Researches On Microstrip Ultra-wideband Bandpass Filters

With the rapid development of communication industry, ultra-wideband (UWB) wirelesscommunication technology has attracted a wide attention in the world with the advantages ofsimple structure, low cost, low power consumption, high speed rate, high security. As one ofthe key passive components in the UWB system, the UWB bandpass filter has a significantimpact on the performance of the whole system. This dissertation gives a detail study on thedesign technique of compact planar UWB bandpass filters. Novel resonators with goodcharacteristics and modified coupling structures are presented, and different UWB bandpassfilters with high performance are designed by adopting the proposed structures. The maincontributions of the dissertation can be summarized as follows.1. Based on the stub-loaded resonator, a novel stepped-impedance stub-loaded resonator(SISLR) is proposed in this dissertation. Resonant characteristics and transmission zeros ofthe proposed triple-mode and quintuple-mode SISLRs are analyzed in detailed viatransmission line theory. The proposed SISLRs can not only provide more degrees of freedomto adjust the resonant frequencies, but also generate two transmission zeros near the cut-offfrequencies of the UWB passband, which will contribute to high skirt selectivity of the UWBbandpass filter. High performance UWB bandpass filters are presented using the proposedtriple-mode and quintuple-mode SISLR, respectively.2. In order to improve the upper-stopband performance of the UWB bandpass filters,two design methods are presented form the point of view of multiple-mode resonator andcoupling structure, respectively, one of which is realized by constructing aharmonic-suppressed multiple-stub loaded resonator, while the other by modifying theconventional parallel-coupled lines with loaded folded stubs. Two kinds of UWB bandpassfilters with high selectivity and improved upper-stopband performance are design by adoptingthe modified multiple-stub loaded resonator and coupling structure, respectively.3. Based on the cross-shaped resonator, a novel fish-bone resonator is presented andanalyzed in this dissertation by cascading multiple cross-shaped resonators. Meanwhile, anovel coupling structure is study in connection with the special configuration of the fish-boneresonator. Two kinds of wideband bandpass filters with high performance are constructed by two stages and four stages fish-bone resonators, respectively. In order to achieve highselectivity, a fish-bone resonator with loaded stepped-impedance stub is presented for thedesign of the UWB bandpass filter.4. In view of the necessity of notch band characteristics to UWB bandpass filters, anovel notched structure with simple structure, controllable notched frequencies andbandwidth is presented in this dissertation. Two kinds of UWB bandpass filters with singleand double notched bands characteristic are constructed by embedded the notched structuresto the basic UWB bandpass filter. The proposed filters are fabricated and measured. Themeasured and simulated results are in good agreement with each other.