonances are close together and the simple coupled-mode theory is not valid.
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A reflector-antenna synthesis procedure based on the principles of geometrical optics (GO) will be applied to the design of a quasi-optical converter which is used to transform the output of the whispering-gallery-mode (WGM) gyrotron to a freespace beam. The amplitude and phase distributions across both transverse dimensions of the free-space beam are specified as design parameters. The exact reflector surfaces which yield the desired output-beam characteristics are determined self consistently as the solutions of a system of first-order partial differential equations which we solve by progressive integration across the face of the reflectors. The synthesis procedure is anticipated to improve the output-beam characteristics of previous Vlasov-type converter designs where the power distribution could be manipulated in only one dimension across the beam which results in relatively poor free-space propagation charasteristics and reduced coupling efficiency into guided wave systems.
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Excess heating of the high power gyrotron resonator due to ohmic losses may cause irreversible changes of the resonator geometry. Thus the oscillating frequency is shifted and multimoding may be difficult to be prevented. The following questions have been examined in order to support the construction of a TE03 gyrotron resonator at 140 GHz: Do harder copper alloys have any advantages? How do wall losses depend on the manufacturing process? The paper presents the measured surface resistances of oxigene free copper and different copper alloys. These materials have been machined with different processes. The surface resistance is determined by measuring the Q-factor of a cylindrical cavity at 143 GHz.
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A series of electron cyclotron masers (ECMs) have been successfully designed and operated over the past 10 years at Strathclyde University culminating in the highly tunable 35 to 200 GHz Mk 6 maser. High power masers require for certain applications a plane polarized pencil beam. In order to utilize the broad-band tunability of the maser, it is necessary to use a mode conversion process which is independent of frequency. The single mode serpentine and ripple-wall waveguide converters are therefore not applicable in this case. A quasi-optical mode converter of the Vlasov (step-cut radiator) type was constructed and used to successfully convert different TEmn cylindrical ouput modes of the maser into a highly directional pencil beam at several operating frequencies.
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Bi-directional couplers for very overmoded tubular HE11 waveguides (consisting of arrays of coupling holes in mitre bends) as well as for Gaussian beam waveguides (consisting of phase gratings with small amplitude on mirror surfaces) have been designed, fabricated and tested at 70 and 140 GHz. High directivity and good mode selectivity have been obtained.
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This paper discusses the solution of the cylindrical waveguide with sinusoidally perturbed walls for gyrotron applications using the boundary residual method.
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A Bragg reflector composed of periodic cylindrically symmetric corrugations can provide a reflection of nearly unity through the principles of constructive interference, allowing the creation of a frequency selective resonator. Measurements of reflectivity for both rectangular and sinusoidal corrugations are presented.
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Varian is carrying out the development of high-power, CW gyrotrons at frequencies ranging from 100-140 GHz. Initial test vehicles at 140 GHz have been designed to generate short-pulse power levels of 1 MW and up to 400 kW CW. Thus far, short-pulse power levels of 1040 kW have been measured at 38 % efficiency and average powers of 200 kW have been achieved. Output power levels of 400 kW have been obtained for pulse durations of 0.5 sec.
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A high power gyrotron with a built-in a-cut Vlasov-type mode converter was experimentally studied. The cavity was designed to operate in the TE12,2 mode at 120 GHz. A converted wave of a linearly polarized mode was focused near the output port by using reflectors. The output wave obtained in the test had a circular power profile of 28 mm diameter (FWHM) and had a maximum power of 548 kW with an efficiency of 30.4 Z.
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Penetration Depth and surface resistance are very important parameters not only to high Tc superconductor itself but also for design of circuitry and devices made by using high Tc superconductor.
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The GT92-5P/2 is a Quasi-Optical Gyrotron which shall proof that such a device is a useful and well developed tool for fusion plasma heating. Two resonators inside the vacuum vessel make it possible to operate it at 92 GHz as well as at 185 GHz. The power expected at fundamental is 500 kW, at a pulse length of 10 ms. Many new features, such as diffraction coupling mirrors and attenuated meshed beam ducts are introduced to guarantee reliable operation.
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The efficiency and output power of our 140 GHz MW gyrotron are greatly improved using a two-section cavity. In both TE15,2 and TE16,2 modes the gyrotron can produce more than 1 MW power at the efficiency of about 30%. The maximum power of 1.2 MW at 32% efficiency is produced at 148 GHz with TE16,2 mode. All these experimental results are quite reproducible. New designs of high efficiency cavities are ongoing, including the design of coaxial cavities.
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The design of a 1 MW, 280 GHz gyrotron suitable for ECR heating is complete and under construction at MIT. A highly overmoded cylindrical cavity with linear tapers at each end will operate in the whispering gallery mode; TE42,7,1. The magnetron injection gun (MIG) was optimized to produce a 90 kV, 50 A annular electron beam with an α = υ/υ|| =1.6 and a perpendicular velocity spread of approximately 5 %. The MIG and a 12 Tesla superconducting magnet with a 5 inch warm bore are presently under construction. Initial operation is planned for early next year.
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A simple, single-stage collector has been tested on the quasioptical gyrotron (QOG) experiment at the Naval Research Laboratory (NRL). This is the first application of a depressed collector to a high-power gyrotron, and was relatively easily accomplished due to the natural separation of the electron beam and the output power in the QOG. Collector efficiencies as high as 50% and overall efficiencies up to 16.1% were observed. The output power reached 431 kW with an overall efficiency of 12.7% and a collector efficiency of 40.7%. The collector efficiency was limited in this experiment due to interception of a portion of the electron beam on an undepressed section of the beam guide.
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Design of a depressed collector system for a quasi-optical gyrotron, which had a severe constraint on the maximum allowable radius of the collector region is outlined. The needs for unwinding of spent beam and for energy sorting could be accommodated by precise control of the magnetic field profile, especially in the collector region. Techniques used for defining and obtaining such profiles; and for dovetailing the profile with the collector geometry are discussed. Results on profiles and electron trajectories are presented, which demonstrate the feasibility of the design. From primary electron trajectories a collector efficiency of up to 68% has been calculated for a three collector design.
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This work presents a software for analysis and synthesis of four types of planar lines used on the millimetric wave band: Suspended Microstrip Line, Inverted Microstrip Line, Suspended Stripline and Broadside Coupled Stripline. Conceived for IBM/PC or compatible microcomputers,the program can study each configuration at a time or all of them at once.
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In this paper, the unilateral finline characteristics including finite metallization thickness and depth of mounting grooves are analysed by transverse resonance principle combining moment method. The numerical results are obtained. Finally, a set of explicit formulas for the propagation characteristics of unilateral finline are developed. To be conpared with the rigorous numerical results, the errors are ±1 % for phase contant and ±2% for characteristic impedance.
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The waveguide model with magnetic side walls was used for the analysis of a microstripline on the spherical surface of a dielectric substrate along one of the sphere's parallel circle. Expressions for obtaining the cutoff frequency, fc, the guided wavelength, λg, and the characteristic impedance, Z0, were developed for the (m, λ) mode of propagation and are of interest for the design of these lines.
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Heterodyne receivers are used in a variety of applications including communications and radar as well as atmospheric, planetary, and astrophysical remote sensing programs. A proper rf embedding circuit is required to optimize the performance of the nonlinear mixer in these receivers. In particular, low noise and high conversion efficiency have made superconductor-insulator-superconductor (SIS) tunnel junctions well suited for millimeter wave and submillimeter wave mixer applications.
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This paper presents a modified configuration of the NRD leaky wave antenna. A tunable aperture is introduced at the radiating open end. The taper in the antenna amplitude distribution is easily achieved by changing the height of the aperture instead of positioning the dielectric slab, which results in the easy design of such an antenna and the reduction of the requirement for the flexibility of the dielectric slab. The numerical results show that when the height of the aperture is appropriately chosen the phase constant is almost independent of the distance between the right-hand dielectric-to-air interface and the open end.
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The potential for submillimeter-wave laser relative reflectivity measurements with an accuracy of better than 10-4 (corresponding to a potential for relative measurements of surface resistivity with an accuracy better than 10-2 Ohms per square) has been investigated. An experimental arrangement to minimize the effects of changes in laser output and detector drift to levels, necessary to obtain this accuracy has been demonstrated. This was accomplished by simultaneous measurement with a reference detector to reduce short-term fluctuations and rapid sampling to account for longer term drift. Systematic error due to reproducibility of alignment with sample changes limited the present preliminary results to an overall accuracy of approximately 10-2 This achieved level of accuracy is sufficient for measurements of present state-of-the-art thin film high Tc superconductors at 77 K, an example of which is presented here.
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We present here a systematic analysis of some extra-ordinary dispersion characteristics of dielectric grating waveguides. Such characteristics are due to strong couplings of modes in gratings of high refractive index, including intra and inter-polarization couplings. Numerical results are given to illustrate and to explain the extra-ordinary couplings under various operating conditions.
