Performance Evaluation of a Passive Millimeter-Wave Imager

A cross-correlating 186-GHz passive millimeter-wave imager has been built. The key components in the signal processing hardware are two 186-GHz receivers and a broadband complex correlator. To evaluate the performance of this imager, its point-spread function, beam pattern, baseline vector, and their variations with the scanning direction have been experimentally measured and derived. Some of these results are needed for optimizing the imager's parameter settings. Others are required for implementing the modulated-beam and modulated-scene algorithms proposed in a previous paper dealing with the imager's fringe in its point-spread function. These results will also reveal any problems in the construction process of the imager. The theoretical bases for these measurements are analyzed. Novel algorithms for deriving each antenna's point-spread function and beam pattern, as well as the imager's baseline vector from the measurement results of the imager's point-spread function and beam pattern are proposed and successfully applied in the measurements. Experimental results are presented and discussed.