Spectral MoM NUFFT-Based Formulation for the Efficient Analysis of High-Order Bandpass FSSs With Tightly Packed Nonresonant Elements in Skewed Grid

This communication presents a formulation of the spectral-domain Method of Moments (spectral MoM) for the analysis of periodic multilayered structures with a number of metallized interfaces alternating patches and apertures. Edge singularity entire-domain basis functions are used to model the electric currents on the patches and the tangential electric fields in the apertures. The formulation is especially suitable to characterize high-order bandpass frequency selective surfaces (FSSs) made up of nonresonant elements. Also in this communication, the nonuniform fast Fourier transform (NUFFT) is used in the spectral MoM to cover the case of unit cells in skewed grids, which enables the analysis of nonrectangular periodic lattices with tightly packed elements. Numerical examples of the design of third-order and fifth-order bandpass FSSs are presented. The FSSs are made up of hexagonal patches and apertures arranged in an equilateral triangular lattice. Results are cross-checked against commercial software CST Microwave Studio (CST MWS), and excellent agreement is found, our in-house software being more than one order of magnitude faster than CST MWS. This CPU time saving makes the proposed formulation very convenient for full-wave optimization and design.