Multi-mode Filter Design

In this thesis, the theory of designing dual-mode waveguide filters is both proposed and verified. The three main characteristics of this kind of dual-mode filters are presented as followed: First of all, its resonators are rectangular cavities and easily fabricated in production. Secondly, there is no need of adding coupling screws into the overall design; instead, the coupling of two existed modes in the same resonator is realized by changing the dimension of rectangular cavities. Thirdly, evanescent mode waveguide is used instead of cross coupling iris to achieve the coupling of the modes in adjacent cavities.In this thesis, two sample dual-mode filters are designed and fabricated, respectively centered at 9750MHzHz and 6583MHz. The tested result shows a perfect performance of high frequency selection and low insertion loss. Furthermore, a compact capacitance-loaded dual mode filter centered at 6583MHz is achieved based on the capacitance-loaded technology, whose overall size is decreased by 78 percent compared with conventional dual mode filter.The transmission zeros in dual-mode resonator can be easily realized at lower or higher frequency side of pass band. To verify this theory, we designed three point to point communication dual mode diplexers respectively centered at 8GHz, 13GHz and 15GHz. Then a novel configuration of 8GHz point to point communication dual mode diplexer is proposed by using the folded waveguide technology. However, the 50% length reduction is at the cost of hard fabricating and debugging. In order to overcome this disadvantage, in the following we improve 13GHz point to point communication dual mode diplexer by introducing multilayer folded waveguide technology, which achieves better performance in both overall size and debugging.Also, a capacitance-loaded dual-mode waveguide filter is designed and fabricated which gains an over 50% length reduction compared to the conventional direct coupling dual-mode diplexer.