It is well known that millimetre wave systems can penetrate poor weather and battlefield obscurants far better than infrared or visible systems. Thermal imaging in this band offers the opportunity for passive surveillance and navigation, allowing military operations in poor weather. We have previously reported a novel real time mechanically scanned passive millimetre wave imager operating at 35GHz and in this paper a 94GHz variant will be described. This 94GHz imager has a field-of-view of 60° x 30° and has diffraction limited performance over the central two thirds of this field-of-view. It is relatively inexpensive because the scene is imaged using a linear array of direct detection receivers and compact folded optics. The receiver array has been constructed using indium phosphide monolithic microwave integrated circuits (MMICs) allowing high gain and low noise figure to be achieved. The compact optics consist of a polarisation sensitive mirror and a Faraday rotator. readily The mirror is constructed from expanded polystyrene, supporting a printed copper grid etched onto a PTFE/glass fibre substrate. These materials are low cost and readily available. The Faraday rotator is made from a commercial grade plasto-ferrite sandwiched between antireflection coatings. The optics produce a conical scan pattern and image processing is used to generate a raster scan pattern and to perform gain and offset corrections.

Passive millimeter-wave (MMW) imagers have the potential to be used on low-flying aircraft for terrain-following / terrain-avoidance during low-visibility conditions. This potential exists because of the inherent nature of MMW radiation that allows it to penetrate many visible and IR obscurants such as fog, clouds, and smoke. The phenomenology associated with this application, however, has not been fully explored. Specifically, the radiometric signatures of the various obstacles that might be encountered during a low-altitude flight need to be thoroughly understood. The work described in this paper explores the 93-GHz passive signature of a deciduous treeline and a concrete/glass building. The data were taken from the roof of a 4-story building to simulate the view of a low-flying aircraft. The data were collected over many months with an ARL-built Stokes-vector radiometer. This radiometer is a single-beam system that raster scans over a scene to collect a calibrated 93-GHz image. The data show the effects of weather and tree lifecycle on the 93-GHz brightness temperature contrast between the horizon sky and the obstacles. For the case of trees, it is shown that the horizon sky brightness temperature is greater than that of the trees when the leaves are on because of the reflective properties of the leaves. This made the trees quite detectable to our system during the late spring, summer, and early fall. Concrete buildings are inherently low-contrast obstacles because their vertical nature reflects the horizon behind the sensor and can easily mimic the forward horizon sky. Solar loading can have a large effect on building signatures.

As a result of its relatively short wavelength coupled with relatively high penetration of such things as fog, bad weather and clothing, millimeter-wave imaging provides a powerful tool for both airborne and security type applications. By using a passive approach such as that implemented here, it is possible to image through bad weather or detect concealed weapons and articles all without generating any form of radiation that might either help an enemey or raise health concerns. In this paper we will show imagery from our second generation state-of-the-art unit and discuss the technology involved.

Mm-wave imaging has high potential for all weather performance but requires large apertures to acheive acceptable spatial resolution. These large apertures need to collect radiation from a range of angles in the field of view and form a two dimensional image. The ideal method for achieving such an image would be to have an aperture completely filled with receivers and to electronically beam-form. Unfortunately this technology is not sufficiently developed at present to make this a practical propostion. Receivers are far too expensive to form a completely filled aperture and the technology of beam-forming is still under development. The alternative and most cost effective solution at present is to have a comparatively small number of receivers and scan them across the scene using an opto-mechanical scanner. In scanned thermal imaging systems it is usual to employ high speed rotating polygons to perform the line scan and a flapping mirror for the framing motion. The pupil size is typically 10mm in thermal imaging and the polygons are 40mm in diamenter. If such an arrangement were used at mm-waves where the pupil size is of the order of 1m, the rotating polygon would be 4m in diameter. The paper describes new compact opto-mechanical systems based on rotating discs, prisms and using frequency and polarization selective surfaces.

