TRW has developed a new passive millimeter wave camera for the Navy using its unique Millimeter Wave Monolithic Integrated Circuit (MMIC) technology. It operates as a pushbroom or scanning imager and can be utilized for missions that do not require as rapid a frame rate as in video-rate imagery. It is designed as a large-aperture, wide-field-of-view camera. Its focal plane consists of two rows of MMIC-based direct detection receivers and provides full sampling of the imaged scene.

We describe a system for detection of concealed weapons based on imaging the millimeter-wave reflectance contrast between the weapon and the human body. An architecture based upon pulsed illumination and gated integration has a large advantage in sensitivity over chopped CW illumination and synchronous detection. A simple sensitivity estimate based on an assumed range of 8 m, a 30 Hz frame rate, a primary collection area of 30 cm diameter, and an overall optical efficiency of 50 percent, yields a noise-equivalent reflectance difference of 0.66 percent in a single frame. The uncooled niobium micro bolometers provide a measured noise-equivalent power of 100 pW/Hz^1/2 and a time constant of 175 ns, well matched to the source pulse width and the system sensitivity requirements. Optical coupling is provided by resonant slot-ring antennas, distributed in a focal plane array covering a single 75 mm diameter wafer. The optical and electrical systems used for coupling signals into and out of the focal plane array are also described.

The US Army Research Laboratory has developed a 93-Ghz Stokes radiometer that is currently being used to quantify the polarimetric signature of various objects and materials. Preliminary measurement using the radiometer have been made of various terrain types and objects, which have included an asphalt aircraft runway, a gravel road, water, grass a tank, and a truck. A description of the development of the radiometer, its performance, and some initial results are presented. These results are the first step in assessing the utility of polarimetric radiometry and specifically how missions can be enhanced using this information. The results show that polarimetric radiometry may be useful for eliminating water as a false target in the imagery. It is also shown that asphalt aircraft runways do have a polarimetric signature that is different than short dormant grass at a 3-deg glide slope angle.

It has been known for some time that millimeter waves can pas through clothing. In short range applications such as in the scanning of people for security purposes, operating at Ka band can be an advantage. The penetration through clothing is increased and the cost of the equipment when compared to operation at W band. In this paper a Ka band mechanically scanned imager designed for security scanning is discussed. This imager is based on the folded conical scan technology previously reported. It is constructed from low cost materials such as polystyrene and printed circuit board. The trade off between image spatial resolution and the number of receivers will be described and solutions, which minimize this number discussed.

Rotman lenses offer a compact, rugged and reliable means of forming multi-beam staring array sensing arrangements. The successful implementation of Rotman devices, that operate at mm-wave frequencies, is important to a wide range of applications ranging from covert military operations and collision avoidance in cars and boats in poor weather, to landing aids for aircraft. This paper discusses the development of a Ka-band microstrip-based Rotman lens that is to be used in collision avoidance and other military related roles.

Slot-ring antennas with plane backshorts designed for operation at 95 GHZ have been fabricated and their properties measured. Using optical lithography, we fabricated the slot-ring antennas, along with integrated niobium thin-film bolometers, on dielectrically thin silicon substrates. We have performed a theoretical analysis of the slot-ring antennas with planar backshorts and compared the theoretical results with our measured beam patterns. The measured antenna patterns have highly circular main beams with full -3 dB beam widths of 21. The patterns have low sidelobe levels of about -15 dB in the H-plane and below -25 dB in the E-plane and a directivity of 17 dB. We are investigating a focal-plane array of slot-r9ng antenna- coupled bolometers for use in a concelaed-weapons imaging system.

The research and design of an active millimeter-wave concealed object imaging system is described. Several illumination and detection methods were analyzed via computer simulation to assess the effects of system parameters on the signal-to-noise ratio of the detected signal. The results of many of these simulations were experimentally verified using either a 10 MHz or a 100 GHz measurement system. Based on this assessment, two design using pulsed illuminate with gated detection were selected for development. Pulsed illumination is provided using a pulsed broadband noise source. For detecting the reflected noise pulse, two methods were examined, one using micro bolometers and the other using electrooptics. Based on imaging system considerations, such as cost of manufacture, ruggedness, etc., and technical parameters, micro bolometer arrays were selected for further development. The electronics interface, including image display capability, was developed. We examined the absorption of some common clothing materials at 100 Ghz and compared this to results previously reported.

