Wideband Ultrathin Retrodirective Metasurface Based on Anisotropic Unit Cell

A novel wideband ultrathin planar retrodirective metasurface (RMS) is proposed. The structure is composed of anisotropic wideband retrodirective unit cells (WRUs), achieving retroreflection of the TE polarized wave from 6.8 GHz to 8 GHz at 30∘ of incidence. Each WRU is composed of a stack of patches separated from one another by thin dielectric substrates, and the entire structure supported by a ground plane. The bandwidth of retroreflection can be optimized by adjusting the patches in the WRUs to form a low-profile RMS. The equivalent circuit (EQC) model of the proposed WRU was established, providing a fast and efficient method for analyzing the wideband performance of the WRU. Additionally, at incident angles in the 25∘-35∘ range, the proposed RMS still achieves a relatively wide bandwidth of retroreflection, with the 3 dB bandwidth depending on the incident angle, providing greater opportunities for practical applications of the RMS. As a proof of concept, a prototype composed of six supercells was designed, fabricated, and tested, with a supercell consisting of 22 WRUs. Both full-wave simulation and experimental results demonstrate that the proposed RMS achieves a relatively wide bandwidth of retroreflection at incident angles in the 25∘-35∘ range. At the nominal incident angle of 30∘, the measured results show that the RMS achieves retroreflection within 16.2% fractional bandwidth, with an overall thickness of only 0.049λ.