Varactor-tuned combline bandpass filter using step-impedance microstrip lines

In this paper, a varactor-tuned combline bandpass filter using step-impedance microstrip lines is considered so that the absolute passband bandwidth can be maintained nearly constant within the tuning range. The difference between the odd- and even-mode characteristics of the coupled microstrip line...

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Bibliographic Details
Published in:IEEE transactions on microwave theory and techniques 2004-04, Vol.52 (4), p.1279-1283
Main Authors: Kim, B.-W., Yun, S.-W.
Format: Article
Language:English
Subjects:
Band pass filters
Bandwidth
Couplings
Frequency
Inductors
Magnetic separation
Microstrip filters
Passband
Resonator filters
Tuning
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Summary:In this paper, a varactor-tuned combline bandpass filter using step-impedance microstrip lines is considered so that the absolute passband bandwidth can be maintained nearly constant within the tuning range. The difference between the odd- and even-mode characteristics of the coupled microstrip line makes it difficult to design a tunable bandpass filter with minimum degradation in passband performance. By using step-impedance microstrip lines, couplings between resonators can be controlled so that the constant bandwidth requirement could be satisfied with reasonable design parameter values. Lumped inductors are used for input and output coupling networks. Design equations are derived, and experimental results are compared with theoretical ones based on these equations.
ISSN:0018-9480
1557-9670
DOI:10.1109/TMTT.2004.825626