Fast evaluation of modal coupling coefficients of waveguide step discontinuities

The author presents a fast method for the determination of a large number of coupling coefficients of a step discontinuity between a rectangular/circular waveguide and a smaller one of arbitrary shape, The mode spectrum of the small waveguide is calculated by a fast algorithm-presented some years ago-and the coupling coefficients are obtained at almost no extra cost by post-processing some of the matrices already used for finding the modes. Tens of modes and hundreds of coefficients are calculated in a few seconds on an ordinary workstation.