Trex Enterprises has developed a passive millimeter-wave imaging system incorporating a number of new technologies. The system has a pupil-plane architecture that uses a phased array, flat panel antenna and a phase processor based upon millimeter-wave optics. The production and operation of a 232-element W-band phased array and processor poses a number of technical problems including minimizing losses in the front end and adjusting the phase lengths of the processor. The system also has 192 frequency processor cards that perform real-time Fourier analysis of W-band signals over an 18 GHz bandwidth using millimeter-wave optics. Production of a suitable phase and frequency processor in large quantities that form good beams and maintain signal strength requires the adoption of new materials and design strategies. The refinement of these technologies at W-band frequencies allowed Trex Enterprises to produce an imager which is both compact and suitable for large-scale production. In this paper, we will discuss the design and production of the millimeter-wave components unique to this system architecture. We will also present the performance of these components and how they affect the performance of the millimeter-wave imager as a whole. An integrated front end is tested to determine the accuracy of the beam-forming network in producing antenna patterns.

We have developed amplifier based receivers using Indium Phosphide high electron mobility transistor (HEMT) monolithic microwave integrated circuit (MMIC) technology. These compact receivers are designed with atmospheric temperature and humidity sounding requirements in mind, operating at 100-125 GHz around the 118 GHz oxygen line, and at 160-185GHz near the 183 GHz water line, with average noise temperatures of 1600 and 1200K respectively. They are intended for applications where small volume and power consumption are critical. We will present laboratory data on the noise temperature of these receivers operated at room temperature and preliminary field data.

Passive millimetre-wave imaging provides the capability to detect objects concealed beneath clothing. In the past, this has been accomplished successfully outdoors, using the cold sky illumination to provide the majority of the scene contrast. However, many applications, such as airport security scanning, require a technology that can operate in an indoor environment. This paper describes work done to develop a safe and effective illumination source for indoor millimetre-wave imaging. Results from a prototype indoor millimetre-wave security scanner are presented, clearly showing hidden weapons and other objects.

Actively illumniated mm-wave imaging systems for concealed weapons detection offer the possibility of much higher sensitivity than with passive systems. We discuss several issues specific to mm-wave imaging systems that are actively illuminated and describe our implementation of such a system. We show that the illumination geometry is critical to the appearance and detectability of targets, and present measurements of the bi-directional reflectance distribution of a small handgun, as a prototypical target. We demonstrate suppression of standing waves using frequency modulated (FMCW) illumination and directly compare images taken with CW, FMCW, and pulsed illumination. Our implementation of an active imaging system is based on a 120-element focal-plane array (FPA) of uncooled antenna-coupled microbolometers. We describe the fabrication process and yield for these FPA's, as well as tests that show the performance of individual pixels on the 120-element array to be equivalent to that of isolated devices. These results demonstrate that wiring for readout of an antenna-coupled FPA can be made "transparent" to the antennas. Therefore, a mm-wave FPA that is read out through wiring to the perimeter of the array constitutes a simple and feasibile architecture, in contrast to the infrared, where space limitations require vertical (3D) integration of readout and FPA. The electrical readout system for the FPA is also described. Finally, we present a result obtained with the full FPA system, showing that 3-way illumination is much more effective for detection of a complex target than a single directional illuminator.

This paper reviews the feasibility and requirements of scanning passive millimetre wave imaging systems based on the latest electronic technologies. The sensitivities, bandwidths and field-of-views of imaging radiometers are examined on the basis of large numbers (several hundreds) of distributed antennas and receivers. Transfer functions and point spread functions, of minimum redundant arrays for imaging, are calculated and the effects of phase stability assessed. Possible future directions of passive millimetre imaging, enabled by the storage of pre-detection radiometric data, are highlighted..

This paper addresses the use of high resolution aperture synthesis radiometry for the purpose of reconnaissance and surveillance on an Unmanned Aerial Vehicle (UAV) platform. A short introduction to the military background for the applicability of this technique is given. The phenomenology of microwave radiometry is shortly introduced and range considerations are outlined. The principles of aperture synthesis are presented and a first design idea based on previous investigations for a low-expense system is given. Based on that the imaging performance of the system is investigated using a typical brightness temperature scene from earlier linescanner measurements at 90GHz. The array thinning, the finite sensitivity, and the impact of non-ideal flight maneuvers are discussed. It is shown, that the low-expense system is able to produce satisfying results for target detection.

