| Summary: | 碩士 === 國立中正大學 === 電機工程所 === 98 === Multi-band bandpass filters with independent bandwidth control are investigated in this thesis. The filters interleave different types of resonators to generate multiple passbands and numerous transmission zeros for selectivity enhancement.
The first subject is a dual-band bandpass filter, which is formed by interleaving two different types of stepped-impedance resonators (A-SIR and B-SIR). Each type of SIR resonates at each passband. At the first passband, the A-SIR is under resonance while the B-SIR is below resonance, working as the input/output coupling network for A-SIR. On the other hand, at the second passband B-SIR resonates while the A-SIR acts as inter-coupling element between B-SIRs. Consequently a dual-band response is resulted. The experimental results show that the measured insertion losses are less than 1.1 dB at 2.47 GHz and 1.8 dB at 5.2 GHz. The return losses are greater than 19 dB and 27.6 dB at both bands. Four transmission zeros are located at 1.5 GHz, 3.82 GHz, 5.75 GHz and 7.9 GHz, respectively. The fractional bandwidth can be designed to 8.6 % to 13.5 % and 5.2 % to 7.3 % according to the requirement.
The second subject is the further extension of the previous dual-band response to triple-band response by integrating a lumped passband subcircuit into the previous dual-band circuitry. The measured insertion losses are less than 2 dB at 0.68 GHz, 1 dB at 2.25 GHz, and 1.6 dB at 3.5 GHz, respectively. The return losses are greater than 10.2 dB, 12.2 dB and 26.8 dB at each passband. Six transmission zeros are located at 0.38 GHz, 1.45 GHz, 2.66 GHz, 2.91 GHz, 3.19 GHz and 4.45 GHz, respectively, which result in a great stopband and intra-and suppressions.
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