Active millimeter-wave video rate imaging with a staring 120-element microbolometer array

Passive indoors imaging of weapons concealed under clothing poses a formidable challenge for millimeter-wave imagers due to the sub-picowatt signal levels present in the scene. Moreover, video-rate imaging requires a large number of pixels, which leads to a very complex and expensive front end for the imager. To meet the concealed weapons detection challenge, our approach uses a low cost pulsed-noise source as an illuminator and an array of room-temperature antenna-coupled microbolometers as the detectors. The reflected millimeter-wave power is detected by the bolometers, gated, integrated and amplified by audio-frequency amplifiers, and after digitization, displayed in real time on a PC display. We present recently acquired videos obtained with the 120-element array, and comprehensively describe the performance characteristics of the array in terms of sensitivity, optical efficiency, uniformity and spatial resolution. Our results show that active imaging with antenna-coupled microbolometers can yield imagery comparable to that obtained with systems using MMIC amplifiers but with a cost per pixel that is orders of magnitude lower.