| Summary: | 碩士 === 國立彰化師範大學 === 電子工程學系 === 95 === In this thesis, multi-band microwave bandpass filters (BPFs) designed using cross-coupled stepped-impedance resonators (SIRs) were studied. Three microwave filters, including two dual-band and one tri-band BPFs were designed, implemented, and investigated. The first dual-band BPF circuit consists of a pair of L-shape half-wavelength ( ) stepped-impedance resonators (SIRs) and an inverted Z-shape resonator. The latter is actually a combined structure of two SIRs so designed to provide a magnetic coupling path and to reduce the circuit size. Cross-coupled SIR configuration and tapped-feed structures are adopted to introduce attenuation poles around the passband edges for selectivity improvement. A wider -20-dB upper stopband is achieved by properly separating the third resonant frequencies of the SIRs of different types. The second BPF proposed in this thesis was a compact fourth-order dual-band BPF having a wide upper-end stopband. Quarter-wavelength ( ) SIRs were employed to construct the BPF in order to have a relatively smaller circuit size and higher spurious passband, as compared with the BPF using SIRs. The resonators tapped by the input and output ports were loaded by a spur-line to suppress the first spurious passband so as to further broaden the upper-end stopband. BPFs with and without the embedded spur-lines were both simulated for comparison of their frequency responses.
Finally, we presented in this thesis a second-order tri-band bandpass filter (BPF) designed using tri-section SIRs (TSSIRs). The impedance ratios of the TSSIRs were computed using the formula expressed as functions of the passband center frequencies, which are commercially practical and located at 1.57, 2.45, and 3.5 GHz. A cross-coupled configuration was arranged to sharpen the passband skirts. The newly designed tri-band BPF was verified by circuit implementation and very good agreement between the simulated and measured results was observed.
Results obtained in this research can be applied to commercially practical RF and microwave systems. The techniques presented in this research are expected to serve as a useful reference for microwave filter designers in this and related research fields.
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