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Radiation losses due to the curvature in rectangular dielectric waveguides with a step index of refraction profile in its upper and lower faces are examined here. Expressions are obtained for the propagation constants along the x and y directions of the waveguide, for the conversion coefficient, c, and for the attenuation coefficient, a. Appreciable radiation loss reduction, when compared with the homogeneous waveguide, is observed.
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In this paper, the eigenvalue problem of radially inhomogeneous circular dielectric waveguides is solved by the microwave multimode network method. The EM field boundary value problem is represented by equivalent coupled radial transmission line networks, which give clear physical pictures of the coupling characteristics of the EM fields; and the whole calculation procedure is significantly simplified. Numerical examples show that the present method is simple, accurate and versatile.
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A numerical solution for nonlinear TE guided waves in multilayer dielectric structures is presented. No restriction is imposed on the number of layers, on the type of the nonlinearity non on the distribution of linear refractive index distribution. This solution allows the investigation of the occurrence of hysteresis, instability of the waves and routes to chaos.
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Recently the application of the equivalence principle to the analysis of dielectric- loaded cavities was suggested. In comparison to other methods this method transforms the problem of .solving a three-dimensional discontinuity into a two-dimensional problem over the surface of the inserted body, which drastically reduces the size of the involved characteristic matrix. Now this method has been extended to the analysis of dielectric-loaded cavities which are coupled to waveguides. In particular, if the cavity is a waveguide section which is coupled at both sides to similiar waveguides, the method can then describe scattering inside infinitely long waveguides.
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Magnetic fields are the most adequate tools for tuning electronic energy levels in a controlled way. In contrast to homogeneous electric fields the resulting energy levels are stationary.
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A physical model is presented for the non - destructive determination of free carrier density profiles. The accuracy of the method with respect to quantitatively determine the profile function is enhanced by using the asymmetrical IR - reflectivity and the IR - transmission as well as 6 different measurable differential magnetooptical interference effects caused by the same free carrier profile. The results are compared with other methods used to determine profile functions such as SIMS, spreading resistance, Rutherford backscattering and stripping Hall measurements.
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The number (n) and mobility (μ) of the photo-created conduction electrons for several shallow donor transitions in high mobility n-GaAs have been studied as a function of FIR power and temperature. Both n and μ depend on the FIR power. The obvious consequences for the usual analysis of time-resolved and saturation experiments of FIR induced conductivity σ, where always a constant value for μ is assumed, will be discussed.
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The free carrier recombination in high-purity p-Ge was investigated by FIR saturation spectroscopy of photoionization. The results were analyzed in terms of a kinetic model yielding the saturation intensity and the recombination time.
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Microscopic electron sources are of current interest due to their potential of initiating a high energy electron beam at high repetition rates and short pulse widths. This paper describes a possible new microscopic electron source, via model, based on the microchannel plate concept. The model predicts current densities on the order of 1 A/cm2. Further, with an appropriate bulk electron injection scheme, current densities of greater than 10 A/cm2 are predicted.
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The microwave cyclotron resonance followed by the far-infrared laser cyclotron
resonance has become powerful aid to our understanding of the intrinsic characters
of typical semiconductors.
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A low noise superheterodyne receiver has been designed and constructed for the ground-based monitoring of stratospheric ozone. The receiver measures the ozone spectral line at 110.836 GHz. The low-noise front-end consists of a Schottky-mixer, a HEMT-amplifier at 3.6 GHz and a phase-locked Gunn-oscillator as LO and is followed by an acousto-optical dual spectrometer with 1.2 GHz bandwidth and 85 kHz resolution at the band center. A tunable passive cold load is used as a reference load.
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In a magneto-optical study of TEA(TCNQ)2 with an optically pumped FIR laser and correspondingly high magnetic fields, EPR signals with g=2 were observed. A detailed study, including comparison with results at microwave frequencies (X- and K-band) will be presented.
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FIR-magneto-spectroscopy is one of the most powerful tools for the experimental investigation of the quantum structure of semiconductors. In fact, the only straight-forward approaches for a direct determination of single-electron band parameters are the standard magneto-transmission and reflection experiments.
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FIR optically pumped laser lines provide a convenient comb of frequency stable local oscillator for heterodyne detection f Unfortunately the relative efficiency of the available laser lines is difficult to estimate because many quite different experimental apparatus were used, and absolute reliable power measurements were seldom performed.
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A new power meter with a sensitive micro-calorimeter has been developed to measure the absolute power of FIR laser. Using this power meter, a calibration of a Scientech power and energy meter of 36 series has been carried out for 337 μm wavelength.
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Schottky barrier diodes have a long and successful history of application in heterodyne receivers for millimeter and submillimeter wavelengths.
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The photodetection sensitivity of the Avalanche Breakdown (AB) photodetector at λ=151μm has been increased by shaping the detector element so as to trap incident radiation by total internal reflection. Pulsed laser signals have been detected at powers as low as 5 x 10-15 W, corresponding to the arrival at the detector of only 4-5 photons during each 300 ns laser pulse. Several mechanisms are considered.
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Microbolometers with a large negative temperature coefficient have been fabricated using an epitaxial GaAs layer grown at low temperature (LTGaAs). The detector elements used have potential in composite bolometer structures where high dR/dT materials can be used without having to be impedance matched to the antenna structure. The LTGaAs material exhibited a thermally activated conduction mechanism (Ea ~ 0.3 eV) with temperature coefficients of -0.05 K-1 and -0.02 K-1 at 110 K and 290 K respectively. Thermal impedance calculations suggest that the negative temperature coefficient produces filamentary electrical paths. Intrinsic dc detector responsivities as high as 108 V/W have been extracted from I-V measurements.
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A compact, high efficiency, 35 GHz, 200 KW, two cavity phase-locked second harmonic gyrotron is under development. It has several unique features: 1) a novel complex output cavity; 2) phase locking with subharmonic injection; and 3) low magnetic field requirements compatible with modern permanent magnet technology. A similar design could be applied to fourth harmonic operation at 94 GHz. The injection signal frequency for these two devices will be 17.5 GHz and 23.5 GHz respectively. This innovative gyrotron is expected to achieve performance capabilities unmatched by existing high power millimeter wave devices.
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This paper discusses the development of a monolithic GaAs anti-parallel pair of Schottky barrier diodes, and its integration into a G-band (183 GHz) subharmonically pumped mixer. The diodes’ IV characteristics are equivalent to those of the best whisker contacted diodes, and are well matched due to the design of the fabrication process. The performance of the prototype mixer is comparable to that of a similar mixer with whisker contacted diodes. This monolithic design is ideally suited for space applications at millimeter and submillimcter wavelengths.
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We manufacture thin-film Ni-NiO-Ni diodes for detection of 10 μm C02-laser radiation with the aid of electron and UV lithography as well as sputtering techniques. Minimum strip width is ≤ 0.35 μm, NiO thickness 50 Å and measured coupling factor ≥ 130.
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GaAs Schottky barrier diodes with subrnicron anode diameter and high epitaxial layer doping were used as mixer up to 2.5THz. First, mixer performance was investigated measuring system noise temperature versus local oscillator power at different frequencies. Second, two lasers were taken as local oscillator and signal, respectively. Signals at the difference frequency and at two higher harmonics were generated. The power of the mixing signal was measured as a function of bias current. The behaviour of the higher harmonics was unusual. The extreme case was a sharp dip of more than 20 dB and a 3 dB width of only 30 μA.
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Stratospheric trace gas observation is an important subject to understand chemistry and dynamics of ozone layer. The observation of the trace gases by millimeter and sub-millimeter wave radiometry is one of the most effective means to remotely sense upper atmosphere.
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Gyrotron development activities at the Centre de Recherches en Physique des plasmas in Lausanne are directed along two directions, quasi optical gyrotrons and, with less emphasis, cylindrical cavity gyrotrons. This paper will review the recent work performed in these two fields.
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The operating diagram of a low-Q (Qdiff=160) TE°01 gyrotron at 8GHz exhibits oscillations at, frequencies in a range around both 7 and 10GHz. These frequencies are identified as the backward wave (BW) and forward wave (FW) components of the traveling TE°21 mode. As the resonance condition of the BW depends on the average parallel velocity (<v||<) of the beam electrons (ωBW = Ωc/γ - k|| <v||<), the measurement of ωBW, for given Ωc and γ, yields the value of the velocity ratio (α=<v?</<v||<) and provides a diagnostic for ?. Experimentally, we have measured ωBW while varying Ibeam Ωc. and α. These results will be presented and compared to predictions of linear dispersion relation and of nonlinear simulations.
