Characterization and compensation of RIS scattering gain loss due to electromagnetic phase roughness

Fabrication process tolerances, mechanical deformation, temperature variation, dust accumulation are the main causes of alteration of the surface scattering response of a Reconfigurable Intelligent Surfaces (RIS). In this contribution, we study and fully characterize the reduction of the scattering gain when the electromagnetic reflection response of an RIS is not perfect as designed but affected by a random variation of its surface properties. Here, we assume unitary reflection and a random variation applied to only the phase profile. The proposed characterization, together with the wireless propagation models, allows estimating the worst achievable performances in terms of channel capacity and coverage area when a generic realistic RIS is assumed to be present in the smart electromagnetic environment. A compensative design strategy is here discussed and provided to mitigate the observed scattering gain loss.