Scattering models for infinite periodic structures at low frequencies

Lossy 1-D periodic strip gratings and lossy 2-D periodic FSSs (frequency selective screens) and honeybombs are investigated using two models: an anisotropic half space having its optic axis in the plane of periodicity, and an infinite impedance plane having a prescribed surface impedance which is calculated using a tensor impedance boundary condition (TIBC) from the anisotropic half space of the first model. It is concluded that the anisotropic half space and TIBC models can predict, with good accuracy, the reflections at a much reduced cost for unit cell dimensions <0.1 lambda . In the honeycomb example, each angle of incidence requires approximately 30 s for computation on a Cray 2 while only a few seconds was needed on a PC for both approximate models for all angles of incidence. These models are not intended to supersede more exact numerical solutions but rather to complement the analysis in cases when quick, approximate solutions are acceptable or when optimization studies are undertaken to maximize certain electromagnetic characteristics.<>