A simple source excitation scheme for the FD-TD analysis of waveguide discontinuities

A simple source excitation scheme for the analysis of waveguide discontinuities with the FD-TD method is proposed. In this scheme, the source plane (where only one field component is needed) is loated several nodes inside the terminal plane and the field component in the incident plane is simply corrected. Under this arrangement, the interaction between the source excitation and the reflected wave at the terminal plane can be separated in time domain. This allows us to apply absorbing boundary conditions on the terminal plane directly, without any special treatment. Moreover, the terminal plane can be located very close to, even at three nodes in front of, the discontinuity. The validity and efficiency of this scheme are confirmed by comparing the numerical results with analytical solutions for a typical discontinuous waveguide.