A prototype ultra low temperature cryogen free refrigerator has been developed at the Mullard Space Science Laboratory that may be coupled to ground based cryo-coolers or space cryo-coolers. Enabling such detectors to be used, in which the fact that the detector is at very low temperature is of little concern. A development system has ben constructed as proof of consent for two space based refrigeration systems, one of which is under construction. The developed system and subsequent systems provide a compete turnkey refrigeration system for cryogenic detector cameras. The refrigeration system may be utilized in either static or in moving environments, for example vehicles, aircraft or satellites, since the power consumption is low between 24 and 224 Watts and masses are in the region of 50-90 Kg, depending on the system.

This paper reviews incoherent detection polarimetry as use din passive millimeter wave imaging. The Stokes' parameters are discussed together with the information content contained in polarimetric passive millimeter wave images. Experimental polarimeter data is presented and used to generate images of the Stokes' parameters. The degree of polarization is calculated from the experimental dat and presented. Passive millimeter wave images maximized for emission and reflection are generated from the experimentally determined Stokes' parameters.

A non-linear image restoration method has been developed by combining the advantages of the existing Lorentzian and Wiener filter techniques. It sharpens edges without introducing Gibbs ringing and restores the background without flattening it. An image is separated into features and background regions, the features are restored using the Lorentzian method and the background is sharpened using a Wiener filter. The Wiener filter is applied to the second derivative of the background to avoid ringing introduced by discontinuities where feature shave been removed. Also three pre-processing techniques are described that suppress fixed pattern noise, temporal noise and scan-lines from video data. The fixed pattern noise is suppressed by subtracting one frame of a moving image from another. Then the difference image is deconvoled with a function based on the translation of the image between each frame. Temporal noise is suppressed by calculating the displacement between frames and averaging the frames in their displaced position. Scan- lines are suppress by blurring the image in a direction perpendicular to the scan-lines and fitting the original image to the blurred image by adjusting gains and offsets. Examples of each method are provided.

Imagery data acquired from Passive Millimeter-Wave (PMMW) radiometers have inherently poor resolution due to limited aperture dimensions and the consequent diffraction limits thus requiring processing by a sophisticated super- resolution algorithm before the images can be used for nay useful purposes such as surveillance, fusion, navigation and missile guidance. Recent research has produced a class of powerful algorithms that employ a Bayesian framework in order to iteratively optimize a likelihood function in the resolution enhancement process. These schemes, popularly called ML algorithms, enjoy several advantages such as simple digital implementation and robustness of performance to inaccurate estimation of sensor parameters. However, the convergence of iterations could in some cases become rather slow and practical implementations may require executing a large number of iterations before desired resolution levels can be achieved. The quality of restoration and the extent of achievable super-resolution depend on the accuracy and the amount of a prior information that could be utilized in processing the input imagery dat. Projection-based set- theoretic methods offer a considerable flexibility in incorporating available a priori information and hence provide an attractive framework for tailoring powerful restoration and super-resolution algorithms. The prior information, which is used as constraints during the processing, can be derived form a number of sources such as the phenomenology of the sensor employed, known conditions at the time of recording data, and scene-related information that could be extracted from the image. In this paper, we shall describe a POCS approach to image restoration and use it to enhance the super-resolution performance of ML algorithms. A new algorithm, termed POCS-assisted ML algorithm, that combines the strong points of ML and POCS approaches will be outlined. A quantitative evaluation of the performance of this algorithm for restoring and super- resolving PMMW image data will also be presented.

The spatial resolution of under sampled or diffraction limited images can be improved through micro scanning and super-resolution technologies. The objective of this Air Force Phase Ii Small Business Innovative Research was to develop and demonstrate real-time or near real-time micro scanning and super-resolution algorithms using passive millimeter wave imagery. A new super-resolution algorithm based on expectation-maximization was developed which is insensitive to missing data, incorporates both positivity and smoothness constraints, and rapidly converges in 15 to 20 iterations. Analysis using measured data shows that the practical resolution gain that can be expected using this algorithm is less than a facto of two. A new micro scanning algorithm was developed and demonstrated that can reliably detect less than one fifth of an IFOV displacement using field test data. The iteration of the super-resolution and microscanning algorithms was demonstrated and resolution gains of four to six times can be achieved if the image is under sampled by a factor of two or three. Consequently, it makes sense to use a wide under sampled FOV sensor in which high spatial resolution can be obtained as desired using micro scanning and super-resolution techniques.

