Research And Design Of Microwave Multimode Filter

With the rapid development of communication systems,higher and higher requirements are put forward for the design of microwave filters.Not only are various design indicators more stringent,but the miniaturization design of microwave filters is also receiving the attention of researchers.Considering various ways to reduce the size of the filter,multi-mode resonator technology is undoubtedly one of the most effective and commonly used techniques.Although the research on multi-mode filter of microstrip structure is relatively mature,there are many defects in planar structure filter.And the waveguide cavity resonator has become a good choice for realizing multi-mode resonator because of its advantages such as low insertion loss,high Q value and high power capacity.The design of multi-mode filter based on cavity resonator is a hotspot and important research direction in recent years.This paper focuses on the design of microwave multi-mode filters using cavity resonators.In the past few decades,the multi-mode filter design method has been continuously improved and improved with the development of filter synthesis theory and coupling theory.Now there is a mature design method based on coupling matrix.At the same time,the coupling structure in the cavity filter has been enriched with the research of designers.We can choose the appropriate physical structure according to the design requirements.The main contents of this paper are as follows: Firstly,the basic theory of microwave filter and the basic flow of filter design are introduced.Secondly,the design theory of the waveguide cavity multi-mode filter is introduced in detail,and the miniaturization realization methods of the waveguide resonator are analyzed.At the same time,based on the coupling theory,the intracavity coupling,inter-cavity coupling and input/output coupling of the rectangular waveguide resonator are analyzed and discussed in detail,which is the theoretical basis for the design of the cavity multi-mode filter.Furthermore,the design flow of the multi-mode filter based on the generalized coupling matrix method is given in detail by designing a series topology fourth-order dual-mode waveguide filter.Then,the advantages of the parallel multi-mode filter in generating the transmission zero point are introduced.Based on this,a single-cavity dual-mode filter and two dual-cavity dual-mode bandpass filters with different inter-cavity coupling structures are designed.Finally,this paper designs a sixth-order triple-mode filter based on rectangular waveguide resonators.The L-shaped probe can simultaneously excite three degenerate modes,and the independent coupling of each mode coupling is realized by the hybrid coupling method of the cross window and the electric probe combination.The structure is compact and has good filtering characteristics.The rationality of the design is verified by processing a prototype object.