Analysis of periodic structures via a time-domain finite-element formulation with a Floquet ABC

An accurate absorbing boundary condition (ABC) is presented for three-dimensional time-domain finite-element (FEM-TD) analysis of infinitely periodic structures. The proposed ABC serves to truncate the computational domain in the nonperiodic directions and it is highly effective to absorb both the fundamental and the higher order Floquet modes. The formulation is applicable both for scattering and radiation analysis. Validation results are presented that demonstrate the ability of the FEM-TD to obtain highly accurate results over a broad frequency band that includes frequencies where a higher order Floquet mode is propagating (nonevanescent).