Compact Reconfigurable Intelligent Surface with Phase-Gradient Coded Beam Steering and Controlled Substrate Loss

Abstract

This paper presents a 1-bit reconfigurable intelligent surface (RIS) fabricated using a three-layer structure. It employs a manual layer stackup incorporating an optimal air gap to reduce the effective dielectric losses while using a low-cost FR4 substrate. The new design of the unit cells of the proposed RIS is outlined, with each unit cell featuring a PIN-diode-based, compact, simplified biasing network that simplifies the control circuit while maintaining distinct $0^{\circ }/180^{\circ }\pm 20^{\circ }$ phase states between ON/OFF conditions. The designed RIS is in the form of a $10\times 10$ array with a compact size of $2.9\hat{\mathbf{I}}{»}_{\mathbf{g}}\times 2.9\hat{\mathbf{I}}{»}_{\mathbf{g}}$. Additionally, a phase-gradient coding scheme is presented and utilized that achieves measured beam steering up to $\pm 30^{\circ }$ in both anechoic and noisy environments. Controlled and driven by an Arduino-cum-digital interface, the proposed RIS exhibits measured reflected wave gain enhancement of about 9\,dB over an incident wave angular range of $\pm 30^{\circ }$. Furthermore, the design is also experimentally validated by transmitting quadrature phase-shift keying-modulated symbols via the RIS-assisted wireless channel. The proposed RIS works for the range 3.38--3.67\,GHz (8.3\%), and is suitable for deployment for the 5G n78 \mbox{band (3.5\,GHz).}

10 pages, 16 figures