Modulated corner reflector using frequency selective surfaces for FMCW radar applications

This work describes a modulated transponder based on a corner reflector where at least one of the metallic surfaces is replaced by an actively-controlled frequency selective surface (FSS) loaded with switching PIN diodes. The reflectivity of the faces loaded with the FSS changes with the bias of the diodes modulating the radar cross-section of the corner. The transponder therefore answers the reader, modulating the backscattered field. In addition, the retrodirectivity property of corner reflectors enables the response to be distinguished from the interference of non-modulated clutter reducing multipath effects. This approach allows high values of backscattered fields to be obtained over large angle beam widths and frequency bandwidths. An experimental setup based on a commercial X-band FMCW radar is used to measure the transponders. Experimental results obtained for a dihedral corner reflector and a cross reflector transponder at several distances are provided. In the first case, a sectorial angular coverage is obtained, whereas in the second case a quasi-onmidirectional performance is obtained.