Low Power Consumption and Beam-Sustainable Reconfigurable Intelligent Surface for Fixed Wireless Communication at Millimeter-Wave 5G Band

We present a low-power-consumption and beam-sustainable reconfigurable intelligent surface (RIS) for reliable millimeter-wave 5G fixed wireless communication in non-line-of-sight (NLOS) scenarios. Conventional RIS designs require continuous power to maintain beamforming, with power consumption divided into two main parts: power drawn by the control board and power dissipated by unit cells. The strategies for reducing power consumption differ based on the adjustable components used. In this study, a liquid crystal (LC)-based RIS is employed to achieve low power consumption, alongside a customized bias circuit that incorporates switches and capacitors. The proposed circuit operates using bias pulses, allowing charges to be stored in the capacitors, which in turn ensures beam sustainability. Moreover, owing to switches, the proposed RIS, consisting of an <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\mathrm{N} \times \mathrm{N}$</tex> array, requires only 2N bias nodes for two-dimensional beamforming, unlike traditional RIS designs. This innovative biasing approach, referred to as an active-matrix scheme, introduces a low-power-consumption, beam-sustainable RIS for the first time.