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Beam diagnostics which provide information for determining the velocity ratio α = β/β|| and the parallel velocity spread δβ||/β|| have been installed on the 140 GHz megawatt gyrotron. The velocity ratio has been measured to be a function of the beam current. Preliminary measurements of the velocity spread at low (≈ 5 A) beam current have been made.
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A diagnostic, based on Thomson scattering, for measurement of the velocity distribution in beams for gyrotrons is described. Using signal averaging to increase the signal to noise, good resolution of the distribution of velocities parallel to the tube axis is predicted. A typical measurement will take a few minutes.
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Influence of the magnetic field tapering on gyrotron operation is studied by generalizing the η(μ,F) plot, which is most useful for the optimization of a gyrotron design. It is found that in general a positive magnetic field taper increases efficiency, but at the same time increases the danger of self-excitation of parasitic modes, while a negative magnetic field taper decreases efficiency and reduces the probability of self-excitation of parasitic modes.
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In quasi-optical gyrotrons (QOG) using Fabry-Perot resonators designed to operate at the fundamental, the second harmonic interaction could be important due to the fact that the quality factor Q is an increasing function of the frequency. Emissions at frequencies twice the electron cyclotron frequency have been also observed experimentally in QOG as well as in cylindrical gyrotrons. In order to understand the nature of this unwanted emission and its effects on the efficiency of the quasi-optical gyrotrons, a simulation code, based on the slow time scale formalism is written to follow the time evolution of the fundamental as well as the higher harmonic modes. Results from the simulations of our 100 GHz QOG experiment will be presented.
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There is presently considerable interest in the development of high power microwave sources for accelerator applications and fusion heating.
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Analysis of the well-known dispersion relation for electromagnetic waves propagating in an uniform electron plasma with a magnetic field shows unexpected results near the cyclotron harmonics nΩ when the electron energies are relativistic. In particular, it can be shown that gain for waves propagating across the magnetic field will exist up to the harmonic number nmax = 0.1 A3γ6 , where A is the normalized transit-time 2ΩT for the interacting electrons and γ is the relativistic energy factor. For n < nmax , gain falls slowly with harmonic number, i.e. as n-1/3. Similar results can be inferred from relativistic quantum theory. Numerical solutions of the reduced dispersion relation substantiate the analytical approximations. The starting current for a quasi-optical synchrotron resonance maser oscillator is derived, and examples using a 2 megavolt electron beam are discussed.
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We calculate the conductor loss of a high Tc superconducting conductor backed coplanar waveguide. The inductance is calculated by the modified Spectral Domain Method(SDM). Then, the geometric factor is obtained by a numerical derivative of the inductance. This factor is used to calculate a conductor loss by the Phenomenological Equivalence Method(PEM).
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Certain high-power microwave tubes currently under development have their output in the TM01 mode in a circular waveguide. This mode has a transverse electric field in the waveguide which is completely radial and produces an open-end radiation pattern which is entirely in the θ (the polar angle) direction with a null on the waveguide axis. This radiation pattern is not optimum for most applications and it is often desirable to convert the TM01 mode into the TE11 mode which has its maximum on the waveguide axis, is approximately linearly polarized, and has a higher maximum directivity than the TM01 mode. In this paper, we discuss a TM01 - TE11 serpentine mode converter for a high-power backward wave oscillator operating at 8.6 GHz. Morgan’s method was used to derive the coupling coefficients and numerical computation to optimize the conversion efficiency. Test results are presented. Waveguide bends for TM01 and TE11 modes in an overmoded waveguide are also discussed.
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The spectra of forward an backward travelling parasitic modes generated by plane and curved, phase correcting mirrors in highly overmoded HE11 and TE01 corner bends (90°) have been measured using a wavenumber spectrometer (f = 70 GHz, I.D. = 27.79 mm, ka = 20.39). The experimental spectral distributions and the measured power levels in transmitted and reflected undesired spurious modes are in good agreement with theoretical predictions.
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Depolarizations due to melting layer and rain have been calculated for a polarized plane wave propagating through the layers of oblate spheroidal melting particles and raindrops in the frequency range of 1-100 GHz. These new results are useful in the design of earth-satellite communication links.
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Direct, high power TE01-HE11 mode converters in overmoded, circular corrugated waveguide (70 GHz, I.D. = 27.79 mm) with periodic curvature distortions in one plane have been optimized by numerically integrating the corresponding coupled-mode differential equations with new, generalized coupling coefficients. Since at appropriate corrugation depth the 'unwanted mode conversion to the surface modes TE11 -<EH11 and TE21+EH21 is negligible, it is possible to design short mode transducers with high conversion efficiency. Both, the input mode TE01 and the output mode HE11, have very low currents and electric fields at the waveguide wall (volume modes). Thus, the mode transformer shows very high power carrying capability by avoiding waveguide arcing at flange connections. The overall conversion efficiency was calculated to be 97.44% for a 3λΒ, and 98.40%for a 4λΒ mode converter, ohmic losses are included.
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The spectral domain approach is extended to analyzing the radiation of millimeter waves from a dielectric waveguide periodically loaded with thick metallic strips. The formulation views the electric current sheets on the upper and lower surfaces, and inside the strips as the source quantities to be determined so that the original problem is modelled as a multilevel-thin-strips-loaded dielectric waveguide, which, in turn, may be analyzed by the spectral domain approach. The radiation characteristics are demonstrated as a function of the strip thickness. It is shown that there is a significant difference in the leakage constants of TE and TM mode excitations.
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In this paper, the propagation characteristics of NRD waveguide loaded with periodic metallic strips are analyzed in terms of the method of lines. Numerical results show that such structures can be used as millimeter wave bandstop filters and NRD waveguide beam scanning leakage wave antennas.
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A new approach for analysis of dielectric periodic structures is proposed in this paper. The method combines the coupled-mode theory with Floquet theory and joins the eigenmode expansion with the space harmoinc expansion properly. As a result, the whole analysis procedure is significantly simplified. Numerical results for the filter characteristics of some dielectric periodic structures show that the present method is effective, accurate and useful.
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Propagation property of a circular dielectric waveguide with periodic metallic strips is analyzed by a rigorous formulation. The filter characteristics of the metallic strip loaded structure are carefully investigated for both TM and TE modes. On the basis of the analysis, some useful guidelines for the design of the filter are suggested.
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A spectral domain technique was developed for the analysis of scattering by conducting bodies inside cavity resonators which may bo connected to an arbitrary number of waveguides, The technique is applied to calculate the equivalent circuit parameters of conducting posts and strips in a rectangular waveguide. The theoretical results agree closely with the results.
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The occurance of the urinary stones varies according to the geographical regions. The presence of stones in the urinary system causes pain and discomfort. These generate colics and hence are sometimes life threatening. In the present study, infrared measurements have been made on several stone samples. It has been found that calcium oxalate, calcium phosphate, magnesium ammonium phosphate, calcium carbonate, uric acid,-cystine and xanthin are present, as expected. Also, silicon dioxide, is found to be present in some of the stones but in small quantity, in addition to the above constituents. This constituent is responsible to exhibit piezoelectricity in the urinary calculi.
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The behaviour of permittivity and loss tangent in the temperature range between 80 to 300 K of several alumina grades is presented. The data are obtained using a resonant cavity technique. The results show smaller temperature dependence for the polycristalline grades, in contrast with the observed behaviour of monocrystalline ones.
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The dielectric parameters of monocrystalline LiF and CaF2 were measured at wavenumbers between 1 cm-1 and 40 cm-1 by dispersive Fourier transform spectroscopy and Fabry-Pèrot resonators. The results are discussed in the framework of an one-phonon absorption model. Its shown that the parameters of the transverse optical phonon absorption band can be taken for an approximate assessment of the measured dielectric data.
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Photoacoustic spectroscopy ( PAS ) , which uses an optically pumped FIR waveguide laser as the radiation source, has been developed. The experimental results of Submm spectral absorption for some biological specimens are reported.
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The decay processes of the plasma layers generated by two intersecting microwave pulses in 1 torr dry air are investigated by Bragg scattering method. The results of measurement show that the electrons decay initially at the three-body attachment rate. However, when enough negative molecule ions are produced through the electron attachment process, the regeneration of electrons via detachment process is increased and eventually balances out the electron attachment loss. The net electron loss is then dominated by the recombination process.
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Two dimensional finite element analysis with absorbing boundary conditions is use to model a variety of window materials for Vlasov type high power microwave launchers. The results of this analysis are compared with experimental studies and optimal choices are identified.
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Schottky barrier varactor diodes are used as frequency multiplier elements for local oscillator (LO) sources for the millimeter and submillimeter wavelength region. These sources are used in heterodyne receivers for a variety of applications including radio astronomy, atmospheric studies and plasma diagnostics.
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We have demonstrated second harmonic generation (SHG) in polycrystalline ZnSe, GaAs and CdTe with OFID 10 μm CO2 laser pulses as short as 30 ps. We show and discuss SHG characteristics as well as autocorrelation functions of 30 ps 10 μm pulses measured with these materials.
