Dual-Band Bandpass Filter With Independently Tunable Center Frequencies and Bandwidths

• Published in: IEEE transactions on microwave theory and techniques Vol. 61; no. 1; pp. 107 - 116
• Main Authors: Chaudhary, G., Yongchae Jeong, Jongsik Lim
• Format: Journal Article
• Language: English
• Published: New York, NY IEEE 01.01.2013; Institute of Electrical and Electronics Engineers; The Institute of Electrical and Electronics Engineers, Inc. (IEEE)
• Subjects: Applied sciences; Band pass filters; Bandwidth; Circuit properties; Defected ground structure (DGS); Dual band; Electric, optical and optoelectronic circuits; Electronic circuits; Electronics; Exact sciences and technology; Frequency filters; harmonics suppression; Microwave circuits, microwave integrated circuits, microwave transmission lines, submillimeter wave circuits; Oscillators, resonators, synthetizers; Passband; Resonant frequency; tunable bandpass filter; Tuning; varactor diode; Varactors; Harmonic; tunable bandpass filter; Tunable circuit; Resonator; Defected ground structure; Tuning; Multi-band circuit; Degradation; Mode filter; Harmonics suppression; dual-band; Varactor diode; Transmission line; Tunable filter; Antenna feeds; Band pass filter; Transmission mode; Defected ground structure (DGS); Passband; Damaging
• ISSN: 0018-9480; 1557-9670
• DOI: 10.1109/TMTT.2012.2222910

This paper presents a novel approach to the design of tunable dual-band bandpass filter (BPF) with independently tunable passband center frequencies and bandwidths. The newly proposed dual-band filter principally comprises two dual-mode single band filters using common input/output lines. Each single BPF is realized using a varactor-loaded transmission-line dual-mode resonator. The proposed filter also offers switchable characteristics to select either of the passbands (either the first or the second passband only). To suppress the harmonics over a broad bandwidth, defected ground structures are used at input/output feeding lines without degrading the passbands characteristics. From the experimental results, it was found that the proposed filter exhibited the first passband center frequency tunable range from 1.48 to 1.8 GHz with a 3-dB fractional bandwidth (FBW) variation from 5.76% to 8.55% and the second passband center frequency tunable range from 2.40 to 2.88 GHz with the 3-dB FBW variation from 8.28% to 12.42%. The measured harmonic results of the proposed filters showed a rejection level of 19 dB, which is up to more than ten times of the highest center frequency of the first passband without degradation of the passbands.