Research And Design Of RF Tunable Filter Based On Reconfigurable Coupling Matrix

RF filter is an essential passive component in wireless communication system.With the development of reconfigurable wireless communication system in the future,the research on tunable filter and its miniaturization has attracted more and more attention.However,at present,the research of tunable filter is only limited to the filter design level,lack of theoretical guidance,which greatly limits the further development of tunable filter.Based on the synthesis method of traditional fixed filter,a new reconfigurable coupling matrix is proposed in this paper.By studying the circuit network of low-pass prototype,the reconfigurable coupling matrix based on Butterworth low-pass prototype and Chebyshev low-pass prototype is designed.The reconfigurable coupling matrix contains the variable elements of bandwidth,which is suitable for the design of any order tunable bandpass filter.On the basis of the reconfigurable coupling matrix,the mapping relationship between the reconfigurable coupling coefficient and the tunable components is studied.By finding the intermediate variable relationship,the coupling matrix containing variable elements is connected with the physically realizable varactor diode,thus the design of the tunable filter can be realized.In order to obtain a more compact structure,the method of miniaturization of the resonator is studied in this paper.A compact resonator structure(CRLH-QMSIW)is proposed by using the composite right/left-handed transmission line(CRLH TL)and a quarter-mode mode substrate integrated waveguide(QMSIW)resonator.A second-order compact bandpass filter with high out of band rejection is designed.The filter has a small volume and good passband performance on the premise.what's more,three transmission zero points(TZs)are introduced to improve the out-of-band rejection of the passband.Based on the theory of reconfigurable coupling matrix and miniaturized resonator proposed in this paper,two fully tunable bandpass filters of second-order and fourth-order are designed by using Butterworth low-pass prototype and Chebyshev low-pass prototype.These two kinds of tunable bandpass filters are designed and fabricated,the simulation and test results show good agreement,which also proves the correctness of the reconfigurable coupling matrix theory proposed in this paper.In this paper,the theoretical synthesis process of the reconfigurable coupling matrix is proposed for the first time,and the coupling matrix is directly associated with the tunable device,which provides theoretical guidance and basis for the design of the reconfigurable filter.This method has important research significance for tunable filters.