On the transformation of modal bases in rectangular waveguide

The excitation of hybrid modes by discontinuities in rectangular waveguide can often be decomposed into separate LSE/LSM or TE/TM mechanisms, so that each component can be analysed with the most suitable modal base. Correct interfacing, however, is required. We report the scattering matrices representing all the possible transformations of modal bases in rectangular waveguide. Such matrices provide an useful tool to simulate complex circuits made up of components strongly interacting, without requiring the use of a common modal base for the characterization of each element. Since the transformation matrices can easily include pieces of transmission lines, their use does not require any additional computation effort.