Millimeter wave cameras often have limited pixel count and image uniformity problems. While these may be expected to improve as technology advances, present simple image processing algorithms can provide significant improvement in users displays. Data collected with the existing NIJ camera is shown, along with uniformity corrections, and a straightforward correlation algorithm that provides a tracking dot on a weapon. This give a threat indication on what might at first appear to be a very marginal image stream. Suggestions for future work are also presented.

In applications of PMMW imaging such as real-time video, fast restorations are needed to keep up with the frame rate. FFT-based restoration provides a fast implemention but at the expense of assuming that the regularization term is constant over the image. Unfortunately, this assumption can create significant ringing artifacts in the presence of edges as well as edges that are blurrier than necessary. Furthermore,shift-invariant regularization does not allow for the possibility of superresolution. Shift-variant regularization provides a way to vary the roughness penalty as a function of spatial coordinates to reduce edge artifacts and provide a degree of superresolution. Virtually all edge-preserving regularization approaches exploit this concept. However, this approach destroys the structure that makes the use of the FFT possible, since the deblurring operation is no longer shift-invariant. Thus, the restoration methods available for this problem no longer have the computational efficiency of the FFT. We propose a new restoration method for the shift-variant regularization approach that can be implemented in a fast and flexible manner. We decompose the restoration into a sum of two independent restorations. One restoration yields an image that comes directly from an FFT-based approach. This image is a shift-invariant restoration containing the usual artifacts. The other restoration involves a set of unknowns whose number equals the number of pixels with a local smoothing penalty significantly different from the typical value in the image. This restoration represents the artifact correction image. By summing the two, the artifacts are canceled. Because the second restoration has a significantly reduced set of unknowns, it can be calculated very efficiently even though no circular convolution structure exists.

This paper discusses the use of constraints when super-resolving passive millimeter wave (PMMW) images. A PMMW imager has good all-weather imaging capability but requires a large collection aperture to obtain adequate spatial resolution due to the diffraction limit and the long wavelengths involved. A typical aperture size for a system operating at 94GHz would be 1m in diameter. This size may be reduced if image restoration techniques are employed. A factor of two in recognition range may be achieved using a linear technique such as a Wiener filter; while a factor of four is available using non-linear techniques. These non-linear restoration methods generate the missing high frequency information above the pass band in band limited images. For this bandwidth extension to generate genuine high frequencies, it is necessary to restore the image subject to constraints. These constraints should be applied directly to the scene content rather than to any noise that might also be present. The merits of the available super-resolution techniques are discussed with particular reference to the Lorentzian method. Attempts are made to explain why the distribution of gradients within an image is Lorentzian by assuming that an image has randomly distributed gradients of random size. Any increase in sharpness of an image frequently results in an increase in the noise present. The effect of noise and image sharpness on the ability of a human observer to recognise an object in the scene is discussed with reference to a recent model of human perception.

In this paper we consider some aspects of radiovision systems.At the beginning,we examine the coherent phenomena in multisensor systems, and what benefits have the systems based on this phenomena. Later we discuss the applications of calculated antenna pattern for,multi-channel radiovision system and show,that it can be used in some tasks if experimental one is not available. In the last section we consider superresolution methods,which allow to enhance resolution of the radio-thermal images btained,and exceed the bounds of the Rayleigh limit.The results of several data processing series are provided.

It is widely acknowledged that tree roots and other forms of buried biomass have an adverse effect on the performance of ground-penetrating radars (GPRs). In this work we present experimental and theoretical work that quantifies that effect. Test sites containing extensive root infiltration at Eglin Air Force Base, FL were probed with a GPR. After completing the measurements, the sites were excavated, and the root structure and soil were thoroughly characterized. Supplemental GPR measurements of simple cylindrical objects in a laboratory setting were performed to investigate basic scattering behavior of buried roots. A numerical simulator based on the Discrete Dipole Approximation (DDA), an integral-equation-based method, was developed, validated and subsequently used to compute scattering from root structures modeled by an ensemble of buried cylinders. A comparison of the measurements and numerical calculations is presented that quantifies the potential for false alarms and increased clutter due to buried roots.

When a synthetic aperture radar, employing an ultra-wideband impulse waveform, forms an image of an area on the ground by using a backprojection algorithm, artifacts occur due to any strong reflectors in the scene. These artifacts can obscure or influence the image of the area containing low-level reflectors that may be of interest. Herein, we examine the factors of the imaging geometry that leads to these artifacts or influences and propose a procedure for reducing them. We demonstrate the artifacts and the procedure to reduce them with the data collected by the ultra wideband radar of the U.S. Army Research Laboratory.

