Wideband Dual-Circularly-Polarized Reflect-Arrays Based on Dual-Functional-Layer Cells With Berry-Phase Compensation at X-Band

International audience; We present the design and experimental validation of wideband dual-circularly-polarized (dual-CP) reflect-arrays (RAs) based on dual-functional-layered unit cells with independent control of circular polarizations. The proposed dual-CP RA cells comprise a circular polarization selective surface (CPSS) on the top based on a bandwidth-enhanced dual-meandered Pierrot structure that implements polarization selection of CP waves and a reflective half-wave plate (HWP) on the bottom. The dual-CP phase delay of the RA cells relies on the Berry-phase (BP) dictated by the rotation of the CPSS and HWP elements for achieving reflective beamforming of CP waves of opposite handedness. The diffractive properties of an infinite periodic gradient array of the dual-CP RA cells in a triangular lattice are investigated, which numerically verifies the dual-CP anomalous reflection capability. Two proof-of-concept RAs operating at X-band are designed, fabricated, and characterized. By replacing only the bottom functional layer of the RA, symmetrical and asymmetrically distributed dual-CP beams can be obtained. A measured peak gain of higher than 23.5 dBic is achieved, with a joint bandwidth of 11% for an axial ratio < 2 dB and a gain variation < 1 dB. The improved bandwidth performance, high-resolution BP compensation, and printed manufacturing process without using any metallic cavities make the demonstrated CPSS-based dual-CP RAs promising candidates for wireless and satellite communications.