PERFECTLY CONDUCTING LAMELLAR GRATINGS - BABINETS PRINCIPLE AND CIRCUIT MODELS

We consider rigorous modal formulations for the diffraction of plane electromagnetic waves of infinitesimally thin, perfectly conducting strip gratings. The formulations that are considered involve either modes for expanding fields in the gaps between conducting strips, or for expanding the currents flowing on their surfaces. We express the rigorous diffraction solutions in terms of simple equivalent circuit models and derive a generalized form of Babinet's principle applying to strip gratings on dielectric substrates. Matrix methods are used to simplify derivations and to exhibit explicitly interesting properties relating to the conservation of energy and phase constraints.