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All-solid-state heterodyne receivers have been developed for millimeter wavelength applications. These receivers are compact, robust and power efficient; and are thus suitable for space-based applications.
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We have developed a new type of sharp cutoff high-pass filter and a new type of spectrometer. These devices have been tested and yield good agreement with theory. They are easier to use and more accurate than present devices.
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It has recently been shown that a microwave signal carried on a Schottky-contacted coplanar waveguide (CPW) on a GaAs substrate can undergo large phase shifts when the structure is optically illuminated, even at very low illumination intensities1. Past experiments have been made only for continuous (CW) illumination of the CPW. However, the response of the device to time-varying optical illumination is of great importance for microwave and optoelectronic applications where dynamic operation is required. In this paper we present preliminary measurements of response times of optically illuminated CPW phase shifters. Results indicate the possible presence of optically active semiconductor trap states with extremely slow response times, which dominate the microwave propagation characteristics of the CPW. A possible way to prevent this "optical back-gating" effect will also be discussed.
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Implementation of silica fiber devices based on stimulated Brillouin scattering(SBS) in near IR fiber optic communication systems is discussed for multi-channel SBS or SBS enhanced SRS amplification, switching and channel selection. Potential improvement in the mid infrered is anticipated.
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A new supervisory system using infrared and visible images has been developed. This system is used mainly for equipment maintenance and supervision. It has the following features: (1) Multimode supervision (2) High-speed detection of abnormalities at an early stage (3) Automatic supervision
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The experimental setup of a gyrotron which operates in the TE0,3 mode is described. The results of measurements with several gyrotron versions at short pulses (0.5 ms) and long pulses (100 ms) are reported. Designs for higher powers (up to 1 MW) using a nonsymmetric volume mode are presented. First experiments will use the TE10,4 mode. A quasioptical convertor for the output mode will be used, either in conjunction with an axial window or, later, with a radial window.
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Problems of unwanted mode conversion between the resonant cavity of GYROTRON IVA and experimental areas are minimized by (i) in the gyrotron, increasing the length of the transition from the cavity to the output waveguide, and (ii) outside the gyrotron, using a quasi-optical antenna at the output window to provide immediate conversion to a TE11 waveguide mode. Two applications, plasma scattering and measurements on dielectric materials are discussed.
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In a gyrotron the voltage depression1 due to the space charge of the electron beam creates in general potential traps for positive ions along the beam path.
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Electromagnetic Sciences, Inc., GTRI, and Millitech have teamed on a contract to NASA Langley Research Center to develop and deploy a space-borne, four-frequency, millimeter wave instrumentation sensor designed to characterize the plasma boundary layer on reentry. This paper describes the experiment, the system, and special features of the waveform and processing to solve the unique problems encountered in such an experiment.
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A stable operation of the KfK gyrotron in the TE03 mode was possible only with an eccentric hollow electron beam. In order to understand this effect, we study theoretically the influence of displacement of the electron beam from its central position in a resonator on efficiency and mode competition in gyrotrons.
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The quasioptical gyrotron at the Naval Research Laboratory will be converted to an 85 GHz gyroklystron by the addition of a prebunching resonator and an external source. The experiment will investigate longitudinal-mode selection, efficiency enhancement, and phaselocking in a quasioptical resonator. This paper presents results of the design calculations.
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We have developed a nonlinear, time dependent, multimode simulation code that allows us to study the operation of high power conventional cavity gyrotrons in the time domain.
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Stable single mode operation is a very important consideration in the design of high power microwave and millimeter wave sources.
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The negative energy cyclotron wave will couple to a positive energy, slow waveguide mode with a growth rate which can be even larger than the space charge mode for intense, high voltage electron beams. 2-D fluid theory, 1-D Vlasov theory and 1 2/2-dimensional simulations are presented along with the design parameters for a proposed proof-of-principle experiment.
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Although the application of millimeter wave technology offers a number of commonly known advantages /1/, wide spread application has long been hampered due to cost. Since the early 70's worldwide research and development efforts are ongoing. Today, the available component technology, e.g. planar technology for hybrid and monolithic integration or quasi-optic technologies /2/, has already fostered the spreading application of millimeter-wave systems in various, mostly commercial, employment areas. Ease of fabrication and the capability to integrate a wide range of circuit functions are of prime importance. The advantages and the disadvantages of different technologies are surveyed, compared and evaluated.
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Recent developments in solid-state devices and microwave integrated circuits have made it possible to integrate the active devices with planar antennas to form active antennas. This paper presents the recent technology advances at Texas A&M University in active antenna elements using patch, notch and circular ring antennas integrated with Gunn or FET devices.
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A Millimeter Wave Monolithic Amplifier has been developed. The two stage low noise amplifier design is based on noise/gain models developed for pseudomorhpic (InGaAs) HEMTs. The simulation of the design indicates greater than 12 dB of gain with a noise figure near 3 dB. The operating band covers the oxygen attenuation bands near 60 GHz.
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The grid oscillator is a planar structure that can combine a very large number of millimeterwave solid-state active devices. A 100-MESFET hybrid grid model is demonstrated at 5 GHz. The transistors in the grid self-lock with an effective radiated power (ERP) of 24 Watts and a conversion efficiency of 20%. An equivalent embedding circuit for a device in an infinite grid is found using symmetry. This equivalent circuit predicts the frequency of oscillation. Quasioptical injection-locking of the grid oscillator with an external signal has been demonstrated and analyzed.
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A four-bit monolithic phase shifter was developed for the 20.2 to 21.2 GHz frequency range. MMIC chip design, typical chip performance, and performance variations and yields are discussed.
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To prepare the future meteorological radiometric satellite missions, a millimeter-wave vertical sounder has been developed. Sounding both the 118 GHz O2 and the 183 GHz H2O lines, it provides simultaneously temperature and humidity profiles of the atmosphere. To validate the atmospheric parameters retrieving schemes at these frequencies, this radiometer is to be use for observations, successively from the ground, a plane and possibly a balloon.
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We have developed and tested a 21 element two-dimensional power-combining array, intended for transmitter applications in future deep space missions. The array uses MMIC phase shifters for beam scanning, MMIC power amplifiers and Vivaldi (Exponentially Tapered Slot Antenna) radiating elements. The measured combining efficiency, referred to the power amplifier output ports, is about 60%.
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In present quasi-optical (Q.O.) gyrotrons, the microwave power is coupled out by edge diffraction. Results of cold tests and hot tests show that the output is non-Gaussian. Recently, we have tested successfully output couplers using a grating reflector which replaces one of the resonator mirrors. This type of coupling produces almost perfect Gaussian output patterns so that one can utilize an additional perfectly reflecting mirror to focus efficiently the output microwave beam into a corrugated HE11 waveguide.
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A design of a MAGICTRAC (Microwave Antenna for Whispering-Gallery-Mode Conversion using a Twist Reflector Antenna Converter) device is presented for use on the MTX (Microwave Tokamak Experiment) transport system. The MAGICTRAC device, consisting of a mode converting waveguide taper and three metal reflectors, transforms the TE15,2 circular waveguide mode output of a VARIAN Associates 140 GHz gyrotron into a free-space Gaussian-like beam with < 95% efficiency. Dimensions of the MAGICTRAC are chosen to produce a beam matched to the MTX quasi-optical transport system.
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For future high-frequency (<100 GHz) high-power (≥ 0.5 MW) cw gyrotrons a cryogenically cooled window (CRW) seems to be a suitable vaccuum barrier pervious for the RF power.
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The absorption coefficient of most low absorbing materials increases almost linearly with increasing frequency. For ceramic boron nitride, this is opposite, the absorption decreases with increasing frequency atleast to about 600 GHz. Single crystal high resistivity silicon has the lowest absorption at room temperature in the entire millimeter wavelength region. Our new broadband continuous wave low temperature (76 K and 86 K) measurement on single crystal sapphire reveal that its absorption coefficient value is almost the same as its room temperature value around 90 GHz (0.05 Nepei/cm), then slowly increases to 0.07 Neper per cm at 290 GHz. The low tempertature absorption value then decreases to 0.015 Neper/cm at 450 GHz. Continuous broadband data on complex refractive index and complex dielectric permittivity at 4 kelvin will be available around the conference time. There is hardly any difference in its absorption value at 86 kelvin (compared to 76 kelvin). We do not see any advantage of using sapphire as a window material at 77 kelvin. Extra high resistivity silicon is by far the best window material as regards the absorption loss concerned.
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An apparatus has been developed for studying the conditions for avoiding arc breakdown in a low-pressure HE11 waveguide launching 60 GHz 200 kW radiation into a tokamak plasma and passing through a region of electron cyclotron resonance. The results of the first experiments are reported.
