A Dual-Polarized Reconfigurable Intelligent Surface With Low Cross-Polarization Based on Guided-Wave Inspired Structure

In this communication, a guided-wave inspired dual-polarized reconfigurable intelligent surface (RIS) with low cross-polarization level is proposed. The designed RIS unit cell is mainly composed of a metal patch, two 180° hybrid couplers, and two phase modulation circuits from top to bottom. The top square metal patch loaded with four parasitic strips is used to convert the incident electromagnetic wave and guided-wave to each other; the middle 180° hybrid couplers are used to differentially feed the square patch to greatly reduce the cross-polarization level; the bottom phase modulation circuits are used to modulate the phase of guided-wave by applying different bias voltages. The designed unit cell can achieve a continuous full phase modulation, with a reflection amplitude fluctuation range of less than 0.8 dB and a cross-polarization level below −27 dB at the working frequency of 4.9 GHz. As validation, an RIS sample consisting of $8\times 8$ unit cells is fabricated and measured, and the measured results are in agreement with the simulated results. By providing different bias voltages to each unit cell through a field programmable array (FPGA), the reflected beam can scan in a 2-D range of ±60° at 4.9 GHz. The proposed RIS has great application potential in the RIS-assisted wireless communication systems.