SIMULATING 3D WAVE-GUIDE DISCONTINUITIES USING A COMBINATION OF PRONYS METHOD AND FDTD WITH IMPROVED ABSORBING BOUNDARY-CONDITIONS

Two major problems usually arise when the finite-difference time-domai n (FDTD) method is used for wideband characterization of dielectric di scontinuities with high permittivity in waveguides. First, reflections are provoked by imperfections in the absorbing boundary conditions. S econdly, many time steps are necessary to overcome the problems associ ated with the truncation error inherent in the discrete Fourier transf orm (DFT). The authors present wideband absorbing boundary conditions (ABC) that have been designed to provide optimal behaviour for the ana lysis of waveguide devices. As an alternative to the classical fast Fo urier transform (FFT), Prony's method is used to process the data prov ided by FDTD in order to obtain the frequency parameters. It was found that this alternative method significantly reduces the CPU time neede d to characterise the different devices. The improvements obtained are clearly shown by analysing different dielectric discontinuities in wa veguides. The results are compared both with those given by the classi cal FDTD-FFT method and with those provided by the finite elements met hod in the frequency domain.