Angle-Sensitive Effect of Reconfigurable Intelligent Surface

Reconfigurable intelligent surfaces (RIS) are emerging technologies capable of manipulating impinging radio waves. However, most existing RIS studies use an idealized reflection model with a constant amplitude for all incident and reflection angles, overlooking the phase responses to be sensitive to the incident angle due to the unavoidable Floquet high-order diffraction inherent in the practical RIS board. Therefore, this paper proposes an angle-sensitive RIS channel model for non-ideal reflection and constructs a corresponding RIS-assisted communication prototype, based on which the coverage probability is derived to explore the impact of introducing angle factors on the overall system. Specifically, based on the surface energy flow, the reflection efficiency factor at different angles is calculated, and the optimal RIS deployment position is further deduced. To validate the angle-sensitive model, experimental measurements are conducted in both anechoic chamber and indoor environments. Additionally, an analytical framework is developed, where the reflection energy loss is considered in signal power distribution and the non-uniform RIS-reflected interference is characterized. Experimental results essentially match with the theoretical predictions, confirming the accuracy of the proposed model. Numerical simulations further reveal the adverse influence of the angle-sensitive effect on network coverage, shedding light on future RIS implementation.