FDTD-Prony analysis of 3D waveguide discontinuities using improved broadband absorbing boundary conditions

A method for designing absorbing boundary conditions of diverse order is presented which allows good adaptation of the ports when problems in waveguide simulations of wideband are carried out. A criterion is shown which allows the choice of an optimum absorbing condition of a given order that minimizes the reflection coefficient in a particular frequency band. On the other hand, as an alternative to using the classical FFT method to obtain the scattering parameters, the Prony method, has been used, which has allowed a significant reduction in the number of the time steps necessary to obtain precise characterisations of the discontinuities. The improvements obtained by introducing the wideband absorbing boundary conditions and the use of the Prony method are shown clearly analysing diverse dielectric discontinuities in waveguides. The results obtained are compared both with those given by the classical FDTD-FFT method and those obtained with two different methods which operate at a fixed frequency: matching modes and finite elements in the frequency domain