周期的抵抗分布を持つ平板格子の一様近似式に関する検討

概要

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Surface-relief and index modulated dielectric gratings can be approximated by uniform equivalent permittivity when the periodicity is very small compared with a wavelength. In plane gratings, equivalent anisotropic effects of surface resistance will also appear when the periodicity is very small. In this paper, a versatile uniform approximation of equivalent resistance is proposed in the three-dimensional electromagnetic scattering problem of plane gratings with periodic surface resistance illuminated by linearly and circularly polarized incidence. Scattering properties are obtained by the equivalent resistance from our proposed uniform approximation. Scattering by plane gratings with various periodic surface resistance are analyzed rigorously by the Galerkin method based on the mixed form of current expansions in the spectral and spatial domains. By investigating the difference between the equivalent resistance and the numerical values corresponding to the surface resistance of plane gratings, the applicable condition of the uniform approximation is directly cleared. And the equivalent anisotropic effects of various resistance distributions are compared.