The focus of this paper is predicting the bounds on performance of a vote-based object recognition system, when the test data features are distorted by uncertainty in both feature locations and magnitudes, by occlusion and by clutter. An improved method is presented to calculate lower and upper bound predictions of the probability that objects with various levels of distorted features will be recognized correctly. The prediction method takes model similarity into account, so that when models of objects are more similar to each other, then the probability of correct recognition is lower. The effectiveness of the prediction method is validated in a synthetic aperture radar (SAR) automatic target recognition (ATR) application using MSTAR public SAR data, which are obtained under different depression angles, object configurations and object articulations. Experiments show the performance improvement that can obtained by considering the feature magnitudes, compared to a previous performance prediction method that only considered the locations of features. In addition, the predicted performance is compared with actual performance of a vote-based SAR recognition system using the same SAR scatterer location and magnitude features.

Georgia Tech Research Institute (GTRI) was tasked by the U.S. Department of Transportation (USDOT), Federal Highway Administration (FHWA), to test the Safety Warning System® (SWS) for application as an in-vehicle communications system. In addition to the communications function, the system has a 24 GHz homodyne Doppler radar function that provides the system’s micro-controller with traffic counts and speed information on passing vehicles. One task was to use the homodyne radar to see if the resonant frequency of an 18 wheel tractor trailer could be determined while the truck was at a distance from the radar (Greneker, et al.). This led to a study of additional methods to detect low frequency resonance effects excited by the interaction between the highway and the suspension system of a tractor trailer when the body induced Doppler signal is many orders of magnitude larger than the resonance frequency of interest. This paper describes a method that the authors call the “envelope detection” method. This micro-Doppler extraction technique has proven useful to extract small vibration and resonance induced signals in the presence of a large Doppler signal from the radar energy reflected from the radiator, hood and cab of the tractor trailer used in testing.

We present a new approach to the design of deinterleavers for radar intercept receivers.We design the deinterleaver to target frequency and pulse repetition frequency (PRF)agile pulse Doppler emitters,a class of radar sources that is difficult to deinterleave with traditional approaches.Targeting this specific class of emitters al- lows us to take advantage of the coherent processing signal structure that is common to emitters in the class.The deinterleaver extracts constant pulse repetition interval (PRI) pulse packets from the receiver signal, and then clusters the pulse packets on the basis of coherency.Pulse packets that come from the same radar source form coherent signal structures,pulse packets from different sources do not. The paper describes the filtering algorithms that extract the pulse packets,presents an analysis of signal coherency that provides a priori estimate of the effectiveness of the design,and describes the clustering algorithms that separate the pulse packets into deinterleaved signal streams.

High resolution radars use wide bandwidth waveforms to create images of unknown objects. In military systems, such radar images can be used for target identification and discrimination functions as long as the time sidelobes are kept low. However, the need for low sidelobes imposes constraints on the design of the radar in general, and the signal processing in particular. Furthermore, since military radars must operate in the presence of strong interference, wideband Adaptive Beam Forming techniques (ABF), such as Space-Time Adaptive Processing (STAP), are needed. This paper describes signal processing techniques for wideband digital radars that utilize stretch processing at each receiver. It analyzes the impact of stretch ABF techniques on time sidelobes, showing how sidelobe levels depend on the ABF architecture. It describes the impact of channel errors on time sidelobes and null depth, and proposes a digital filtering architecture for channel equalization, digital beamforming, and STAP.

Trained algorithms are required for detecting stationary targets with practical real-beam radars. The parameters of these algorithms are unique to each site or clutter class. A problem arises when an algorithm trained on one clutter class is applied, perhaps inadvertently, to another class. In this case, the performance of the system can degrade to an unacceptable level. We have developed a system that adapts, online, the parameters of the algorithm to the encountered clutter type. This system consists of two neural networks - one for adapting the coefficients of the algorithm and the other for adapting the threshold level.

