Chiral hard-surface waveguide mode transformer

Field propagation in cylindrical axially corrugated waveguide filled with chiral medium is considered in this paper. The depth of the corrugation is a quarter-wavelength, making a hard-surface (HS) boundary. These eigenfields inside the chiral HS waveguide are circularly polarized. In a nonchiral HS waveguide, these eigenmodes are propagating with the same propagation factor. However, for small chirality values, there exists weak coupling between the eigenfields, which results in a change in polarization of the propagating field. This effect makes it possible to make mode transformers and phase shifters. Also, the chiral HS waveguide of a proper length can be used as a matching element between different kinds of circular waveguides.