A Millimeter-Wave Binary Reconfigurable Intelligent Surface on a Low-Cost FR4 Substrate

In this work, a reconfigurable intelligent surface (RIS) is designed and implemented on a FR4 dielectric substrate for cost-effective fabrication to improve the electromagnetic (EM) wave propagation degradation in an indoor environment at the millimeter-wave (mmWave) frequency band from 27.9 GHz to 28.5 GHz. The proposed reflecting element is an impedance tunable slot-based structure that can provide low reflection loss and binary phase modulation. A modified analytic model of RIS based on the discrete summation of elemental complex radio cross sections (RCSs) is developed for easy RIS pattern estimation and optimization. Numerical results of RIS multi-beam patterns are presented to demonstrate its feasibility.