An ultra wide band (UWB) signal is defined as any radiation in which the 3-dB bandwidth is greater than 25% of the center frequency. UWB signals are characterized by extreme low powers and large bandwidths, which can be used for data, voice and video communication. Since UWB waveforms have very short time duration, they are relatively immune to multi-path cancellation effects. In this paper we test the performance of a simulation to model the propagation of an UWB signal in outdoor forested environment. The simulation uses a combination of Finite Difference Time Domain and ray tracing methods to simulate the UWB wave propagation. The model takes into consideration the dielectric constants of the materials of the trees and measures the signal strength for vertical and horizontal polarizations of the UWB antennas placed at various heights and distances from each other. The results of the simulation are compared to measurements obtained from tests conducted at a wooded area in Seneca Creek State Park, Gaithersburg, Maryland. It was observed that upto 150 ft distance between the transmitter and receiver, the horizontally polarized antenna system gave better signal-to-noise ratio, but at greater distances the vertically polarized antenna system gave a better signal-to-noise ration performance. Three dimensional plots of the signal strengths and the signal-to-noise ratio for various transmitter and receiver distances are plotted for the system. These are compared with experimental results and the simulation closely matched the experimental data. The results of the simulation and measurements will be used for further developing an UWB location and tracking system for outdoor environments.

PULSAR is an Ultra Wide-Band short pulse Radar developed by the CELAR (French Technical Centre for Armament Electronics) and the IRCOM (Research Institute of Microwave and Optical Communications) in order to detect foliage and ground concealed targets. One of the most promising mission of such potential radar is the detection of buried and surface land mine fields. An instrumentation measurement system has been designed and implemented. This paper deals with the recent development efforts on this system, specially on a new pulse generator and a new UWB antenna. Recently, the LGE (Laboratoire de Génie Electrique) has developed a high voltage pulse coaxial generator. These recent developments allowed to increase the pulse output voltage and the pulse rise time. The new UWB antenna is able to support a very high voltage; the bandwidth and the gain are greater than the ones of the previous antenna.

Automatic target detection (ATR) depends on the surrounding clutter as well as on the target signatures. Swiss DoD has established a measurement-platform in the W-Band frequency frame to generate the necessary data's . The wavelength of the W-Band is extreme smaller than the target dimension and the footprint of the antenna does not illuminate the entire target. This have the result, that the actual echo-signal correlates strongly to the view angle. The signature of a target is so complex for any evaluation, that it is necessary to create a statistic model with virtual scatters. As an example this model can be integrated in simulations of smart ammunition effectiveness. With data of a statistical model it is possible to: 1. to evaluate the object according its RCS. 2. to create the necessary camouflage-precaution against radar-seekers and check there efficiency. 3. Detection probabilities of a target in different clutter conditions. 4. to identify strong reflectors and thereby reduce the RCS value of the target.

In this paper a microwave Doppler-scatterometer system for a sea surface remote sensing, particularly for the determination of sea state and near surface wind speed, is presented. It is shown that there is a sense and a reason in such a system application for clear-air turbulence detection in atmospheric boundary layer, because the system allows simultaneously and by easy way to record amplitude and phase fluctuations of a radar signal reflected from turbulence.

The main computation relations for determination o MMW radar land clutter statistical characteristics are analyzed. Expressions for normalized RCS determination of different surface types and polarization features of backscattering signals are discussed. Spatial and temporal statistical characteristics of the quadrature components and the amplitudes of scattered signals are analyzed; the influence of spatial characteristics of real land terrain on the quadrature component and amplitude distributions is discussed. It is shown that the amplitude pdf is approximated by the Weibull's law and the distribution of quadrature components is described by the compound Gaussian law. The spatial distributions for different terrain types are presented. As result, the algorithms for radar clutter modeling at millimeter band of radiowaves are obtained taking into consideration the spatial statistics of natural land surface.

Detection of stationary targets with a real-aperture radar requires an algorithm that is a function of suitably defined features. The definition and values of these features are normally dependent on bandwidth, look-averaging, and polarization. Since the use of a fully polarimetric radar may not be feasible for low-cost radars on ground platforms, the goal of this effort is to investigate trade-offs between polarization and bandwidth. In this paper, we present prescreener and quadratic polynomial discriminator performance comparisons as a function of polarization, bandwidth, and look-averaging.