Numerical analysis of scattering by periodic apertures in conducting screens with finite thickness

Practical examples of periodic apertures in conducting screens include self-standing ground planes, frequency selective surfaces and electromagnetic bandgap structures. The paper presents an analysis of scattering from such periodic structures. Using the equivalence theorem and introducing magnetic currents, the problem of scattering from apertures in conducting screens of finite thickness is separated into the inner problem and the outer problems. The inner problem (the region inside the aperture) is treated with two different approaches. Either the aperture volume is treated as a cavity problem (full-wave analysis) or the new approximate strategy reported by J.R. Mosig (see IEEE Trans. Antennas Propag., vol.52, p.2109-17, 2004) is used to replace the cavity by a 2D object which corresponds to the cross-section of the cavity. The two outer problems (outside the aperture) are treated by applying the mixed potential integral equation (MPIE). Since the method of moments (MoM) analysis is more complicated and time consuming due to the slow convergence of the periodic Green´s functions, the Ewald method is used as a powerful means to evaluate the free-space periodic Green´s function efficiently (Jordan, K. et al., J. Computational Phys., vol.63, p.222-35 1986).