Design And Application Of Wide Stopband And High Selectivity Characteristics Of Waveguide Filters

Microwave filters are indispensable components in communication systems,and their performance directly affects the quality of the entire communication system.The rapid development of wireless communication technology not only provides great convenience to people’s lives,but also makes the spectrum resources in communication systems increasingly tense,leading to increasingly serious interference between signals between systems.In order to cope with such a complex system,higher requirements are also put forward for microwave filters,which not only meet the basic filtering function requirements of the receiver,but also require good selectivity and wide stopband characteristics.Waveguide filters have been widely used in communication systems due to their advantages such as high power,low insertion loss,and high stability.In this thesis,the research on the high selectivity and wide stopband characteristics of waveguide filters will be carried out.The research content of this article is summarized as follows:1.Based on the theoretical foundation of microwave filters and rectangular waveguide technology,a fifth order CT cross-coupled waveguide filter with transmission zeros in the upper stop band is designed using an inductive membrane as a coupling structure.Then,based on the analysis of the shortcomings of cross-coupling,a fifth order waveguide filter with symmetric transmission zeros is designed by introducing frequency-dependent coupling into the cross-coupling path.The accuracy of the design method is verified by processing and measuring the designed filter.2.By analyzing the resonant modes in a rectangular waveguide resonator to explain the reasons for the formation of parasitic passbands,and combining the analysis of the operating principle of the capacitance loaded equivalent circuit of the transmission line,a waveguide filter with a wide stopband is designed.This method can push the resonant frequencies of those spurious modes to higher frequencies without affecting the transmission of the fundamental modes in the filter,thereby pushing the parasitic passbands formed by the spurious modes to higher frequencies.The spurious free frequency range of the filter can be extended to 21.2 GHz.At the same time,based on the structure of this wide stopband waveguide filter,a frequency variable coupling element is introduced into the coupling structure,and a transmission zero point is added to the upper stopband,making the filter not only have a wide spurious free frequency range but also have good frequency selectivity.The accuracy of the design method is verified by processing and measuring the designed filter.