FAST EVALUATION OF MODAL COUPLING-COEFFICIENTS OF WAVE-GUIDE STEP DISCONTINUITIES

This letter presents a fast method for the determination of a large nu mber of coupling coefficients of a step discontinuity between a rectan gular/circular waveguide anti a smaller one of arbitrary shape. The mo de spectrum of the small waveguide is calculated by a fast algorithm-p resented some years ago-and the coupling coefficients are obtained at almost no extra cost by post-processing some of the matrices already u sed for finding the modes. Tens of modes and hundreds of coefficients are calculated in a few seconds on an ordinary workstation.