In the present paper the algorithms of optimum handling of fields of own radio thermal radiation are synthesized and the outcomes of researches of behaviors of limiting errors of measurement of parameters of petroleum films. These data can be received at the rate of potential exactitudes, defined by Rao-Kramer's inequality or diagonal elements of covariance matrixes of errors, inverse information matrixes Fisher.

W-band radiometers have been shown to be effective in detecting metallic and non-metallic weapons concealed under heavy garments in both indoor and outdoor situations. With a real time-time MMW camera, we now may display subjects with weapons in both indoor and outdoor situations. The system consists of a linear array of W-band detectors in a 12 inch Cassegrain system with a mechanical scanner along with support and display hardware.

High-resolution passive millimeter wave imaging cameras require per pixel detector circuitry that is simple, has high sensitivity, low noise, and low power. Detector diodes that do not require bias or local oscillator input, and have high cutoff frequencies are strongly preferred. In addition, they must be manufacturable in large quantities with reasonable uniformity and reproducibility. Such diodes have not been obtainable for W-band and above. We are developing zero-bias square-law detector diodes based on InAs/Alsb/GaAlSb heterostructures which for the first time offer a cost-effective solution for large array formats. The diodes have a high frequency response and are relatively insensitive to growth and process variables. The large zero- bias non-linearity in current floor necessary for detection arises from interband tunneling between the InAs and the GaAlSb layers. Video resistance can be controlled by varying an Alsb tunnel barrier layer thickness. Our analysis shows that capacitance can be further decreased and sensitivity increased by shrinking the diode area, as the diode can have very high current density. DC and RF characterization of these devices and an estimate of their ultimate frequency performance in comparison with commercially available diodes are presented.

Criteria are specified for deciding on whether or not elements of a digital image are resolved, and metrics are defined for the extent of the improvement, if any, in that resolution brought about by image processing. These criteria and definitions enabled a quantitative comparison of the resolution brought about by image processing. These criteria and definitions enabled a quantitative comparison of the resolution improvement in simulated images of a two-squares pattern that were processed by the linear Two-Mu algorithm and the non-linear ML and MAP algorithms. Both non-linear algorithms had identical performances, and yielded a maximum resolution improvement of X2.4 for up to 1000 iterations, compared to an improvement of X1.9 for the Two-Mu linear algorithm. The performance of these algorithms was also compared qualitatively for the more complex, measured, passive millimeter-wave (PMMW) images of a simple metal/radar absorbing material (RAM) pattern and an extremely complex PMMW image of a military vehicle. Just as for the two-squares images, ML and MAP performed identically to each other for the complex images. In the metal/RAM images processed with ML and MAP the three RAM patches were imaged much more clearly than in those of Two-Mu at a range of 382 in. However, none of the algorithms coupled produce clear images of all three RAMs at a range of 512 in, nor did any of them yield satisfactory images of the military vehicle. The processing time for Two-Mu can be extremely short if the appropriate-size inverse filter matrix for the chosen processing parameters and the point spread function are available from a previous computation. The processing time for ML and MAP, however, is governed only by the number of iterations required, which is 1000 for the two-squares pattern image, X2.4 improvement.

The need for air-to-ground missiles with day/night, adverse weather and pinpoint accuracy Autonomous Target Acquisition (ATA) seekers is essential for today's modern warfare scenarios. Passive millimeter wave (PMMW) sensors have the ability to see through clouds; in fact they tend to show metallic objects in high contrast regardless of weather conditions. However, their resolution is very low when compared with other ATA sensor such as laser radar (LADAR). We present an ATA algorithm suite that combines the superior target detection potential of PMMW with the high-quality segmentation and recognition abilities of LADAR. Preliminary detection and segmentation results are presented for a set of image-pairs of military vehicles that were collected for this project using an 89 Ghz, 18 inch aperture PMMW sensor from TRW and a 1.06 (mu) high-resolution LADAR.

An imaging 'radarometer' mode integrates a radar with a radiometer in a manner which allows simultaneous use of a common imaging antenna. The goal of this research effort was the design of a MMW camera capable of obtaining simultaneous passive and active airborne images, in the radarometer mode. An ETU was assembled to verify the design of an Engineering Model and to determine if any significant design changes were needed. ETU flight test data is presented and discussed in terms of sensor system capabilities and the Engineering Model design approach.