Mode transformer for hard-surface waveguides

Mode transformation effect inside a corrugated circular waveguide filled with gyrotropic material, e.g., magnetoplasma or ferrite, is considered. The corrugation is in axial direction and the depth of the corrugation is a quarter wave length forming a boundary condition equal to a hard surface (HS). It is assumed that the material is slightly anisotropic and gyrotropic. This can be achieved at certain frequency range with a proper axial magnetic field strength. The eigenwaves are elliptically polarised hybrid-mode fields, which propagate with slightly different propagation factors. This difference in propagation factors causes the mode transformation.