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The electron temperature is routinely measured on TORE SUPRA using Fabry-Perot cavities. These have been calibrated using a technique involving coherent addition and Fourier analysis of a chopped black-body source. Comparison with conventional techniques is reported.
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A four-level density matrix approach is used to show that the experimentally observed three-way correlation between J number, the local gain spectrum and the optimum operating pressure results primarily from pressure broadening effects.
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It may be possible to construct a new class of FIR gas lasers based on IR optical pumping of perturbation-allowed FIR transitions. They would be restricted to neither the low pressures required for OPFIR laser operation nor to the dearth of molecules with the chemical robustness required for discharge- pumped perturbation lasers. Salient features, including potential increases in laser efficiency, are presented and several candidate systems are discussed.
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The whole absorption spectrum of CH3OH between 30 and 1250 cm-1 has been measured on the prototype instrument of the Bruker Fourier transform spectrometer at the Physical Chemistry Institute of the University of Giessen.
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We have investigated the generation of superradiant far-infrared 496 μm CH3F pulses and produced for the first time 373 μm CH3CN superradiant pulses obtained by pumping with pulses from a hybrid 10 μm CO2 laser which are truncated by a plasma shutter of new design. Superradiance is confirmed by measurement of the pressure dependence on intensity, width and delay versus the pump pulse. We have observed pulse durations well under the limit of the inverse linewidth of the transition and obtained pulses as short as 3 ns in comparison to 14 ns previously reported by others.
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Atmospheric O2 has a host of absorption lines centered around 60 GHz. Spectral attenuation rates a in dB/km are calculated with the millimeter-wave propagation model MPM89.
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Methyl Alcohol is a very efficient molecule for generating FIR Laser lines because of the the complexity of its vibro-rotational spectrum. The presence of an internal degree of freedom, i.e. the rotation of the hydroxyl group around the symmetry axis of the methyl group, makes the selection rules less restrictive than for symmetric top molecules.
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We report new FIR laser lines from 13CH2F2 molecule optically pumped by a waveguide CO2 laser. The increased tunability (300 MHz) with respect to a conventional CO2 laser allowed to pump 13CH2F2 vibrational transitions of large offset. 34 new laser lines have been discovered, ranging from 113.1 fim to 491.4 pm in wavelength, thus increasing the number of the known FIR laser lines from this important molecule to 99. The frequency of six new laser lines was also directly measured by heterodyne detection with already known laser lines.
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In the frame of the conceptual design of the International Thermonuclear Experimental Reactor (ITER), the study of an advanced Electron Cyclotron Wave (ECW) system has been carried out.
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A tapered reflection-type gyrotron travelling-wave-tube amplifier (gyro-twt) operating in Ka-band is presently under investigation at NRL. The device incorporates precise axial tapering of both the magnetic field and the interaction circuit for broadband operation. The amplifier operates in the TE10 rectangular waveguide mode at the fundamental cyclotron frequency at a beam voltage of 33 kV and a beam current of 1.6 A. By employing an electron beam with an alpha of around 0.6, small signal gain in excess of 16 dB is observed over a wide instantaneous frequency range (33 %, 27-39 GHz), in good agreement with theory.
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A tunable gyrotron backward-wave oscillator has been constructed at MIT, and preliminary experiments demonstrated backward-wave operation from 133-142 GHz. A second phase of experiments will soon begin that will use a redesigned interaction region and beam tunnel, and a wide-band motheye window. Results from experiments and design improvements are discussed.
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A 94 GHz gyrotron designed to operate in the TE13 mode is under test. The expected output power is 150 kW for a beam voltage of 70 kV, a current of 10 A and a duty factor of 0.1%. Novel features, including a TE13-TE11 mode converter, will be discussed. Results of testing will be presented.
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Relativistic electron motion is considered in the axi-symmetric system, and a formalism which can be solved semi-analytically in any magnetic field profile is developed. As a special case, the analyses are applied to nonadiabatic magnetic compression of axis-rotating electron beams. The results, which have a direct application to the cusptron or the peniotron microwave tubes, are compared with the predictions obtained by assuming an adiabatic behavior of electron. Beam parameters such as off-centering, Larmor radius, and velocity are examined for optimum beam-wave interaction.
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A novel frequency multiplying device is analyzed which provides selective gain at the cyclotron harmonics in a quasi-optical gyrotron. The device utilizes a prebunching section which enforces a double-resonance condition on the generated radiation. This selects among cyclotron harmonics in the output cavity even though the cavity structure supports all harmonics. The prebunching is accomplished by modulation of electron magnetic moments by a low frequency input rf field. A design is given for quasi-optical operation at the third cyclotron harmonic (four times the input field frequency) with 10-15% efficiency and linear suppression of the lower cyclotron harmonics.
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A nonlinear self-consistent slow time scale simulation model has been developed to analyze the large signal behavior of a two-stage gyro-TWT. The results show that the performance of a two-stage gyro-TWT is more sensitive to velocity spread than a single stage gyro-TWT and the saturated bandwidth is narrower than that of a single-stage gyro-TWT.
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A Nd:YAG laser-induced, semiconductor switch for far infrared (FIR) radiation was mounted inside a free electron laser cavity to act as a intra-cavity output coupler. In addition to the demonstration of generating short, intense FIR pulses, the cavity dump coupler was used to perform steady-state saturation spectroscopy studies in the FIR.
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A nonlinear theory for the broadband operation of a slow-wave cyclotron amplifier with a dielectrically lined waveguide is developed to calculate the efficiency, gain and bandwidth. For a cold beam, the bandwidth ▵ω/ω = 6 % with η = 40 % but ▵ω/ω increases to 30 % if the amplifier is operated at η = 20 %. The sensitivity of η on the velocity spread will be shown.
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The effect of the voltage depression due to space charge on the beam parameters in a gyrotron is investigated. Although the voltage depression can be compensated to some extent by increasing the beam voltage, some loss of efficiency is to be expected, especially in the case of high currents and volume modes.
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For many applications a high-gain RF circuit is required. We present results of numerical analysis and bench-test measurements of our circuit with emphasis on parasitic mode suppression by lossy dielectric absorbers. Preliminary amplifier test results should be available at the conference.
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Microstrip antenna technology offers low-cost, efficient conformal antennas at millimeter wave frequencies. Microstrip conformal antennas eliminate weight, size, aerodynamic drag, reliability, and maintainability problems experienced by conventional antennas. Microstrip antenna technology is compatible with printed circuit and monolithic technologies. Microstrip antennas have distinct advantages in cost, pattern symmetry and reproducibility.
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In this paper, the diffraction field of quasi-optical resonator is first calculated by combining complex ray theory with GTD theory. The directional diagrams of diffraction field on E and H plane are given. Thus, the theoretical results predict that a quasi-optical power combiner may be used as an antenna to realize the unification of quasi-optical power combiner with the antenna.
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A moment method employing rooftop functions to represent both the volume polarization current in dielectrics and surface current on conductors is used to model patch antennas. Excellent agreement is shown between calculated and measured results for a microstrip patch antenna and reasonable agreement for a spiral antenna.
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Recent investigations have been conducted to extend the knowledge on phase-correcting Fresnel zone plate antennas for applications at microwave and millimeter wavelengths. Analyses and/or measurements will be summarized for parameters including efficiency, aberrations (related to scanning and multiple feed applications), bandwidth, far-field antenna patterns, surface reflections, and specialized applications. The recent results will be compared with those of earlier investigations.
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The radiation characteristics of the omni-directional periodic leaky wave antenna operating in TMoI mode is investigated by the improved perturbation method with a particular attention directed to the Brewster angle effect on the performance of the antenna, and some interesting results are given.
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The theoretical and experimental patterns and input impedance of a dipole-fed horn antenna in a ground-plane are presented. The results indicate that the E-plane patterns of a horn antenna in a ground-plane and a horn antenna in a two-dimensional array differ for angles greater than 40°. The input impedance and resonant length are a strong function of the dipole position inside the cavity, and vary from 40Ω to 170Ω and 0.37λ to 0.45λ, respectively. A dual-polarized horn antenna using a novel two- dipole feed is also presented. The orthogonal channels show identical patterns and -23dB polarization isolation at 92GHz. The dual-polarized antenna is well suited for millimeter- wave polarimetric synthetic-aperture radars, radio-astromomical receivers and highefficiency balanced-mixer receivers.
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A double-dipole antenna integrated on a thin dielectric membrane and backed by a large ground plane is presented. The double-dipole design results in nearly equal E and H-plane patterns with a gain of 12-13dB, cross-polarization levels lower than -27dB, and a main-beam efficiency of 90%. The input impedance is around 50Ω and will match well to a Schottky-diode or SIS detector. The measured coupling between two antennas with 1λ spacing is lower than 20dB. It is therefore possible to array the double-dipole antenna for diffraction-limited imaging. The double-dipole antenna is a simple antenna with a very low cross-polarization component useful for millimeter and submillimeter-wave applications requiring a ±5% bandwidth.
