Electromagnetic Model of Reflective Intelligent Surfaces

We present an accurate and simple analytical model for the computation of the reflection amplitude and phase of Reflecting Intelligent Surfaces. The model is based on a transmissionline circuit representation of the RIS which takes into account the physics behind the structure including the effect of all relevant geometrical and electrical parameters. The proposed representation of the RIS allows to take into account the effect of incidence angle, the mutual coupling among elements, the effect of the interaction of the periodic surface with the RIS ground plane. It is shown that, by using the proposed approach, it is possible to maximize the power received by a user in a RIS-assisted link without recurring to onerous electromagnetic simulations. The proposed model aims at filling the gap in the design of RIS assisted communications algorithms that are usually disconnected from physical implementation issues and realistic performance of these surfaces.