FLEXIBLE COMPACT HIGH-ORDER FD-FD ALGORITHM FOR COMPUTING MODE FIELDS OF MICROWAVE WAVEGUIDES WITH REGULAR AND REENTRANT CORNERS

We present a highly accurate frequency-domain finite-difference algorithm for computing mode field solutions of microwave waveguides with regular and reentrant corners. Based on FBS (Fourier-Bessel series)-derived 3-by-3 compact coefficients, our method allows for a flexible layout of the 2-D uniform grids so that distance from the waveguide boundaries to the adjacent unknowns can be arbitrary. Fourth to sixth-order convergent rates of the proposed coefficients are verified by resonancefrequency error analysis for rectangular microwave waveguides for both TE/TM polarizations. We also study the first four Neumann/Dirichlet eigenvalues of the L-shaped MW-WGs calculated by the flexible scheme, and the Neumann results are reported for the first time. Although our results achieve sixthorder accuracy for analytic modes, the order of accuracy is about one and a third for both fundamental TE and TM modes due to singularity around the reentrant corner.