Modeling three-dimensional discontinuities in waveguides using nonorthogonal FDTD algorithm

A generalization of the finite-difference time-domain (FDTD) algorithm adapted to nonorthogonal computational grids is presented and applied to the investigation of three-dimensional discontinuity problems. The nonorthogonal FDTD uses a body-fitted grid for meshing up the computation domain and, consequently, is able to model the problem geometry with better accuracy than is possible with the staircasing approach conventionally employed in the FDTD algorithm. The stability conditions for the nonorthogonal FDTD algorithm are derived in two an three dimensions. Numerical results, including an H-plane waveguide junction, a circular waveguide with a circular iris, a circular waveguide with a rectangular iris, and a microstrip bend discontinuity, are presented to validate the approach