A 190 Ghz Active Millimeter-Wave Imager

The design and testing of a 190 GHz imaging system is presented. The system features two beam-scanning antennas; the first transmits a horizontal fan beam and the second receives a vertical fan beam. By correlating the signals from the antennas, an estimate of the millimeter-wave reflectivity at the intersection of the fan beams is obtained. Each fan beam is scanned by rotating a small subreflector within the antenna; this simple rotation motion allows rapid scanning. The system is portable, currently approximately 0.6m x 0.6m x 2m high; the key size constraint is imposed by the 450 mm aperture length of the antennas. The imager has an angular resolution of 0.25 degrees and a field of view of 14 degrees x 14 degrees, resulting in a raw image of approximately 50 x 50 pixels. The raw image is processed using super-resolution techniques. Images will be presented which show the capability of the system to image metallic and ceramic objects beneath clothing. These images were obtained by illuminating the scene with signals from a frequency-doubled Gunn oscillator. While this paper focuses on active imaging, the system can also operate in passive mode with reduced sensitivity.