An accurate waveguide port boundary condition for the time-domain finite-element method

In this paper, we present a generalized multimodal absorbing boundary condition formulated for three-dimensional vector TDFEM analysis for waveguide structures. The proposed boundary condition, which we refer to as waveguide port boundary condition (WPBC), is capable of perfectly absorbing both propagating and evanescent modes incident on a waveguide port with an arbitrary cross section. The formulation is based on the multimodal expansion in the frequency domain. The corresponding frequency operators are then transformed to the time domain to construct a time-domain boundary condition. The formulations for the overall TDFEM system are given and a numerical example for a waveguide discontinuity problems is presented