Circular polarisation in a double-ridge waveguide

The existence of planes of circular polarisation of the alternating magnetic field in any waveguide is an important feature in its description. The main purpose is to investigate its existence in a ridge waveguide. While this structure does not support any plane of circular polarisation in its trough regions, it does support it on the symmetry plane revealed by bisecting the waveguide by a suitable H-plane electric wall. An experimental realisation of a new nonreciprocal ferrite isolator in this type of waveguide is included. The nature of the polarisation of the magnetic field at the open faces of a dielectric filler between the ridges is separately investigated using a dedicated finite element solver.