Research On Isomorphic Tunable Design Of Miniaturized Planar Dual-Mode Microwave Filters

With the rapid development of modern wireless communication technology, the wireless communication systems which have different working frequencies are increasing gradually, and the new requirements such as miniaturization, multiband applications have being proposed for these systems. Microwave filter acts as a critical component of the front end of wireless communication system and its design technology has also received some new challenges accordingly. Compared with traditional single-mode filter, dual-mode filter has not only the better performance parameters and passband flatness, but also the advantages of miniaturization, therefore has received more attention. The design of the traditional dual-mode filter technique is specific for the working frequency band, if the required working frequencies are changed, it has to be redesigned to meet the new situation. Thus it will cause the extra burden on the time and energy of the research personnel and also impacts on the resource utilization and time schedule of the projects. Therefore, the design of the miniaturization, high performance dual-mode filters which have universal structure, adjustable working frequency bands becomes a new challenging work.The isomorphic tunable design of high performance and compact dual-mode microwave filters used in wireless communication systems has been proposed in this dissertation. Several isomorphic tunable schemes for the design of dual-mode microwave filters are presented. Based on these schemes, some dual-mode wideband bandpass, dual-wideband bandpass and dual-mode dual-band bandpass filters with good performance and compact size have been designed. These filters have the characteristics of low insertion loss, better return loss, high stopband rejection, and compact size etc. These research results have important values for the practical applications and they should be attractive for the design of miniaturized planar dual-mode microwave filters. The main work of this dissertation is summarized as follows:Firstly, various new technologies for the planar microwave filters have been systematically summarized and reviewed. Then, the developmental venations of dual-mode resonators have been expounded. Finally, the design methods for the dual-band bandpass filter and dual-mode dual-band bandpass filter have been analyzed and summarized, and the main research content and direction of this dissertation have been proposed.Secondly, the fundamental theory of stepped-impedance resonator (SIR) and dual-mode resonators related to the research content of this dissertation have been introduced. First of all, the evolutions from uniform impedance resonator (UIR) to SIR are investigated. Then the resonance conditions and odd-even mode equivalent circuit model of center-stub-loaded uniform impedance resonator (CSLUIR) are investigated. Finally, the resonance conditions and odd-even mode equivalent circuit model of center-stub-loaded stepped-impedance resonator (CSLSIR) are investigated.Thirdly, an isomorphic tunable design scheme of planar dual-mode microwave filters based on a CSLSIR and a cross-coupling structure between the input and output feed lines has been achieved. Two dual-mode wideband bandpass filters which may be used to Lower-and Upper-UWB applications and a dual-wideband bandpass filter which has improved upper stopband performance are designed based on this isomorphic tunable design scheme. These planar dual-mode microwave filters based on this isomorphic tunable design scheme have the advantages of high performance, smaller size, simple manufacturing process, and easy integration etc.Fourthly, an isomorphic tunable design scheme of planar dual-mode dual-band bandpass filters based on pseudo-interdigital coupling CSLSIRs and asymmetric direct feed lines is achieved. Then a dual-mode dual-band bandpass filter which may be used in worldwide interoperability for microwave access (WiMAX) and wireless local area network (WLAN) dual-frequencies wireless communication system has been designed based on this isomorphic tunable design scheme. Finally, a dual-mode dual-band bandpass filter which may be used in downlink of C-band and X-band satellite communication systems is designed based on this isomorphic tunable design scheme. These planar dual-mode dual-band bandpass filters which based on this isomorphic tunable design scheme have the advantages of smaller size, low insertion losses, and better return losses, and easy integration for their simple structure etc.Fifthly, an isomorphic tunable design scheme of planar dual-mode dual-band bandpass filters based on complementary coupling CSLSIRs and asymmetric tapped-coupled feed lines is completed. Then a dual-mode dual-band bandpass filter which may be used in worldwide interoperability for microwave access (WiMAX) and wireless local area network (WLAN) dual-frequencies wireless communication system is designed based on this isomorphic tunable design scheme. Finally, a dual-mode dual-band bandpass filter which may be used in WLAN dual-frequencies wireless communication system is designed based on this isomorphic tunable design scheme. These planar dual-mode dual-band bandpass filters based on this improved isomorphic tunable design scheme also have the advantages of smaller size, superior passbands performance, and easy integration for their simple structure etc. Furthermore, this improved design scheme has the advantage of the wide adjustable range of filter operating frequency.In the last part of the dissertation, the research work of this dissertation is summarized, and the potential research directions are predicted.