Study On The Structure And Performance Of Planar Microwave Filters For Wireless Communications

With the rapid development of the wireless communication technology, many newcommunication protocols, which are using different frequency bands and working fordifferent purposes, have been proposed. The contradiction between the limit of thefrequency spectrum and the diversity of the communication bands became thebottleneck of the further development of the communication technology. Therefore,high performance microwave filters, which can solve the problem, have attracted muchmore attentions. At the same time, the development of the mobile communicationsystems, especially the development of the portable handsets, have created everincreasing demand for miniaturized wireless communication equipments, andstimulated the development of the planar microwave filters which became the one of themost attractive research areas. The dissertation makes deeply insight into the importantissues concern the design of planar microwave filters, such as the structure of thedual-mode resonators, the realization of the multi-band bandpass filters and rapidoptimization of the filters which has many resonators, and it is summarized as follows.Firstly, based on the comparison with the microstrip dual-mode resonators, noveldual-mode defected ground structure resonator (DDGSR) is developed, and its resonantcharacteristics and the regulation of the variation of the resonant frequencies are deeplyanalyzed. The relations between the external quality factors of the two modes of theDDGSR and the position of the feed lines are systematically analyzed. Bandpass filterswitch have wide stopband with or without capacitive source-load couplings aredesigned. Meander structures are introduced to the DDGSR to reduce the size of theresonator. Based on the DDGSR with meander structures, compact bandpass filter isrealized.Secondly, use the DDGSRs in the multi-band bandpass filter design. Two DDGSRsare used in series or parallel to realize dual-band bandpass filters respectively. Thenested DDGSRs are used to design compact multi-band bandpass filters which have two,three even four passbands. More compact dual-band bandpass filter is realized byintroducing meander structures in the nested DDGSRs. To reduce the size of the filtersfurthurly, a single DDGSR with multi-level meander lines inside is used to realize adual-band bandpass filter.Thirdly, use DDGSR and traditional microstrip structure resonators to constructhybrid type multi-band bandpass filters. Based on transversal filters which have different types of dual-mode resonators placed in parallel, multi-band bandpass filterswhich have two to five passbands are achieved. Using novel coupling schemes, such asinductive or capacitive source-load couplings, compact and high performance dual-bandand tri-band bandpass filters are realized.Fourthly, deeply analysis is performed on the thoughts and particular executionmethods about the aggressive, implicit and tuning space mapping optimization methods.Using these three types of space mapping methods optimize high temperaturesuperconductor filters with same design targets, respectively. Novel hybrid spacemapping optimization method is developed based on the comparison of theconvergences of the results above. Using the novel optimization method, a hightemperature superconductor filter which has20resonators is successfully designed. Andthis design example verifies the validity of this optimization method for optimization ofthe planar microwave filters with complicated structures.