A dual-resonant coupling mechanism to overcome efficiency loss in thin-layer liquid-crystal metasurfaces

Liquid-crystal (LC)–based metasurfaces enable dynamic electromagnetic control with low power consumption, but reducing the LC thickness to improve response speed often causes severe radiation-efficiency degradation. This work introduces a dual-resonant coupling mechanism to address this limitation in thin-layer LC guided-wave metasurfaces. By combining an admittance-equivalent model with temporal coupled-mode theory, we establish a unified framework that reveals an asymptotic cubic scaling of efficiency degradation in thin LC layers and provides an effective route to enhancing radiative coupling through an auxiliary radiating structure. A parasitic patch layer is incorporated above the LC resonator to form a hybrid dual-mode system that enhances radiation while suppressing dissipation. Two 71-element metasurface prototypes were fabricated and experimentally characterized. Measurements show more than 6 dB realized-gain improvement across the operating band and an average enhancement of 8.5 dB at 27.5 GHz, while maintaining beam scanning from −60° to +60°.