Study On Multi-mode Resonators And Their Application To Microwave Filters

With the rapid development of wireless comunication systems, many newtechnologies can be seen everywhere, such as Wlan,3G and4G. The emergence of newtechnoligies makes the design of microwave components quite challenging. Filter is oneof the most basic microwave components, and its indices has become more and morestringent, such as miniarizaiton, low insertion loss, high passband selectivity andwide-stopband. In order to make multiple communication modes operatingsimultaneously, wideband and multi-band filters are the most popular candidates.Dual-mode resonators, which feature compact size, high performance, and low cost,have been widely used in the filter design. According to the study on the publisheddual-mode resonators, this paper proposed many novel dual-and multi-mode resonators,and their resonance and coupling characteristics have been analyzed in detail. In thispaper, these proposed resonators have been employed to design filters.The author’s works are concluded as follows:1. The application background odd-even-mode method has been studied andemployed to analyze the resonance characteristics of four centrally stub-loadedresontors (CLRs). In this way, a novel dual-mode resonator is observed, which is veryimportant to the latter work in this paper.2. For the first time, a novel short-ended dual-mode resonator has been proposed,and its resonance and coupling characteristics have been given detailed analysis throughthe equivalent transmisson line theorem. For wideband application, an improtantparameter, the external coupling, has been analyzed in quantitative, which successfullydescribes the poles within the passband. Moreover, source-load coupling is introduced,which not only enhance the passband selectivity, but also improves the in-band property.In addition, open-circuit stub is loaded to realize filter miniaturization, and it will beused to design dual-mode dual-band bandpsss filters (BPFs), in the design, the externalcouplings of both passbands can be controlled simultaneously, and good impedancematching can be acheived in each passband.3. A novel short-ended stepped-impedance dual-mode resonator is proposed basedon the short-ended dual-mode resonator, and the odd-even-mode method is adopted toanalyze its resonance characteristics, from which, its design graph is given. For the firsttime, a tri-band filter with three passbands whose center frequencies are controllable isimplemented by using only one dual-mode resonator. In bandpass filter design, the firstspurious occurring at4.2f0can be achieved by choosing a reasonable impedance and length ratio. In dual-and tri-band filter design, according to the voltage distributionalong the resonator, three passband external couplings can be controlled, and goodimpedance matching for each passband can be obtained.4. Based on stub-loaded resonators, serval kinds of tri-and quad-mode resonatorsare proposed, and systemically study on their resonance and coupling characteristics iscarried out. The proposed resonators can be used to design bandpass and dual-band filter.A dual-band filter designed by a novel short-circuit stub-loaded quad-mode resonatorfeatures compact size and wide stop-band property. Another dual-band filter based on anovel short-circuit stub-loaded square-loop resonator can exhibit high passbandselectivity and band-to-band isolation. Moreover, novel tri-and quad-mode resonatorsare proposed and employed to design bandpass filters.5. Systemically study on the characteristics of dual-frequency impedancetransformer, which is applied on the transformation of the two inequality impedance tothe standard one. Steeped-impdance resonator (SIR) can be regarded as generalizeddual-mode resonator, and its resonance characteristics are analyzed by theodd-even-mode method. Meanwhile, SIR feeded by stepped-impedance dual-frequencytransformer is functioned as common cavity, which is employed to design diplexers andquadruplexer. During the design, parameters extraction of the simulation model isutilized in the caculating of SIR resonant impedances at two frequencies. In this way,the dual-frequency impedance transformer can be designed more accurate andpractically.