Research On Reconfigurable Microwave Filter Based On Evanescent-mode Cavity Resonators

The current era is in the third and fourth scientific and technological revolution,that is,the superposition and transition of electronic information to digital intelligence era.Integration,muti-function,automation and intelligence of microwave circuit and system will provide technical support for digital intelligent era,its research has become the main direction of electronic information technology development.The realization of reconfigurable filter using evanescent mode resonator through electromagnetic coupling technology is of great significance for the integration,multi-function,automation and intelligence of microwave circuits and systems.Therefore,the research topic of this paper is "Research on reconfigurable microwave filter based on evanescent-mode cavity resonator".Reconfigurable multifunction filter is the key component of phased array radar,integrated electronics to realize electronic integration,multi-function,automation and intelligence.As the key components of microwave circuits and systems,such as filters,switches and couplers,they usually exist in the cascade mode in the RF front end of various application scenarios,and have problems such as single function,large volume,large loss or impedance mismatch,which has become the key technology bottleneck of the development of electronic information technology industry.To break through this bottleneck,to realize multifunction and integration,to reduce volume,to reduce cost,to enhance the flexibility and selectivity of transceiver system,is the key to the innovation and development of electronic information technology.The technology of evanescent mode filter can realize large tunable range and provide high Q value resonator,becoming one of the key technologies of reconfigurable multifunctional filter to improve integration performance and electronic automation and intelligence.Therefore,it is very necessary to strengthen this area of research.Thus,this paper proposes a series of multi-functional reconfigurable filter circuit design methods by realizing the fusion of reconfigurable functional and reconfigurable frequency in a single circuit,such as reconfigurable center frequency and the transmission zeros filter based on evanescent mode,reconfigurable filtering coupler based on the evanescent mode cavity resonator,reconfigurable filtering single-pole-multi-throw switch based on evanescent mode cavity resonator,reconfigurable filtering crossover based on evanescent mode cavity resonator and reconfigurable filtering beam-forming network based on evanescent mode cavity resonator.The design method optimizes the overall circuit structure,which can effectively reduce the size and loss of the communication system.The following is a detailed statement of the research content from five aspects:1.Aiming at the problem that the center frequency and transmission zero of the existing trisection filter,where all coupling is mixed coupling,are difficult to be reconfigurable and the position of transmission zero cannot be determined quickly,a reconfigurable filter design method based on evanescent mode resonator is proposed,which can quickly determine the position of transmission zero.By studying the mechanism of evanescent mode resonator and the correspondence relationship between electric coupling and magnetic coupling,the reconfigurable methods of center frequency and transmission zero is given,and the reconfigurable circuit is realized based on evanescent mode resonator and mixed coupling.The experimental results show the center frequency can tune between 2.11 and 2.83 GHz,and the transmission zero can be reconfigurable at any position.The proposed method can be used to quickly determine the transmission zero position.2.Aiming at the problems of low integration and single function of existing reconfigurable couplers,and difficult to adapt to different application scenarios in the future,a functional reconfigurable filter coupler is proposed to solve the problem,which realizes the control of frequency,bandwidth and power ratio of filtering rat-race couplers,filtering-branch line couplers and multi-order filters.By using the odd-even mode analysis method,the coupling coefficients of rat-race couplers,branch-line couplers and multi-order filter are studied,and the functions of filtering rat-race couplers,filtering branch-line couplers and multi-order filter are switched.The experimental results shows that the single circuit can realize the functions of branch-line coupler and rat-race coupler in the 2.08-3 GHz passband adjustment range,and the bandwidth and power ratio can be reconfigurable.At the same time,the second,third and fourth order filter functions are switched by changing the coupling to zero coupling.It solves the problems of low integration,single function and difficult to adapt to different application scenarios in the future.3.Aiming at the problem of low integration of filter and switch and mismatch between stages,a design method of reconfigurable filter switch based on evanescent mode cavity resonator is proposed,which can realize the function of filtering single-pole-multithrow switch.The high isolation and low insertion loss circuit of reconfigurable filtering single-pole-multi-throw switch is realized by studying zero coupling technology.The center frequency tunable range of the filter single-pole-5-throw switch is 1.866-2.257 GHz,the relative bandwidth of 3d B is 4.5%,and the insertion loss varies between 2.45 and 2.13 d B,which realizes the integration with the filter and solves the problem of mismatch between stages.4.Aiming at the problem that the traditional crossover has single function and does not integrate the function of reconfigurable filter,a solution path of multi-function reconfigurable filtering crossover based on evanescent mode cavity resonant is proposed,which can realize the integration function of asynchronous reconfigurable filtering crossover and filtering power divider.By studying the zero-coupling technology to realize the disconnection of adjacent coupling,the asynchronous reconfigurable filtering crossover and filtering power divider can be realized.The test results show that in asynchronous crossover mode,when channel 2 was fixed at 2.8 GHz and the insertion loss was 2.5 d B,channel 1 could be tuned from 1.77 GHz to 2.66 GHz with an insertion loss of 1.68-2.13 d B.When channel 1 is fixed at 1.7 GHz with an insertion loss of 3.07-1.8 dB,channel 2 can be tuned from 1.81 GHz to 2.79 GHz with an insertion loss of 3.58-2.5 d B.In filtering power-divider mode,the center frequency can be tuned from 1.7 GHz to 2.85 GHz with insertion loss of 1.44-2.35 d B.5.Aiming at the problems of low integration,large volume and single function of traditional beamforming network,a reconfigurable filtering beamforming network solution path based on filter switching coupler and twisted broadband coupler is proposed.By studying the theory of coupler,the organic combination of novel filtering switchcoupler,single-pole-double-throw switch,twisted broadband rat-race coupler and crossover is adopted to realize the output phases of 0°,180°,90° and-90°.The test results show the designed beamforming network integrates filtering capabilities without switching ports and achieves arbitrary adjustment of 0°,180°,90° and-90° in the range of 2 GHz-2.2 GHz.It solves the problem that the traditional beamforming network port switch realizes different phase scanning,the fixed working frequency and low frequency selectivity.