Research On The HTS Multi-band Filters Basedon Multi-mode Resonators

Bandpass filters(BPSs),utilized to suppress out-of-band jamming signals,are critical components in determining the anti-interference capacity and sensitivity of wireless communication and detection system.With the rapid development of modern communication technology,communication devices will tend to be multi-frequency technology,scale integration and compact size,and an urgent need has witnessed a great increase for multi-passband filters.Fortunately,filters based on multi-mode resonators(MMRs)have more compact circuit size,lower loss and noise.However,restricted by normal metal material and design methods,multi-passband filters based on MMRs suffer lower order and higher in-band insertion loss.Since high temperature superconducting(HTS)film has much lower surface resistance for microwave applications,multi-passband filters fabricated by HTS film have much higher performances than those fabricated by normal metals for lower insertion loss,steeper skirt slope and higher restraint outside the band.Thus,with multi-passband engineering applications,and the advantages of superconducting filter and MMRs,HTS multi-passband filters have played a significant role in academic research and engineering application.The thesis proposes several methods to solve the problems in design of multi-passband filters based on MMRs:(1)A novel method to extract the external quality factor Qe based on the group delay of S21 is proposed,which overcomes extraction difficulties in external quality factor Qe by the traditional method.Besides,an optimized design method is put forward to derive the desired initial resonant frequency and structure parameters of the proposed quint-mode resonator,which successfully improves efficiency of filter design.Finally,based on novel quint-mode resonators,the dual-band BPFs with excellent performance,have been developed to demonstrate the theoretical predictions.(2)The novel embedded stub-loaded resonators(ESLRs)and the capacitively loaded parallel coupled lines are presented to achieve the desired equal coupling coefficients for tri-mode resonator at three resonant frequencies.Because tapped-line structure has more stable fabrication and lower in-band insertion loss,the dual-feed external coupling structure with two feed lines tapped to the resonator is proposed.Finally,based on ESLRs,the tri-band BPF with excellent performance and compact size,has been developed to demonstrate the theoretical predictions.(3)A novel quad-mode sub-loaded resonator,which can separate the electric coupling path and magnetic coupling path between different resonant frequencies,is introduced.Obviously,the coupling coefficients between the resonators at four resonant modes can be adjusted independently.The quad-feed external coupling structure with two coupled lines and two tapped lines provides us with the enough design freedoms in achieving the desired Qe in all the four passbands.Finally,the quad-band BPFs with excellent performance and compact size have been developed to demonstrate the theoretical predictions.It resolves design difficulties in quad-band BPFs based on quad-mode resonators by controlling the passband bandwidths separately.