Low-Cost 3-D Millimeter-Wave Concealed Weapons Detection Using Single Transceiver Affine Synthetic Arrays

The problem of detecting concealed weapons with a low-cost 3-D imaging radar system is addressed. The concept of affine phase center translations to generate a synthetic array is proposed as an alternative to conventional synthetic aperture and multistatic imaging radars. This enables the generation of a synthetic 2-D array with a dynamic dual reflector antenna system and a single transceiver. The dual reflector antenna is composed of a 3-D printed ellipsoidal sub-reflector and a conic main reflector. The phase front of the horn feed is shown to be translated to different locations by controlling the relative positions of the two reflectors. The reflectors are fabricated using a simple protocol that keeps the cost very low but introduces significant phase aberrations. These phase aberrations are corrected by developing a novel geometrical optics based optimized calibration routine. The imaging system is tested using a 76.5–84.5 GHz stepped frequency transceiver in different concealed weapons detection scenarios. As a demonstration, a metallic handgun and a nonmetallic pipe-bomb are concealed on a mannequin which serves as a human surrogate with similar skin reflectivity. At a target distance of 2.8 m the achieved depth resolution and lateral resolution are 2 and 1.5 cm, respectively. The 3-D images constructed using back-projection are of high enough quality to successfully identify the weapons while maintaining the privacy of the individual.