Researches On Multi-mode Bandpass Filters

With the development of data communication and multimedia services, especially the urgent demand of the multi-standard and high quality communication, the design of microwave components are facing new opportunities and challenges. Filters, as the key components of the wireless RF front end, are tendency to the research hotspot of miniaturization, high performance, multi-mode and multi-band. With the advantages of high insertion loss, small size and good stopband performance, multi-mode resonators have gain a lot attention from global researchers. The characteristics of multi-mode resonator provide effective methodes to realize multi-band characteristic, wide-band characteristic, and miniaturization performance for bandpass filter design. This dissertation gives a detail study on the design technique of bandpass filters using multi-mode resonators, some resonators with easily controlled resonance frequencies and coupling structure are presented, and different multi-mode narrow-band, multi-mode wide-band and multi-mode multi-band bandpass filters and diplexers of good performance are designed using these resonators. The main contributions of the dissertation can be summarized as follows.(I) Based on the traditional dual-mode square-loop resonator, the assembled square-loop resonators are analyzed in detail. The proposed filter is realized by coupling a resonator inside without increasing circuit size. Transmission zeros and poles are achieved by coupled resonator. High performance triple-mode, quad-mode and dual-band filters using assembled square-loop resonators are presented in this dissertation.(II)According to the stub-loaded λ/4 resonators, appoaches to realize multi-band bandpass filters using the proposed resonators are researched. Loading point, size of stub, charge/ current distributions and resonance properties of the proposed resonators are analyzed in detail. The first resonance frequency is obtained by tuning of the stubs length of the quarter-wavelength resonators, while the second resonance frequency is unaffected. High performance dualband and quad-band bandpass filters using stub-loaded λ/4 resonators are presented in this dissertation.(III) Based on the stub-loaded centrally half-wavelength resonators, appoaches to realize wide-band bandpass filters using stub-loaded half-wavelength resonators are researched: double-T-shaped stub loaded triple-mode resonator and self-coupled stub-loaded quad-mode resonator. For double-T stub-loaded triple-mode resonator, the first four resonance properties and charge/current distributions are analyzed in detail. Compact triple-mode filter using double-T stub-loaded resonator with high selectivy is presented. Self-coupled stub-loaded quad-mode resonator is investigated by even- and odd-mode mode analysis. Compact quad-mode filter using self-coupled stub-loaded resonator is presented in this dissertation.(IV) In view of dielectric-loaded cylindrical cavities resonator, it is found that two degenerate modes in the same cavity are properly perturbed by an off-centered dielectric resonator(DR) instead of a traditional corner perturbation. It is an effective method with easy design and processing difficulty. It is realizable to build the dielectric-loaded multi-mode filters and diplexers using the proposed resonators.(V) According to helical resonator with two-section of non-uniform pitch angle, it is found that the first two resonance modes can be controlled by pitch angle, so as to achieve controllable frequencies of dual-band filter. In addition, a dual-band helical filter with controllable frequencies and bandwith is achieved by approaching a novel feeding structure and coupling structure. The main advantages of the filter are: small size, high power capacity, controllable bandwidth.