Design Of Compact Multi-band Bandpass Filter Based On Multi-mode Resonator

With the rapid development of wireless communication technology, multiple wirelesscommunication protocols have been proposed and applied. In recent years, to fulfill theincreasing capacity of wireless communication technology, as one of the key components ofRF front-end, the filter is of great interest. With the advantages of high insertion loss, smallscale, flexible modes and high selectivity, multi-mode resonators have gain a lot attentionfrom global researchers. The characteristics of multi-mode resonator provide effectiveapproaches to realize multi-band characteristic, miniaturization and excellent performance.Based on the theoretical analysis of multi-mode resonator, approaches to further decrease thesize of circuit and increase transmission performance are investigated, and multipleconfigurations of compact multi-band BPFs are designed. In addition, high-temperaturesuperconducting (HTS) filter is also analyzed. The compact multi-band BPFs proposed in thisarticle all feature individually adjustable band location and bandwidth.The research in this article can be summarized in following aspects:First, the resonant characteristics of a bent stepped-impedance resonator (SIR) with ashort-circuited stub perturbation are investigated by even-and odd-mode mode analysis. Theinfluence of parameters on the resonant frequency and current distribution is validated withsimulation. Based on this analysis, a miniaturized triple-band BPF using a multimode SIRwith a0°tapped-feed structure is presented.Second, the resonant characteristics of the proposed SIR with a T-shape open-circuitedstub perturbation are investigated. Detailed equations and the relations between resonantfrequencies and important parameters are obtained. To further the analysis, a compacttriple-band high-temperature superconducting microstrip BPF using multimode SIR and afolded uniformed impedance resonator (UIR) is designed.Third, a quad-mode stub-loaded resonator is introduced and investigated. A triple-bandBPF is designed based on the quad-mode resonator. A T-shape open-circuited stub is added tothe quad-mode resonator to realize a compact quintuple-mode resonator, and a triple-bandBPF is designed.The filter circuits discussed above are all manufactured and tested. The simulation andmeasured results match very well. The proposed compact multi-band BPFs with excellentperformance are realized.