Single-Varactor Dual-Polarized Reconfigurable Intelligent Surface with Shared-Bias Analog Tuning

Abstract

Reconfigurable intelligent surfaces (RISs) can modify a propagation environment using electronically controlled reflecting cells. This paper presents a 5.4-GHz dual-polarized RIS, characterized over 5.0–5.5 GHz, in which one shared-bias varactor per cell tunes two orthogonally oriented resonant layers. The simulated co-polarized response provides an analog phase span of approximately 250◦. A two-mode Floquet analysis evaluates the polarization-resolved co- and cross-polarized reflection magnitudes and separates cross-polarized leakage from dissipation. Across three representative states, the simulated co-to-cross discrimination is 12.0–13.9 dB, 84.1–96.6% of the incident power is reflected when both polarizations are counted, and absorption is 3.4–15.9%; loss-disabled comparisons identify varactor series resistance as the dominant represented dissipative sensitivity. Unit-cell measurements were also performed in a single-mode WR159 waveguide for three representative capacitance states. A 6 × 6 prototype was subsequently tested in two proof-of-concept fixed-receiver experiments. Genetic algorithm optimization improved |S21| between two horn antennas, and the single retained SNR trajectory for each horn orientation showed an approximately 2 dB within-run rise. The work demonstrates low-complexity, shared-bias analog field control, and link optimization, while the common control variable does not provide independently selectable TE and TM phase states.