The Design Of Dual-mode Rectangular Waveguide Diplexer Using Ridge Resonators

Because of the advantages of characteristics of low loss and high power handlingcapability, waveguide filters are still widely used in satellite applications and aircraftcommunication. But one of the main drawbacks of waveguide structures is their sizeand weight. The use of dual-of multi-mode filters exploiting multiple resonant modeswithin a single cavity is a typical solution to alleviate such problems. This paperintroduces the generalized Chebyshev filter synthesis theory, as well as the fieldstructure and transfer characteristic of guided mode in rectangular waveguide, finally aridge resonators structure has been proposed in this paper. As this ridge resonator doesnot require the enlargement of one cavity dimension or more to produce orthogonalquasi-transverse electromagnetic mode (TEM) degeneracy in rectangular waveguide,thus dual-mode filter can be realized by properly combining this ridge resonators withincompact rectangular waveguide sections.Firstly, the generalized Chebyshev filter matrix synthesis theory and the couplingmatrix theory used matrix rotation to obtain the required CT,CQ topology has beenintroduced. it is a theoretical basis for this design of diplexer. This paper also makes asimple analysis on the guided mode in rectangular waveguide, including the fieldstructure and transfer characteristics of the guided mode, and also shows the fieldschematic diagram of the common modes.Secondly，this paper demonstrates the ridge resonator’s characteristics of fields andshows the simulated results of ridge resonator depending on the way in which itsresonant modes are excited. This paper also analyses the method of controlling the inputand output coupling, as well as the coupling between degeneracy modes. Finally wedesign a two-cavity and four-order dual-mode band pass filter and a six-orderdual-mode and dua-band pass filter based on this theory.At last, a simple-dual mixed waveguide diplexer is designed according to therequirement. The detail procedures of each band pass filter and T-junction are shown inthis paper and test the characteristic of the measured model. Compared with the sameorders single mode waveguide filter, this design of filter has better characteristics and smaller dimensions.