FDTD characterization of evanescent modes-multimode analysis of waveguide discontinuities

In this paper, a finite-difference time-domain numerical dispersion relatio n for evanescent waves is derived, and its impact on the modeling accuracy is studied. The numerical evanescent constant is found to differ from the a nalytical one. As a result, a correction must be used to compute discontinu ity parameters. This influences the reference plane chosen for the analysis of propagating modes. Moreover, on calculating multimode transmission and reflection coefficients, the dispersion for evanescent higher order modes i s determinant. The dispersive relation is derived, discussed, and used to c orrect the evanescent constants for the multimode analysis of a waveguide d iscontinuity.