Research On Design Technologies Of Multi-band And Balanced Microwave Filtering Circuits Based On Coupled Resonators

In view of the development demands of modern wireless communication and radio sky survey,this thesis carries out a research on high-performance multi-band and balanced microwave filtering circuits with miniaturization,which aiming at the engineering requirements of multi service,anti-interference and miniaturization of RF receiver front-end in complex electromagnetic environments.The article mainly discusses the design techniques and implementation of multi-band filter and filtering antenna,and balanced high-order superconducting filter based on coupled resonators.The main works of this thesis are as follows:1.A kind of low frequency ratio dual-band bandpass filter(BPF)with controllable transmission poles(TPs)and transmission zeros(TZs)is designed based on coupled resonator pairs.The synthesis and design methods of this kind of filter are also given in the paper.By properly arranging the coupling coefficients of the filters,the frequency ratio and bandwidths of the two passbands can be flexibly controlled without changing the resonator sizes.On this basis,three novel dual-band BPFs with different frequency ratios are designed.The filter based on uniform-impedance coupled resonators is realized with a passband frequency ratio of 1.18.The filter based on stepped-impedance coupled resonators is realized with a frequency ratio of 1.30,wide stopband and controllable TZs.The filter based on improved stepped-impedance coupled resonators is realized with a frequency ratio of 1.05,wide stopband,independently controllable passband frequencies and TZs.2.A mixed electric and magnetic(EM)coupled multi-mode stepped-impedance resonator(SIR)is proposed to design a triple-band filter with high isolation.Multiple TZs between the passbands of the filter are generated based on mixed electric and magnetic coupling,which greatly improve the band-to-band isolations.In order to further improve the adjustment freedoms of multiple passbands,a structure of magnetically coupled line-perturbed multimode resonator is proposed to develop a quint-band high-temperature superconducting(HTS)BPF.By properly changing the lengths and position of the magnetically coupled perturbation line in the multimode resonator,both the resonant TPs of odd/even modes and degenerate modes can be controlled,which is beneficial for multi-band design.Source-load coupling,spurlines and shunt stubs loaded on the I/O ports are introduced to generate multi-TZs between the passbands and upper stopband to enhance the band-to-band isolations and out-of-band harmonic suppressions.The designed quint-band BPF is implemented by HTS technology,which effectively reduces the insertion losses of the passbands.3.A balanced electromagnetically-coupled resonator pair based on a newly designed shunted-line SIR is proposed.A compact wide-stopband dual-band balanced BPF is also designed based on the coupled resonator pair.The first two desired passbands can be obtained while keeping the third spurious frequency far away for wide-stopband design,and discriminating differential-mode(DM)and common-mode(CM)harmonics for high CM suppressions by using the proposed shunted-line SIR.Multi-TZs are generated and investigated by means of equivalent circuit model.It reveals that four TZs around the two operating bands can be flexibly controlled via adjusting the ratio of magnetic and electric coupling coefficients of the SIR pair as well as the coupling space of the feeding lines,which have greatly enhanced the passband selectivities and the band-to-band isolation.In addition,the filter owns multiple degrees of design freedom of coupling coefficients and external Q-factors for bandwidths control.A balanced electromagnetically-coupled trisection structure based on the shunted-line SIR is also proposed to design a dual-band balanced BPF with high band-to-band isolation and wide-stopband.Multi-TZs are achieved to realize high passbands isolation and enhanced DM stopband owing to the multi-path coupling and shunt stubs loaded on the I/O ports.4.Three types of balanced SIR pairs with different electric and magnetic coupling characteristics are proposed to design high-order superconducting balanced BPFs and a sixth-order switchable superconducting balanced BPF.The DM phase shifts,CM suppressions and DM&CM coupling coefficients of the three coupled SIR pairs are firstly investigated.Three kinds of high-order Quasi-elliptic filter topologies based on cascaded EM-coupled resonators are also discussed.Then,three kinds of high-order balanced BPFs with Chebyshev/Quasi-elliptic response are designed by using the proposed coupled SIR pairs.Finally,a sixth-order narrow-band balanced BPF with cross-coupling topology and Quasi-elliptic response,and a sixth-order balanced BPF with switchable filtering responses,are developed by using HTS technology,respectively.The magnitude and phase delay of the DM transmission paths are illustrated to explain the TZs production.A pair of symmetric TZs are produced on both sides of the passband,which achieves a Quasi-elliptic response.The designed superconducting balanced filter owns the characteristics of high selectivity,low insertion loss and wide stopband.The switchable superconducting balanced filter can perform either Quasi-elliptic response with steep passband edge or Chebyshev response with flat and deep stopband by elaborately designing the switchable section with reduced loss.5.An efficient filter-antenna integration methodology is investigated based on equivalent circuit model of resonator-antenna coupling.The newly expressed radiation Q-factor of the antenna and coupling coefficient between the antenna and resonator in circuit synthesis are derived.The synthesized parameters are then extracted by an simplified extraction method based on reflection coefficients.Eventually,a planar microstrip dual-band filtering antenna is implemented for example to illustrate the design procedure.The designed filtering antenna owns controllable frequencies and good frequency selectivity,which well improves the out-of-band rejection.