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As Passive Millimeter Wave (PMMW) imagers mature, users have located them in more and more challenging locations. Because PMMW systems typically use natural sky coldness as a contrast source, indoor installations can become problematic. A number of semi-active illumination systems have been proposed, with various degrees of success. A problem many of them suffer from is reversed contrast -the illumination source is considerably hotter than the ambient scene, causing the cameras to act in unexpected ways. The relatively narrow extent of the illumination source is another problem, with speckle and glint often dominating the image.There are a number of unintended illumination sources in indoor locations, and all are poorly understood. This paper will examine several of them, as well as their polarametric properties, and discuss their effects on image quality.

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Rapidly improving technology is transitioning current laboratory images into reality with fielded systems expected within two years. W-band radiometers have been shown to be effective in detecting metallic and non-metallic weapons concealed under heavy garments in both outdoor and indoor situations. Systems that are in development will provide real-time display and weapon detection in controlled situations. The incorporation of technology improvements that have already been demonstrated will double the sensitivity and provide affordable systems with mpid scanning for general use.Lockheed Martin and Intelligent Machine Technology are working to build a demonstration system for the Department of Justice and the Air Force Research Laboratory that can be extended to take advantage of rapidly moving semiconductor improvements. Our current radiometer modules use a PIN switch for the Dicke calibration function followed by multiple low noise amplifier stages, a Schottky detector and a video amplifier. Sensitivity of such modules is primarily a function of the insertion loss and noise figure of the front end MMIC circuits. Processing improvements at Lockheed Martin and refined chip design will result in a 3 dB improvement in the effective noise figure within the next year. Imaging is also greatly improved by achieving greater effective bandwidth and higher operating frequency. Whereas present modules operate from 80 to 90 G Hz, MM1C improvements will provide for operation up to 140G Hz with a doubling of the bandwidth in the near term. Receiver operation up to 540G Hz has also been demonstrated at other labs. SYSTEM DESIGNLockheed Martin is developing a system that combines a linear array with rapid scanning to achieve real time detection of concealed weapons. Two 1 X 17 arrays of radiometer modules are configured with horn antennas to produce an image consisting of 34 X 44 pixels. A special Cassigrain system is used to collect the W-band energy over a 12 by 9 degree field of view. This arrangement is designed to operate at distances of 10 to 40 feet. An JR camera is provided to locate suspects in dark conditions and to provide information for background elimination so that only detection candidates associated with a suspect's silhouette are considered.

Passive imaging for security and other applications has reached an important level of development. Ka and W band imaging systems are now commercial products, thanks to cheap and stable amplifiers. While deployment numbers are still modest, improvements to these systems will come from engineering and algorithm development, and not fundamental research. What research should focus on are system volume reduction and resolution improvements.Fundamental research has several potential paths to solve these problems. Silicon Germanium CMOS can build acceptable millimeter wave amplifiers, and while SiGe noise figure is higher than GaAs, the ability to integrate RF and back end processing will push us closer to a CCD-like sensor. Antimony Arsenide features higher mobility than GaAs, with very low flicker noise and operation above 200 GHz which will reduce aperture size for equivalent resolution. More focus is needed in material characterization, particularly for clothing and common commercial materials.Finally, Sparse Array technology may build flat, conformal structures with high resolution and relatively low detector count. This paper will briefly discuss the time line of past innovations, and explore the advantages and challenges of the new technologies that will drive this field forward.