<title>Passive millimeter-wave camera images: current and future</title>

Abstract

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.

Terahertz Heterodyne Imaging Part II: Instruments

“…The few small ( 10 element) heterodyne arrays that have been realized in the submil-limeter rely on close packing individual single pixel waveguide receivers with non optimal fill-factors [5,6,7,8]. Several clever millimeter wave array systems have been constructed in W-band (generally centered around the 94 GHz atmospheric window) but all are fairly bulky and expensive [9,10,11,12,13]. Focal plane direct detection arrays are much easier to realize in this frequency range for the reasons stated, (no LO and simple DC output) and there are many viable designs from the late 1980's to the mid 1990's for submillimeter-wave array concepts developed largely for the radio astronomy community [14,15,16,17,18,19,].…”

High efficiency submillimeter-wave imaging array

“…The few small (:::;10 element) heterodyne arrays that have been realized in the submillimeter rely on close packing individual single pixel waveguide receivers with non optimal fill-factors [2]. Several clever millimeter wave array systems have been constructed but all are fairly bulky and expensive [3]. Focal plane direct detection arrays are much easier to realize in this frequency range since there is no LO and only a simple DC output, and there are many viable designs from the late 1980's and 90's for submillimeter-wave array concepts developed for the radio astronomy community [4].…”