Edge-conditioned vector basis functions for the analysis of corrugated antenna feeds

Corrugated circular waveguides are essential components in modern antenna feeds where a high degree of symmetry in the radiation pattern or a very low crosspolarisation is required. The presence of the periodic corrugations in the circular waveguide is reflected in the field distributions of the modes of the structure through the Floquet condition. A common method of analysis of corrugated circular waveguides starts from an expansion of the electromagnetic fields in a series of space harmonics. The propagation constants of the Floquet modes are then determined from the boundary conditions at the interface between the corrugations and the uniform part of the waveguide. In this paper the propagation constants of the Floquet modes are determined from the classical eigenvalues of a generalized matrix eigenvalue problem instead of a determinantal equation. A new set of edge-conditioned vector basis functions was presented and used to accelerate convergence of the numerical solution. Results obtained from the present work were compared with available data and excellent agreement was documented.