Extreme broadband waveguide diplexer design for high performance antenna feed systems

A novel broadband waveguide diplexer design serving two frequency bands with up to 20% bandwidth out of an overall frequency band of more than 65% (3.5 to 7.15GHz) is established. Since the overall extreme frequency demands exceed the operating bands of standard rectangular waveguide types with sole fundamental mode propagation, three different waveguides are considered for the interfacing, namely a dual ridge type at the common port and different standard rectangular ones (WR229, WR137) at the ports serving the assigned frequency bands. A conductor loaded H-plane T-junction is used for the common branching facing at one port the common dual ridge waveguide interface of the diplexer. The other ports of the T-junction are directed to ridge waveguide filter types for the separation of the dedicated wide passbands with up to 20% bandwidth. The opposite ports of these filters are directly adapting to the assigned standard waveguide types for the dedicated served frequency band. It is shown that this approach satisfies high performance properties with a very compact implementation. The overall design has been supported with a full wave CAD method. The measured characteristics exhibit good coincidence with the computed ones and thus validate the broadband design approach. The high performance demands qualify this diplexer design for the implementation in modular feed systems for large radio antennas to provide multi access for serving several frequency bands simultaneously.