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In a free electron laser (FEL), the frequency scales as the square of the beam voltage divided by the wiggler period. Because of the favorable scaling with voltage, FELs show promise for operating at high frequencies.
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Two kinds of new broadside coplanar waveguide (CPW) array antennas are proposed.They can be connected with conductor backed CPW circuits more conveniently than the microstrip arrays because no transition is needed for the CPW feeder. The completely printed structure matches the requirement of MIC/MMIC up to millimeter wave frequencies, the grating lobes can be prevented by means of limiting the spacing between elements. Their performances are experimentally investigated at the Q-waveband. The transition between the CPW antenna and the testing waveguide are discussed.
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The idea of a "phase-centre" for a feed antenna is frequently used when designing a system to be fed by the antenna. The phase-centre is loosely thought of as the point from which the beam emanates but that will be uniquely defined only for a beam which has a truly spherical phase-front and that is rarely the situation with a feed antenna, even in the far-field.
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A very staightforward method has been developed to apply space-charge resistance measurements for determining the high-field drift velocity of electrons in GaAs. The breakdown voltages of the single-drift flat-profile IMPATT diodes used in these measurements justify the validity of well known ionization rates for still higher electric fields.
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In the present work the computer-controlled Ka-band large bandwidth noise signal source is examined. The block diagram of the source construction and its functional possibilities are discussed. The results of experimental examination of its functioning are presented.
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Microwave and mm-wave circuits as well as high speed digital circuits are becoming more and more complex. Therefore in this contribution, the well known spectral domain method for planar microwave structures is extended to the analysis of an arbitrary number of dielectric and metallization layers. The metallization patterns include single and coupled strip and slot lines as well as single and coupled strip and slot resonators. This allows the calculation of a wide range of complex transmission line arrangements and - including resonator methods - of complex multilevel discontinuities. As an example, a full wave analysis of the transition between microstrip and slotline will be presented in this contribution.
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Most special purpose meteorological radars operate at millimeter wave frequencies. Those described in this paper include both ground and space based applications. Most have been built in single sets but they provide useful tools for special meteorological research.
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The selections rules for transitions between exciton (biexciton) states in crystals taking into consideration their L - T splitting are considered. It is shown that twiced number of exciton states (electroand magneto-similar), contrary to known theory, exists. The spectra of stimulated FIR radiation on excitonic transitions in CdS,previously obtained experimentally, well fit to these selection rules.
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The theory is built of a new class of elementary excitations in manyelectron atoms or molecules - spherical excitons, that consist of an electron and a hole in definite angular momentum representation. Spherical excitons may be used as effective sources of electromagnetic high orders multipole (spherical) waves.
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A review is given on ps-pulse OFID-10 μm-CO2 lasers equiped with new types of plasma shutters the plasma diagnostic of these shutters amplification of the ps 10 μm pulses with a highpressure CO2 laser amplifier the response of pyroelectric, standard and quantum-well photon-drag detectors thin-film Ni-NiO-Ni detectors submicron to these pulses as well as their analysis with Michelson autocorrelation arrangement with polycrystalline semiconductors instead of the usual single-crystal semiconductors as nonlinear media for second-harmonic generation. As a first application optical pumping of ns-pulse FIR gas-laser emissions with truncated infrared CO2-laser pulses is reported with the emphasis on superradiance. Aspects of other applications of the ps-OFID-10 μm-CO2 laser pulses and truncated hybrid-10 μm-CO2 laser pulses in atmospheric and solid-state physics are discussed.
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A Free-Electron Maser (FEM) experiment is currently underway at MIT, in collaboration with TTE (Thomson Tubes Electroniques). The purpose of the experiment is to demonstrate the operation of a FEM in the MW power range, and scalable to high frequencies and long pulses for ECRH and RF acceleration. The electron beam is produced by a 700 kV, 0.27 μperv thermionic electron gun designed and built by TTE. An axial magnetic field of 2.35 kG, produced bv 7 CW water-cooled coils, guides the beam along the interaction region. The wiggler is a 50-period permanent magnet helical wiggler, with a period of 3 cm and a linear introduction taper 10 periods long. The wiggler amplitude is 500 G. In the first stage of the experiment, we have operated the FEM as an oscillator with a TE11q mode structure in the Ka-band, at power levels of 1-2 MW and eficiencies around 5 %. We have also observed low-gain amplification of 28 and 35 GHz signals injected in the interaction region. The resonant voltages are in very good agreement with theory ; in addition, the signature of the amplified signal shows that the FEM operates in the Raman regime.
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The very short ASE OREiRL had been studied experimentally and theoretically. According to the result given in ref.[l] that, the optimum operating gas pressure of ASE OPFIRL was inversely proportional to the length of sample tube of the laser. So if the operating gas was increased to tens Torrs, then the length of the sample tube of optically pumped ASE FIR laser could be as short as several centimeters. This prediction was proved experimentally. We increased the operating gas pressure to tens Torrs, the OPFIRL lased successfully when the length of sample tube decreased to less than 5cm. The old theoretical model could hardly give correct answer for this k.nd of system. The calculated output power of OPFIRL was in the order of 10-10 W/cm2 , and the value of optimum operating gas pressure was twice as large as measured value.
Under the enlighten of experimental results, we found that the transverse feedback from the side wall of sample tube played an important role in the miniature OPFIRL. A new theoretical model of OPFIRL including transverse feedback was proposed. By using new model, the calculated optimum operating gas pressure was in good agreement with experimental value as shown in Fig.10. Sets of theoretical curves for the design of miniature OPFIRL were given.
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We have built a multiatmosphere CO2 laser amplifier with 10 mm electrode spacing for amplification of 30 ps OFID and 50 ns TEA 10 μm CO2 laser pulses. For long and short pulses we measured amplification factors of 3.4 and 10 for single and double pass injection.
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The linewidth of optically pumped FIR laser everywhere in the sample tube of OPFIRL was studied theoretically. The NH3 gas was chosen as the operating gas and three-level model was used for the theoretical calculation of the linewidth of FIR laser within the sample tube of the laser system. We found that the sample tube could be divided into three regions: A) The laser induced line narrowing region (L < 10 cm ), where the line centers of Is and Gs characteristic curve were approached with each other, so that the larger Is amplified by larger Gs and vice versa, and the linewidth of FIR laser became narrower and narrower after successive amplification in this region. B) The saturation broadening region ( Lopt < L <10 cm), where Is was large and the Gs at the line center decreased considerably due to the gain saturation effect. In this region, the gain value at the line center was less than its value at off center, so that the spectral line became broader. C) The self-absorption narrowing region ( L < Lopt). In this region the value Ip was less than its threshold value, and the molecules were not activated. The FIR signal was now interacted vith the unactivated molecular system and absorbed by the molecular system. The linewidth of FIR signal would be narrowed due to the absorption saturation effect.
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We have developed new improved plasma shutters for reproducible fast TEA-laser pulse truncation which permit reliable operation of OFID 10 μm-C02 -laser systems. Main features are low jitter and long-term stability. Designs and characteristics are discussed.
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Results are presented of an Er3+-doped CW fluorozirconate multimode fiber laser, operating efficiently at 2.75 μm, with low threshold power (< 1 mW), pumped at 650 and 795 nm, a tunable range of about 160 11m, and of a Ho3+-doped CW fluorozirconate multimode fiber laser operating around 2.9 ?m, pumped at 640 nm, with an absorbed power threshold of approx. 65 mW and a tunable range of about 120 nm. The absorbed power threshold was 35 mW when pumped at 750 nm.
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A novel optically pumped FIR waveguide laser with a glass tube which has a thin gold layer coated on the inner-wall as the waveguide has been developed.The new waveguide cavity has the advantages of having both a higher pump energy absorption efficiency and the most desirable mode for application to the FIR laser.
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High-Power CARM research at the MIT Plasma Fusion Center is described. The experimental results on a Ka-band, long-pulse CARM oscillator experiment are presented. In this experiment, a SLAC 5045 klystron gun produced an electron beam at 250-320 kV and 10-20 A; a beam α ≡p⊥/p||, variable from 0 to 1, was produced on this electron beam with a wiggler magnetic field near guide field resonance. CARM operation was observed for many parameter settings, and for frequencies ranging from 29 to 32 GHz. Output powers as high as 100 kW were achieved with an efficiency of up to 3%. Higher frequency radiation near 74 GHz was also obtained and is attributed to second harmonic CARM operation. The design of a 17 GHz CARM amplifier for application as an RF accelerator driver is presented.
