Cutoff and bandwidth characteristics of a circular coaxial waveguide with four symmetrically placed double ridges

A dielectric-cone-loaded, hybrid-mode feed horn was developed for broadband applications (Clark and James 1995). Using the mode-matching method, that analysis showed that the bandwidth of this feed horn is extremely broad, and it can be excited by using a coaxial waveguide for dual-band applications. However, the limited bandwidth of the exciting coaxial waveguide inhibits the full potential of the horn to be realised. In order to couple the incoming/outgoing waves from the wideband horn without sacrificing its broad dual-band capability, we propose a coaxial waveguide with four symmetrically placed double ridges. The cutoff and bandwidth characteristics of the proposed structure are analysed using the modified Ritz-Galerkin method, and the results are compared with those obtained using the finite-element method.