Study On Key Techniques Of Novel Microwave Filters

Modern wireless communication systems, such as satellites and mobilecommunication systems, demand high-performance channel and compact circuit. Thus,a variety of compact and high performance microwave devices are urgently need. Filtersare very important devices in the microwave communication system, and their size andperformance directly impact on the performance of the whole communication system.Based on the actual project requirements, new technologies and new structures aredeeply studied to achieve high selectivity and compact size in this dissertation. Themain contents of this dissertation are listed as follows:Firstly, a detailed research is given on stub-loaded dual-mode filter. The basicprinciples of the open stub and shorted stub loaded dual-mode resonators are described.The dual-mode filters with capacitive and inductive source-load coupling (S-L coupling)based the stub-loaded dual-mode resonator are studied. The generation mechanism ofinherent transmission zero and extra transmission zero is described in detail. A novelultra-compact shorted-stubloaded dual-mode filter is proposed, in which capacitive S-Lcoupling and SIR are utilized. The filter has a compact size, high selectivity and goodharmonic suppression characteristics. The shorted-stub loaded dual-mode filter withinductive S-L coupling is proposed for the first time, which makes the stub-loadeddual-mode filter with S-L coupling perfect. Then, the hexagonal S-L couplingstub-loaded filters are taken as an example to sum up all frequency responsecharacteristics of the stub-loaded dual-mode filter with S-L coupling. Finally, the novelstub-loaded dual-mode filter is studied. The coupling between input/output line andeven mode of novel filter is more stronger than that of between input/output line andodd mode. The all frequency response characteristics of this type of stub-loadeddual-mode filters are predicted in theory.Secondly, the transversal microstrip filter is studied. The basic principle oftransversal filter is introduced. It is pointed out that stub-loaded dual-mode filter in thethird chapter is a type of special second-order transversal filter. The third-ordertransversal filters in the previous reference are summarized. Then, how to design the third-order transverse filter based on stub-loaded resonator is explained. Two compactfull canonical third-order transverse microstrip filter structures are proposed, both ofthem are based on the shorted-stub loaded dual-mode resonator and even-moderesonator. The shorted-stub loaded dual-mode resonator is used in third-order transversemicrostrip filter for the first time. The second transverse filter has good harmonicsuppression.Thirdly, triple-mode filter is introduced. The triple-mode filters in the previousreference are summarized. Then a novel capacitive S-L coupling triple-mode filter basedon the stub loaded in the centre of square loop triple-mode resonator is proposed. Thisfilter has a small size, wide bandwidth and presents three transmission zeros in thestopband.Fourthly, multi-band dual-mode microstrip filter is introduced. The basic theoryand the design methods of multi-band bandpass filter are illustrated, and the multi-bandfilters in the previous reference are summarized. Then the structures of dual-modedual-band filters are introducted. Finally, the compact dual-band and tri-band dual-modefilters are proposed based on short stub and open stub loaded dual-mode resonators.There are no coupling between each mode and each resonator, so the filter designprocess is simplified. The proposed multi-band filter presents full canonical frequencyresponse because of the introduction of S-L coupling. This type of multi-band filterspresent small size, high selectivity and good separation between each band and so on.Finally, a summary of the whole dissertation is given, and future research topicsare suggested.