Effect of problem size on PML performance in Compact-FDTD waveguide models

The numerical dispersion behavior of the Compact-FDTD method for waveguide modeling deviates quickly from that of the well known 2-D FDTD method. This presentation deals with the effect this behavior has on the performance of the absorbing boundary conditions. It will be shown that different perfectly-matched layer (PML) absorbing conditions parameters are required as the propagation constant along the waveguide axis increases from zero and approaches the unbounded wavenumber, hence designating the waveguide as electrically large. On average, an additional 20 dB outgoing wave absorption can be achieved when PML parameters are custom optimized for electrically large waveguides.