Thin capacitive meshes on a dielectric boundary: theory and experiment

A rigorous formulation is used to calculate the transmission properties of a thin, perfectly conducting biperiodic capacitive mesh on a dielectric boundary. The formulation is analogous to the well-known modal method used for inductive meshes, with the modal electric fields replaced by modal currents. Measurements made at submillimeter wavelengths are presented for square capacitive meshes on a crystal quartz substrate (n = 2.1). These measurements are shown to be in good agreement with the theory. The applicability of simple equivalent circuit models is investigated and the variation of the equivalent circuit parameters with the refractive index of the substrate is discussed. A modified expression of Babinet's principle is presented which is valid in the nondiffracting region for thin meshes on a dielectric interface.