Simulating 3D waveguide discontinuities using a combination of Prony´s method and FDTD with improved absorbing boundary conditions

Two major problems usually arise when the finite-difference time-domain (FDTD) method is used for wideband characterisation of dielectric discontinuities with high permittivity in waveguides. First, reflections are provoked by imperfections in the absorbing boundary conditions. Secondly, many time steps are necessary to overcome the problems associated with the truncation error inherent in the discrete Fourier transform (DFT). The authors present wideband absorbing boundary conditions (ABC) that have been designed to provide optimal behaviour for the analysis of waveguide devices. As an alternative to the classical fast Fourier transform (FFT), Prony´s method is used to process the data provided by FDTD in order to obtain the frequency parameters. It was found that this alternative method significantly reduces the CPU time needed to characterise the different devices. The improvements obtained are clearly shown by analysing different dielectric discontinuities in waveguides. The results are compared both with those given by the classical FDTD-FFT method and with those provided by the finite elements method in the frequency domain