  This paper explores the mutual coupling in the reconfigurable intelligent
surface (RIS)-aided communication. Despite the existence of several mutual
coupling-aware models for RIS-aided communication, a notable gap remains due to
the lack of experimental validation. This paper bridges this gap by first
introducing a novel model training approach based on the 3D full-wave
simulation and subsequently validating the obtained model via experimental
measurements in a 1-bit quasi-passive RIS prototype operating in the mmWave
band. Comparative analyses reveal precision in both the employed mutual
coupling-aware model and the assessed model parameters, offering a realistic
evaluation of mutual coupling in authentic RIS hardware. Utilizing the
validated mutual coupling-aware communication model, we systematically examine
the impact of mutual coupling on communication performance by adopting the
achievable rate as a performance indicator. Our results reveal that the mutual
coupling in RIS exhibits heightened significance with increased RIS amplitude
gains and showcases a frequency-dependent effect.

Signal Processing