Design of a passive millimeter-wave imager used for concealed weapon detection BHU-2D-U

A passive millimeter-wave imager BHU-2D-U is introduced for detecting concealed weapons on human body. It is a subsequent model of BHU-2D. The improvements of BHU-2D-U over BHU-2D are introduced. Firstly, the field of view (FOV) of the new imager is enlarged and an U type antenna of array is adopted for whole body scan. Secondly, the enlarged FOV requires smaller antenna spacing and compact receiver arrays. The I/Q demodulators operating in double side band mode is proved for no mirror-image. In order to avoid the image-reject filter between front end and IF module, this structure mode is adopted. Thirdly, the front-end circuit and IF circuit are introduced, the good consistency and the orthogonal error are obtained. Fourthly, compared with the BHU-2D, the quantity of the receiving elements is increased to 48 unites. To cope with the increase of the correlator quantity, a multiplexing technique is used in the FPGA internal layout of the correlator array unit. Finally, the design and image reconstruction algorithms are verified based on the imaging experiments on a person with concealed weapon. The initial results of BHU-2D-U have showed the effectiveness improvements.