Enhanced MoM Analysis of the Scattering by Periodic Strip Gratings in Multilayered Substrates

The method of moments (MoM) is applied to the analysis of the scattering of a multilayered periodic strip grating by a plane wave with oblique incidence and arbitrary polarization. Although this problem has been traditionally solved by means of the MoM in the spectral domain, this is an approach which leads to the computation of slowly convergent infinite summations. In this paper, the problem is solved by means of the mixed potential integral equation (MPIE) formulation of the MoM in the spatial domain. While applying the MoM in the spatial domain, two improvements are introduced which lead to important CPU time savings. First, the multilayered periodic Green´s functions are accurately interpolated in terms of Chebyshev polynomials. Second, half the integrals involved in the computation of the MoM matrix entries are obtained in closed form. As a consequence of these two improvements, the spatial domain version of the MoM presented in this paper turns out to be between one and two orders of magnitude faster than the conventional spectral domain version when basis functions that account for edge singularities are used in the modeling of the current density on the metallizations.