Wideband millimeter-wave holographic weapons surveillance systems

A new wideband millimeter wave holographic imaging technqiue is under developement for use in concealed weapons detection system. This new wideband technique provides far superior images than single frequency holographic techniques on thick objects such as the human body. The wideband technique obtains fully focused images over a designated volume and provides excellent lateral and depth resolution. Using this method, a 3D volumetric hologram is gathered with a millimeter wave linear array, a mechanical scanner, and a sweep frequency tranceiver. The 3D volumetric hologram is then processed by high-speed computational processors to reconstruct the fully focused image. Two prototype wide band millimeter wave holographic arrays have been developed at the Pacific Northwest Laboratory. The two arrays consist of sequentially switched 2 by 37 Ku band (12.5-18 GHz) and 2 by 64 Ka band (26.5-40 GHz) systems which are coupled to high-speed sweep frequency heterodyne transceivers. The arrays are used to obtain volumetric imaging data at high speeds by electronically sequencing and frequency sweeping the array antennas along 1D while performing a mechanical scan along the other dimension. The current prototype system scans an aperture the size of a large human body in about one second. Extensive laboratory testing has been performed with people carrying various concealed weapons and innocuous items with both imaging arrays during the first quarter of 1995.