Implementation of an exact modal absorbing boundary termination condition for the application of the finite-element time-domain technique to discontinuity problems in closed homogeneous waveguides

This paper proposes an exact and mesh-efficient modal absorbing boundary termination condition (MABTC) to the Galerkin weighted residual finite element time domain (FETD) modeling technique. The developed boundary-condition formulation is specific to closed homogeneous waveguides. Two-dimensional parallel-plate waveguide problems are considered for which the MABTC, at the waveguide ports, is obtained by the convolution of the modal characteristic impedances with the modal profiles of the waveguide modes following an inverse Laplace transform. A time-truncated approximate version of the MABTC is also presented, which results in a more efficient memory and time FETD implementation (compared with the FETD code without the approximation) for the exact electromagnetic analysis of microwave circuits. Very good agreement between FETD-MABTC and finite-element frequency-domain results is demonstrated.