A Study of Uniform Approximation of Equivalent Impedance Sheet
for Parallel Metallic Gratings

Abstract

It is well known that dielectric gratings with very small period can be analyzed by approximation of equivalent uniform permittivity. Metallic gratings with small period must be approximated by an equivalent sheet of surface impedance. In this paper, uniform approximation of equivalent impedance is described for electromagnetic scattering problem by two parallel metallic gratings. The scattering properties are calculated by using the uniform approximate method and by using spectral Galerkin procedure. From the comparison of the numerical results, the applicable condition of the uniform approximation is discussed against wave-length normalized period.