Research On Cross-Coupled Linear Phase Filter

Filter has become an important component in modern communication system.The mainly function of the filter is to acquire the specific frequency band of input signal and filter out other unnecessary frequency bands,its excellent performances,such as out-of-band suppression and insertion loss in passband affect the quality of the whole communication system.With the rapid development of communication technology,the available spectrum resources are increasingly scarce,however,the expectations of filter with high performance are also increasing,not only requires the ability of high-speed transmission of transmission signals,but also the high-quality and large data of transmission,so in the transmission process,the filter not only requires to has good amplitude-frequency characteristics,but also approximately linear phase characteristics,so that the filter can achieve good transmission quality.Therefore,linear phase filters have great research space and important research value.With the development of high integration and miniaturization of communication system,microstrip lines and traditional metal waveguides,which are often used to fabricate filtersare become unsuitable for the application of communication systerm due to their shortcomings.Substrate Integrated Waveguide not only has the characteristics of low insertion loss and high Q value of waveguide,but also has the characteristics of small microstrip size and easy integration.Therefore,Substrate Integrated Waveguide has become one of the research hotspots.Using the new SIW waveguide structure,two transmission zeros are generated at the corresponging stopband frequences by cross-coupling technology,the topological structure of SIW waveguide resonator,the coupling between resonators,the coupling characteristics between resonators and the input and output modes of signals are studied.Fourth-order linear phase filter is realized,which has good out-of-band selectivity,flat group delay and low insertion loss:the center frequency of the filter is f₀=2.5GHz,the relative bandwidth is2.3%,Out-band suppression acheive 40 dB,intraband group delay is 9ns,the flatness up to standard.The research on the structure characteristics of a new type of filter in this design has significant effect on improving the group delay characteristics of the filter and reducing the size of the filter,it has good application value in the fields of microwave,communication and so on.