Efficient calculation of modes and couplings of circular multiridge waveguide

This paper shows once more the accuracy and effectiveness of the Boundary Integral-Resonant Mode Expansion method in problems involving empty waveguides with nonstandard section and, in particular, multiridge waveguides. First, the high accuracy of the technique is proven through comparison with exact results, obtained in the case of sectorial waveguides. Then, the effectiveness of the method in the solution of discontinuity problems is shown through the example of a quadriridge dielectric-less transformer, designed to match a Faraday rotator to a circular waveguide.