Planar microwave retroreflector based on transmissive gradient index metasurface

Abstract In this paper, a novel planar microwave retroreflector based on a transmissive gradient metasurface combined with a curved metal mirror is proposed and demonstrated. The transmissive metasurface can efficiently converge a wide-angle incident wave to a pre-designed curved metal mirror behind it with a proper distance, which acts as an effective reflective surface that can greatly enhance the backscattering of the incident wave with a wide-angle view. According to the full-wave simulations, the proposed metasurface retroreflector can perform an excellent retroreflective effect for incident microwaves of angle view between −30° and 30° range. A prototype was fabricated and the experimental results verify that the metasurface retroreflector can realize the monostatic radar cross section (RCS) enhancement with a continuous wide incident angle view from −30° to 30° at 10 GHz within a stable 3 dB RCS level. It is further demonstrated that the excellent wide-angle backscattering performance (absolute RCS enhancement value, operational bandwidth and/or incident angle view) of the proposed microwave metasurface retroreflector is competitive against the traditional trihedral corner reflector with comparable dimensions, thus opening up new possibilities to substitute the traditional bulky radar retroreflector by using a planar compact metasurface structure for microwave engineering. The presented microwave metasurface retroreflector is promising to develop into a low-profile, light weight and planar radar retroreflector which possesses tremendous RCS backscattering enhancement and wide-angle view operation range.