Reradiation and Scattering from a Reconfigurable Intelligent Surface: A General Macroscopic Model

Reconfigurable Intelligent Surfaces (RISs) have attracted attention in the last year for their characteristics of nearly-passive, thin structures that can dynamically change their reflection or refraction behaviour, and therefore realize anomalous reflection, focalization, or other wave transformations, to engineer complex radio propagation environments. Evaluating the performance and optimizing the deployment of RISs in wireless networks need physically sound frameworks that account for the actual characteristics of engineered metasurfaces. In this paper, we introduce a general macroscopic model for the realistic evaluation of RIS scattering, based on its decomposition into multiple scattering mechanisms and aimed at being embedded into ray models. Since state-of-the-art ray models can already efficiently simulate specular interactions (reflection, diffraction) and diffuse scattering, but not anomalous reradiation, we complement them with a Huygens principle approach and two possible implementations of it. The different scattering mechanisms are combined through a suitable power conservation equation. Notably, multiple reradiation modes can be modeled through the proposed approach. In addition, we validate the overall model's accuracy by benchmarking it against several case studies available in the literature, either based on analytical models, full-wave simulations, or experimental measurements.