Toward a Coupled-Dipole Formalism for Circuit Theory to Harmonize Physics-Compliant Models of RIS-Parametrized Wireless Channels

We present the first step of our efforts to derive a coupled-dipole formalism for circuit theory that ultimately aims to unify two disjoint thrusts on physics-compliant modeling of wireless channels parametrized by reconfigurable intelligent surfaces (RISs), one based on circuit theory and one based on coupled-dipole formalisms. Here, we formalize the relation between the notions of “lumped port” in the former approach and “dipole” in the latter approach. We establish that, surprisingly, two polarizability values are required to characterize a single dipole when it acts as lumped port: an “inside polarizability” perceived from inside the system and an “outside polarizability” perceived from the transmission line attached to the lumped port's outside interface. We provide an intuitive explanation as well as analytical evidence based on a model of the lumped port as a very short conducting wire with a lumped impedance at its center.