Studies On Hign-performance Microwave Filter Based On Stepped Impedance Resonator

With the emerging of frequency standards, such as Wireless Local Area Network（WLAN） at2.4GHz/5.2-5.8GHz, Global System for Mobile Communications （GSM） at900MHz/1800MHz and other frequency standards, the interference between differentcommunication systems have turned into a prominent issue. For the sake of reducing theinterference, the selectivity and isolation of the RF front-end of receiver need to be improved.As a key component in the RF front-end, microwave filters determine the characteristic of thewireless system. The research on high-performance filter with good selectivity and lowspurious passband has important theoretical value and broad application prospects.First of all, two bandpass filters with wide-stopband are presented in this thesis. Thefilter is realized by using stub-loaded stepped-impedance resonator （SIR）. SIR and the loadedstub can produce two resonant frequencies in the passband. One BPF is realized by using astepped impedance stub loaded SIR, and its stopband frequency range is extends to3f₀. Theother circuit is constructed by asymmetrical loading. Two transmission zeros have beenachieved at the edge of the passband and good selectivity has been obtained. Wide stopbandfrom2.5GHz to6.5GHz with insertion loss below-20dB has been acquired in the filter.Secondly, a dual-band and a triple-band BPF are proposed based on stub-loadeddual-mode resonators. The dual-band filter with central frequencies of2.4GHz and3.5GHz isconstructed by a uniform impedance stub loaded resonator and a stepped impedance stubloaded resonator. The central frequencies and bandwidths of each passband can be controlledseperately. Based on the above principle, a dual-mode triple-band bandpass filter is designed.Designing theory is verified by the measured results.Finally, triple-band BPFs are realized by using a pair of SIRs. A two-pole triple-bandBPF is designed using two coupled SIRs. Triple passbands are realized by using thefundamental resonant, second and third harmonic of the SIR. The other triple-band BPF isformed by using shorted-stub-loaded SIR. Even-and-odd mode theory is applied to analysisthe shorted-stub-loaded SIR. Two odd-modes and one even-mode are used in the filter. Atriple-passband BPF with central frequencies of1.5GHz for GPS and2.4/5.8GHz for WLANis designed. The proposed filters are very compact because they are realized only using twocoupled resonators.