How Phase Errors Influence Phase-Dependent Amplitudes in Near-Field RISs?

Near-field reconfigurable intelligent surfaces (RISs) are unlocking promising potentials for the next generation of communications. Different from prior works that separately address phase shifts with errors and phase-dependent amplitudes (PDAs) in the RIS pixel hardware, this paper jointly studies power losses (PLs) caused by these two impairment factors. We propose three different pixel reflection models to accommodate different practical scenarios and derive their approximated upper bounds on the PL. It is important to note that neglecting uncertainties in the PDA may lead to an overestimation of the performance improvement offered by the RIS, thereby explaining the discrepancy between analytical and measurement results in several previous studies. Numerical simulations verify the correctness of the theoretical results.