Theoretical Research On The Planar Microwave Filter In Box-section Coupling Topology And Its Application

Microwave filter is the core device of communication systems,whose performance has an important impact.Filters with the performance of miniaturization,high selectivity,controllable zeros' locations and low cost are research hotspots,among which planar filter in box-section coupling topology(BSCT)is an important research interest.In this paper,BSCTs with diagonal coupling(N?4)and the theoretical analysis method are proposed.And four analysis methods of planar microwave filter in BSCT with diagonal coupling(BSCTDC)are proposed based on single mode(SM),combination of single and dual modes(CSDMs),dual-layer dual modes(DLDMs)and triple mode(TM)with capacitive loading resonators,respectively.The optimization design,planar circuit processing and fabrication,testing and debugging of the above four kinds of filters have been completed,which has verified the accuracy of the coupling topology,analysis method and the design of the four class of box-section filter proposed in this paper.Thus,the theoretical analysis method and application ability of planar microwave filter in BSCTDC based on substrate integrated waveguide(SIW)and microstrip are established.As a result,the key technical problems of microwave filter,such as miniaturization,high selectivity,controllable zeros' locations and low cost,are tackled.The main study contents and innovation work are as follows:1.The BSCTDC(N?4)and its theoretical analysis method are proposed.Based on the zeropole optimization method of characteristic polynomial function,the synthesis method of N+2 order linear frequency-dependent coupling(FDC)matrix is given.The analysis method of mixed electric and magnetic coupling(MEMC)is studied;then,the formula of location of finite transmission zero(FTZ)is modified.The FDC analysis method based on microstrip and SIW is studied,and an FDC structure with realization of positive and negative slope is proposed for the first time.The characteristics of bypass coupling(BPC)are analyzed,and a method to extract the equivalent coupling coefficient of BPC in dual-mode resonator is proposed.On the basis of planar microwave filters in BSCTDC(N?3),the BSCTDC(N?4)and corresponding theoretical analysis method are proposed,which have formed the analytical method and theoretical system of planar microwave filters in BSCTDC.2.Analysis method of BSCT planar microwave filter with diagonal coupling based on SM resonators is proposed.Relationships among the first nine resonances with different aspect ratios in SIW cavity are studied,and 4th-order BSCT single-mode SIW filters based on bypass/magnetic/FDC providing its diagonal coupling and corresponding analysis method are proposed.Characteristic of right-angled isosceles triangular patch resonator is researched;4thorder SM microstrip filters in BSCTDC and corresponding analysis method are proposed.3.Analysis method of BSCT planar microwave filter with diagonal coupling based on CSDM resonators is proposed.Equivalent coupling topologies of filters using a single dual-mode resonator,the CSDM resonators are studied.The characteristic of dual-mode square SIW cavity is analyzed;4th-and 5th-order SIW filters in BSCTDC based on the combination of two single-mode and one dual-mode cavities as well as corresponding analysis method are proposed;4th-order SIW filter in BSCTDC based on the combination of magnetic and bypass couplings providing its diagonal coupling path as well as corresponding analysis method is proposed.The characteristics of the microstrip square ring resonator are analyzed,a new feeding method and structure are proposed to design dual-mode filters;3th-,4th-and 5th-order microstrip filters in BSCTDC based on the combination of multiple single-mode resonators and a single dual-mode resonator as well as corresponding analysis method are proposed.4.Analysis method of dual-extended BSCTDC planar microwave filter based on DLDM resonators is proposed.Equivalent topologies of a filter using two cascaded dual-mode resonators and the equivalent relationship in-between as well as input and output feeding method are studied;4th-order dual-extended BSCTDC and a new feeding method are proposed.The dual-extended BSCTDC SIW filter and corresponding analysis method are proposed.The characteristics of dualmode square ring resonator loaded by capacitive branches are analyzed;then,unbalanced/balanced DLDM square ring filters with realizations of single-and dual-band responses as well corresponding analysis methods are proposed.5.Analysis method of BSCT planar microwave filter with diagonal coupling based on TM resonator with capacitive patch loading(CPL)is proposed.Characteristics of CPL square,circular SIW and microstrip patch resonators are studied respectively;then,six new TM planar resonators with controllable resonances and corresponding analysis method are proposed.Technical problems of triple-mode SIW and patch filters with realization of a quasi-elliptic response are tackled.The proposed techniques based on SM,CSDMs,DLDMs and TM with capacitive loading resonators achieves miniaturized filters.The proposed BSCTDC(N?4)increases the number of FTZs,and thus realizes high selectivity.The filter based on the proposed BSCTDC realizes controllable zero' locations.Single-and double-layer physical topology with high degree of freedom achieves low cost.The effectiveness of the BSCTDC,filters and analysis methods proposed in this paper is verified by simulations and experiments.