On the modal spectrum of the channel waveguide

The modal spectrum of the channel waveguide, that is a rectangular waveguide without one of the side walls, is studied, including higher-order modes. Both cases of the flanged structure and of the open-ended one are considered, solving the characteristic equations in the complex plane. The analysis is of interest for the understanding of recently noticed coupling phenomena in leaky-wave antennas and in shielded planar structures, and for applications to microwave hyperthermia.