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At the University of Maryland we have designed and are operating a high power two-cavity TE01 gyroklystron in the 9.7-10.0 GHz range. The target beam power is derived from a 500 kV beam with a current ranging from 120-240 A in 1 μs pulses. The target microwave parameters for this tube include a power level of 15-30 MW with a gain of 25-30 dB. The initial sequence of experiments involves characterizing a two-cavity system to address questions of tube stability and amplifier efficiency. We have completed investigations of our first three configurations and are currently examining our fourth. To date, parasitic oscillations have limited beam voltage to under 400 kV. Even with these restricted parameters, amplifier experiments have achieved powers in excess of 2 MW with gains of 17 dB and efficiencies of nearly 6%.
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The beam space-charge associated with a gyrating intense relativistic electron beam limits the current that can be propagated, and thus the ultimate gyrotron power. An experiment at NRL has investigate the use a background plasma to increase the gyrotron beam current beyond the vacuum space charge limit, and thus to permit higher power gyrotron operation.
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An 85 GHz, TE11 mode cyclotron auto-resonance maser (CARM) amplifier experiment is being planned at NRL. The experiment will use a Marx accelerator, a field-emission diode, and a 1 kW, 85 GHz Extended Interaction Oscillator (EIO). The accelerator will provide electron beam pulses with duration in excess of 100 nsec. A wiggler will be used to provide transverse momentum to the 10-100 A, 500 kV pencil electron beam. Stability against absolute instabilities is a critical issue for CARM Amplifiers. The goal of this program is to study the stability of a CARM amplifier theoretically and experimentally over a wide range of parameters.
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The induced resonance electron cyclotron (IREC) maser, a quasioptical Doppler-shifted cyclotron maser, uses a quasioptical resonator to eliminate the low frequency gyrotron modes, which are a problem in waveguide CARMs. The design of the NRL 20 MW, 280 GHz IREC maser features a 500 kV, 200 A, 1 psec pulse-length magnetron injection gun (MIG).
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A free-electron maser (FEM) experiment is currently underway at MIT, in collaboration with TTE (Thomson Tubes Electroniques). The specific purpose of the series of experiments described here is to demonstrate control of the axial mode structure of a high power FEM oscillator. In this paper, we discuss two different approach to this problem; namely, the incorporation of a cavity designed to provide mode-selectivity, and the priming of the oscillator using a 40 kW, 35 GHz magnetron.
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The extended frequency tuning range of the Strathclyde University gyrotron will be demonstrated. The gyrotron consisted of a field-immersed, field emission cold cathode and a shaped anode cavity. The cavity was oversized with an ill-defined boundary at one end. This system could therefore support the oscillation of a very large number of TEpqs modes. The maser was thus highly tunable via differential mode excitation. A heterodyne technique was used to demonstrate the maser oscillation in the Ka-band (26.5-40GHz) , with the maser oscillating at 35GHz in the TE01 mode. Previous to this, a quasi-optical diffraction grating spectrometer was used to show the maser was oscillating under different conditions respectively, single and multi-mode in the W-band (75-110GHz) and multimode in the G-band(140-220GHz). To control the output beam a quasioptical mode converter has been successfully developed. This converts various TEpq modes into a Gaussian beam. Studying the output of the maser, the mm-wave pulse has been shown to consist of a -100ns envelope containing -2ns pulses spaced -5ns apart. Although this behaviour may have several explanations, some of the most recent code simulations predict this behaviour as a result of mode beating in the complex transient start-up of the maser oscillation. With this gyrotron supporting not only many transverse modes but also several longitudinal modes, such beating is a likely consequence.
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A fixed-field analysis is presented for the harmonic auto-resonant peniotron (HARP) using a quasi-optical cavity. By solving Huygens' integral equation, the cavity is shown to support a circular polarized TEM01 mode which resonates at 95.11 GHz. By keeping a constant interaction length in the cavity and adjusting the field strength, it was found that the saturated electronic efficiency remained approximately 80 percent over a voltage range of 50 kV to 225 kV.
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Broadband operation of a gyro-TWT with a dielectric loaded waveguide is demonstrated. Fast wave interaction allows the beam quality requirements to be reduced. Self-consistent nonlinear simulation has been performed and shows that an instantaneous bandwidth of 20% with a moderate efficiency of 13% can be achieved by using a low a beam with a 2% axial velocity spread. Parameters for a proposed Ka-band amplifier are given.
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The cyclotron autoresonance maser (CARM) is shown to be a promising ECH source for heating magnetically confined fusion plasmas in the next generation tokamak, the 100 kG CIT. A 2 MW, 560 GHz, 700 kV, 7 A, TE01, magnetically tapered CARM amplifier design suitable for heating the future CIT has been developed and optimized. Analytic and numerical simulation results will be presented.
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A variety of MESFET oscillator and amplifier circuits have been fabricated and tested under optical illumination by a CW semiconductor laser. In the oscillator circuits, frequency and amplitude modulation has been observed. Response times of the devices have been characterized with the aid of a colliding pulse mode-locked dye laser.
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The theory and design of a 94 GHz quasi-optical 360 degree phase shifter is presented. The phase shifter consists of a monolithic array of Schottky diodes on a GaAs substrate. It will perform the function of electronically controlled beam steering and has additional application as an electronically controlled polarizer.
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A quasi-optical Faraday Rotator for use in beam waveguides with a frequency range of 75-100 GHz has. been developed. The rotator uses a single Samarium-Cobalt (SmCo) ring magnet and a garnet ferrite disk. Fused silica matching layers are placed at the front and back surfaces of the ferrite disk to reduce reflections at the air-ferrite interface. At the design frequency of the matching plates the measured polarization purity, or axial ratio, of the rotated signal is greater than 40 dB and the loss is less than 0.2 dB.
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Using the "MAGIC" code, computer simulation is performed to design a cathode structure which provides a radial distribution of electron beam density matching the field distribution of the TM06 mode. Thus, very narrow band TM06 mode microwave radiation can be generated in an open end waveguide. The cylinderical cathode structure consists of three pieces; a solid central piece together with two concentric rings. The radii of the two rings are determined by the radial locations of the second and third peaks of the Bessel function J0(kr). The thickness of each cathode piece and the gaps between anode slits and each cathode piece are chosen with the aid of the simulation such that the current density in the waveguide downstream of the anode slits is uniformly peaked at the peak locations of J0(kr). The simulation results show that the vircator can indeed be operated at the selected frequency 12.5 GHz with a very narrow bandwidth(Δω/ω<1 %).
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A four-port quasi-optical circulator has been designed, built and tested for operation in the millimetre wave band. The specific circulator reported here was investigated over a 20 GHz bandwidth, centred on 94 GHz. Good performance characteristics were obtained over this bandwidth. Isolations of better than 30 dB and insertion losses of around 0.5 dB were achieved. The input vswr was found to be less than 1.35 over the whole bandwidth investigated and vswr’sof less than 1.1 were achieved for narrower bandwidths. It is possible of course to configure the 4-port circulator as a 3-port circulator, or indeed as 2-port isolator. Further optimization and consequent improvements in performance are almost certainly obtainable.
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A cylindrical resonant cavity filled with an arbitrary anisotropic medium is considered. The electric displacement D and magnetic induction B are expressed within the cavity space as an expansion in terms of two solenoidal sets. The result is a matrix eigenvalue equation of infinite dimension, the eigenvalues of which are the resonant frequencies and the eigenvectors of which are the coefficients of the modal expansion. Results of computations of the resonant frequencies are compared with exact solution for some resonant structures.
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A simple, low cost three - probe microstrip circuit has been developed for S - parameter measurements of a two - port network. The results agree very well with those from HP 8510 automatic network analyzer. The design and algorithm can be easily scaled to millimeterwave frequencies.
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Plasmas can interact with a R.F. signal. We have theoretically predicted and experimentally proven that it is possible to use this interaction to shift the frequency of a fixed oscillator in free space.
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Four-port reflectometers measuring the amplitude of the reflection/transmission coefficients of waveguide structures have been realised at Ka- and W- bands. Their accuracy derived by using standard mismatches is excellent at Ka- band and fairly good at W- band. The reported reflectometers are precursors of six-port reflectometers.
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A full-wave electromagnetic approach for characterizing the electrical properties of electrical interconnects at multi-GHz, and higher frequencies is discussed. Numerical results ate presented for the coupled noise between signal pins using a typical computer hardware connector structure.
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Laser action was obtained from a small (8 cm3) far infrared laser at several wavelengths between 100 μm and 600 μm. Studies as a function of pump power, gas pressure and temperature were performed, and will be discussed.
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For a few years tunable far infrared semiconductor lasers have been available using the population inversion of light holes to heavy holes in crossed electric and magnetic fields. Their tuning range from about 70µm to 350µm make them an extremely useful radiation source in many research areas
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We used the NIST MIM diode TuFIR spectrometer in third order operation to derive center line frequencies, pressure shifts and self-broadening parameters of the J=43-42, J =44-43, J=56-55 and J=68-67 K-multiplets of the 1Σ+g ground state of CH3C14N up to K=10. Improved rotational molecular constants have been determined. The J and K-dependences of pressure shifts and self-broadening parameters are compared with theory.
