Varactor-Tuned Dual-Mode Bandpass Filters

• Published in: IEEE transactions on microwave theory and techniques Vol. 58; no. 8; pp. 2213 - 2219
• Main Authors: Tang, Wenxing, Hong, Jia-Sheng
• Format: Journal Article
• Language: English
• Published: New York, NY IEEE 01.08.2010; Institute of Electrical and Electronics Engineers; The Institute of Electrical and Electronics Engineers, Inc. (IEEE)
• Subjects: Applied sciences; Band pass filters; Bandpass filters; Bandwidth; Circuit properties; Circuits; Coupling circuits; Dual-mode resonator filter; Electric, optical and optoelectronic circuits; Electronic circuits; Electronics; Exact sciences and technology; Frequency; Frequency filters; Joining; Mathematical analysis; Microstrip filters; Microstrip resonators; Microwave circuits, microwave integrated circuits, microwave transmission lines, submillimeter wave circuits; Microwave filters; Microwaves; Oscillators, resonators, synthetizers; Resonator filters; Resonators; Tunable circuits and devices; tunable filter; Tuning; Microstrip filters; Resonator filters; Operating mode; Microstrip resonator; Tuning; Mode filter; Varactor diode; Tunable filter; Open loop; Band pass filter; Dual-mode resonator filter; Passband; Bias circuit
• ISSN: 0018-9480; 1557-9670
• DOI: 10.1109/TMTT.2010.2052958

This paper presents a new type of varactor-tuned dual-mode bandpass filter. Since the two operating modes (i.e., the odd and even modes) in a dual-mode microstrip open-loop resonator do not couple to each other, the tuning of the passband frequency becomes simple with a single dc-bias circuit while keeping nearly constant absolute bandwidth. Design equations and procedures are derived, and two two-pole tunable bandpass filters of this type are demonstrated experimentally.