An Evaluation and Modeling of Scattering Parameters of an Reconfigurable Intelligent Surface (RIS) as a Function of Incident and Reflected Angles

Recently, reconfigurable intelligent surface (RIS) has attracted continuous attention in wireless communications. As the normal incidence condition of electromagnetic waves cannot always be satisfied in practical applications, the angular sensitivity of the incident and reflected waves on the performance of such RIS needs to be assessed and modeled. In this work, the impact of incident angles on the scattering parameters has been assessed through an RIS. The unit cell of the proposed RIS consists of a square spilt-ring-resonator which is designed on an FR-4 dielectric substrate with a ground plane at the back. Two horn antennas operating in the X-band are used as a transmitter and receiver antennas for assessing the scattering parameters. For different incident angles, simulation results show that the lowest insertion loss of −32 dB at 10 GHz has been achieved when the incident and reflected angles are 15° and 16.5° respectively. The proposed work is the first step to develop a theoretical model to determine the optimum receiver position for arbitrary incident angles as the main challenge in designing RISs is to obtain their electromagnetic (EM) responses, which is time-consuming and computationally prohibitive.