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High-resolution FTIR spectra of the weak CD3-rocking bands of CD3OH and 13CD30H have been obtained. These bands lie below the strong C-0 stretching bands, and show a rather different structure. Numerous P, Q and R branch series have been assigned, from which the branch origins have been determined. The structure of the bands and the separation of n=0 and n=l branch origins indicate a substantial increase of about 31% in the torsional barrier height V3 from the ground to the CD3-rock states, but the usual energy level model does not appear to reproduce the observed branch origin patterns.
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A weak infrared band above the strong C-0 stretching band in CH3I8OH is identified as the in-plane CH3-rocking mode. Numerous P, Q and R branches have been assigned in the high-resolution FTIR spectrum. The energy level pattern in the excited state shows that the torsional barrier height increases markedly by in going from the ground to the excited state. The band overlaps well with the 9.6 μm CO2 laser band, and six CH3-rock FIR laser transition systems are identified.
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In this communication, we present data of high resolution IR Fourier Transform spectrum of 13Cd3OH. By using previously known data on 13Cd3OH, we determine the frequency and the J quantum number for the multiplets of the C-O stretch mode P and R branches. Absorbing transitions in coincidence with the frequency of C02 waveguide laser lines are also determined.
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In this communication we report new FIR Laser Lines from 13Cd3OH optically pumped by a Waveguide (WG) CO2 laser of 290 MHz tunability. For all lines, precise frequency offset measurements were performed by using the Transfered Lamb-Dip technique.
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The adiabatic analysis of the multi-level Raman far-infrared laser is carried out in the limit where the off-diagonal elements of the density matrix decay very rapidly compared to the diagonal elements. Analytic results are obtained for the gain spectrum. Applications to the high pressure limit of the NH3 and CH3F laser are discussed.
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We have designed and tested a Orbitron MASER that utilizes a quasi-optical coupled cavity. This device could be turned off by tilting (q-spoiling) one of the mirrors of the cavity. We have also operated a tuneable quasi-optical orbitron.
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A continuously tunable 12CH3F Raman FIR laser has been used to measure the high J-number portion of the CH3CI pure rotation spectrum and also a sequence of two-photon transitions in the pure rotation spectrum of 12CH3F. New FIR laser emissions from CH3CI are also reported.
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The pumped divertor1 is a major upgrade planned for the JET tokamak, involving the installation in the vacuum vessel of poloidal magnetic field coils, cryopumps and water-cooled Beryllium target plates.
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The development of a high frequency, step tunable gyrotron operating at submillimeter wavelengths and its application to a scattering measurement of plasma are described.
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Molecular gas lasers pumped by electron-beam-sustained-discharge CO2 lasers may make possible high peak power (<1 MW), long-pulse (<1 gs) submillimeter-wave sources. Such a source technology may be an attractive option to rapidly pulsed free electron lasers for small angle (<10°) collective Thomson scattering diagnostics in fusion burning tokamaks. As an example, it may be possible to build a 16 MW, 10 μs, 152 μm ammonia laser for a 7° ITER tokamak diagnostic of ion temperature and alpha-particles with a signal to noise ratio of 30 per pulse.
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In order to measure the electron desity profile on the LHD, a 10-channel laser interferometer has been designed. For the diagnostic application, an optically pumped 119-μm CH3OH laser and a discharge pumped 195-μm DCN laser are under development.
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At present time no diagnostic is available to measure magnetic fluctuations in a hot plasma. Such a diagnostic, based on microwave cross polarisation scattering, is being designed to measure magnetic fluctuations in the tokamak TORE SUPRA. The principle of the diagnostic and its implementation on TORE SUPRA are described.
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A high-temperature radiation source has been developed for the absolute calibration of diagnostic instruments for measuring electron cyclotron emission from high temperature plasmas. The source has a radiation area of Φ150 mm which is large enough to cover the spot size of the antenna radiation pattern (~Φ450 mm at the center of the JIPP T-IIU plasma) and can be heated up to 500 °C. The measured emissivity of the source is close to unity in the wavelength region between 0.5 and 5 mm.
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A physical model of obitron radiation is presented in this paper. Result of calculations according to this model agrees quite well with that obtained in obitron experiments. New ways are pointed out and new schemes are proposed fcr millimeter wave generation.
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Electron density measurements are performed on HT-6M tokamak using a 7 channel Far-Infrared HCN laser interferometer. From the measured line integrals--7 channel phase shifts the electron density profile is reconstructed by a fit procedure. Results were tested by comparison to Abel inverted.Some recent interesting experimental results were reported.
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Original waveguide shapes have been calculated by using numerical optimisation techniques which enable efficient, short tapers and mode converters to be fulfilled. Theorical results obtained for TE0m modes are discussed. An experimental study on a TE02-TE01 "taper-converter" is presented: its measured efficiency is 99.7%.
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We have presented last year, the first experimental results of our 1 MW, 8 GHz system for FRASCATI TOKAMAK UPGRADE*. Experiments have been carried out at the beginning of this year and we present in this paper extensive results of the gyrotron associated with the whole transmission line, including the 12 arms coupler divider.
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An experimental coherent pulsed radar operating at 225 GHz is described. This system uses a pulsed, phase-locked extended interaction oscillator (EIO) transmitter and an f/4 (frequency divided by 4) subharmonic mixer pumped by a phase-locked Gunn oscillator as the receiver. A quasi-optical circular polarization duplexer combines transmitter and receiver signals into the same antenna. Results obtained with this system include the detection of targets out to ranges of 3.5 km and observation of doppler spectra of trucks and tracked vehicles, including contributions from both body and wheels/tracks.
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The demand of detecting threat signals between 18 and 110 GHz has created interest in the development of broadband direction finding system at millimeter frequency range. This paper presents a novel design for direction finding system, covering frequency bands from 18 to 110 GHz. The use of flat splash reflector makes it possible to build the system without rotary joint Dual polarization detection is realized based on the design of symmetrical orthogonal-mode transducer.
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During the past few years, several new diodes have been proposed for use in frequency multipliers at millimeter and submillimeter wavelengths. Candidate diodes include a quantum-well diode, a single-barrier-varactor diode and a barrier-intrinsic-N+ diode. This paper gives an overview of these novel diodes and their potential benefits in comparison to the conventional Schottky-barrier varactor.
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As discussed in previous publication, the diode-grid array approach is attractive because a grid is monolithically integrated with thousands of solid state diodes thereby overcoming the power limitations of a single diode multiplier since the power is distributed among the many diodes making possible wattlevel CW output power throughout the millimeter-wave region.
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Metal-Si02-InP Field effect transistors (MISFETs) for the millimeter-wave systems have been analytically analyzed using a two-dimensional three-region analytical model. The surface potential and other device parameters are numerically computed. The electrical characteristics are compared with the experimental results reported in the literature for transistors operating at about 40 GHz.
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While much effort has been expended at determining the highest frequency of operation of quantum well diodes (QWD), little attention has been placed on determining the inherent maximum power available from these devices. In this paper, we report experimental results of several QWD and quantum well injection transit time (QWITT) diodes which we believe operate at their maximum output power. Simple quasi-static calculations will also be given to support this claim. From these results, extension to the higher frequency domain is possible by using available device models.
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As a candidate for compact submillimeter oscillators, we have fabricated the flux-flow oscillator (FFO) connected with a bow-tie antenna and with a SIS detector by using the Nb/AlOx/Nb tunnel junction technology. We have obtained the guarantee of exact oscillation of the FFO in the frequency range between 160 GHz and 309 GHz by means of the observation of velocity-matching steps and the photon-assisted tunneling steps.
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A new equivalent circuit is proposed and analyzed for a Voltage Controlled Oscillator in reduced height waveguide using a Gunn coupled to a varactor via two metallized discs in the waveguide H plane. The theoretical analysis which is applicable to both fundamental and harmonic oscillators is performed with computer modelling software that includes for the first time two closely interdependent double radial transmission lines. Each of the latter has as its input impedance the Gunn or varactor chip and package circuit elements.
Extensive experimental investigation applied at Ka band, of all VCO parameters including the effects of a sliding short circuit have confirmed the accuracy of the analysis. For example, a prediction of a 3.7 GHz or 13% tuning bandwidth at 28.5 GHz was experimentally confirmed. The accuracy of the analysis together with the rugged and modular VCO construction are useful for production technology of millimeter wave Gunn or IMPATT VCO's for Electronic Warfare or communications tunable local oscillator applications.
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Optical control of microwave and millimeter wave devices has attracted recent attention because of potential applications which involve the synergism of optical and microwave technologies.
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