An EM model of a corrugated circular waveguide polariser

Corrugated waveguide polarisers are frequently used in spacecraft reflector antenna feed systems where an optimum axial ratio bandwidth is required. Devices based on rectangular waveguides are amenable to analysis using mode-matching/S-parameter chaining techniques, but present certain manufacturing difficulties and are inconvenient for integration with circular feedhorns. The converse is true for a circular waveguide: the corrugation profile generates waveguide cross-sections that are non-circular and possibly of a shape that makes it impossible to define an analytical mode set. If (as is usual), a corrugated matching taper is included at the input and output, then the variety of cross-sections generated compound the problems of analysis. A novel method of modelling is proposed which uses only the modes of a constant-diameter circular waveguide to obtain the full four-port S-parameter matrix for the polariser (two ports per polarisation for the dominant TE₁1 modes)