Hybrid Finite Element-Fast Spectral Domain Multilayer Boundary Integral Modeling of Doubly Periodic Structures

Hybrid finite element (FE) boundary integral (BI) analysis of infinite periodic arrays is extended to include planar multilayered Green’s functions. In this manner, a portion of the volumetric dielectric region ci~n be modeled via the finite element method whereas uniform multilayered regions can be modeled using a multilayered Green’s function. As such, thick uniform substrates can be modeled without loss of efficiency and accuracy. The multilayered Green’s function is analytically computed in the spectral domain and the resulting 3 1 matrix-vector products are evaluated via the fast spectral domain algorithm (FSDA). As a result, the computational cost of the matrix-vector products is kept at O ( N ) . Furthermore, the number of Fioquet modes in the expansion are kept very few by placing the BI surfaces within the computational unit cell. Examples of frequency selective surface (FSS) arrays are analyzed with this method to demonstrate the accuracy and capability of the approach. One example involves complicated multilayered substrates above and below an inhomogeneous filter element and the other is an optical ring-slot array on a substrate several hundred wavelengths in thickness. Comparisons with measurements are included. .