New Coupling Scheme for Microstrip Bandpass Filters With Quarter-Wavelength Resonators

A new coupling scheme for microstrip bandpass filters with quarter-wavelength (lambda/4) stepped-impedance resonators is proposed. In the proposed coupling scheme, two adjacent lambda/4 stepped-impedance resonators are coupled by directly connecting an admittance inverter between them. By properly d...

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Bibliographic Details
Published in:IEEE transactions on microwave theory and techniques 2008-12, Vol.56 (12), p.2930-2935
Main Authors: KUO, Tsung-Nan, LIN, Shih-Cheng, WANG, Chi-Hsueh, CHUN HSIUNG CHEN
Format: Article
Language:English
Subjects:
Admittance
Applied sciences
Band pass filters
Bandpass filters
Bandwidth
Circuit properties
Couplings
Electric, optical and optoelectronic circuits
Electrical impedance
Electronic circuits
Electronic equipment and fabrication. Passive components, printed wiring boards, connectics
Electronics
Exact sciences and technology
Frequency filters
Inverters
Joining
Joining processes
Magnetic separation
Microstrip bandpass filter
Microstrip filters
Microstrip resonators
Microwave circuits, microwave integrated circuits, microwave transmission lines, submillimeter wave circuits
Microwaves
Oscillators, resonators, synthetizers
quarter-wavelength (\lambda/4) resonator
Resonator filters
Resonators
stepped-impedance resonator
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Summary:A new coupling scheme for microstrip bandpass filters with quarter-wavelength (lambda/4) stepped-impedance resonators is proposed. In the proposed coupling scheme, two adjacent lambda/4 stepped-impedance resonators are coupled by directly connecting an admittance inverter between them. By properly designing the connecting position, one may adjust the coupling coefficient between two resonators so that narrow to broad bandwidth filters may easily be fabricated without coupling gaps. Here, the admittance inverter is realized by a lambda/4 stepped-impedance line. Based on the proposed coupling scheme and the conventional magnetic coupling structure, the filters with narrow or wide bandwidth may be designed and implemented. In addition, folded lines are adopted to make the filter size compact. In this study, a two-pole filter with a 3-dB bandwidth of 5.1% and two four-pole filters with 3-dB bandwidths of 33% and 51% are successfully fabricated. Good agreement between measured and simulated results is observed.
ISSN:0018-9480
1557-9670
DOI:10.1109/TMTT.2008.2007320