Design Method for Tunable Planar Bandpass Filters with Single-Bias Control and Wide Tunable Frequency Range

Taejun Lim, Akash Anand, James Chen, Xiaoguang Liu, Yongshik Lee

Research output: Contribution to journalArticlepeer-review

8 Citations (Scopus)


A design method for a frequency-tunable planar bandpass filter is demonstrated. With the method, all reasonators can be designed with identical capacitances, allowing the filter to be tuned with identical varactors using a single bias control. This allows not only low-cost fabrication, but also a simple structure and design procedure. Moreover, the filter is based on miniaturized transmission lines. Therefore, a wide tuning range is achieved with a small size and outstanding out-of-band response. Most importantly, the method facilitates the design of a filter to vary the fractional bandwidth in a predetermined way as the center frequency is tuned. Thus, a tunable filter can be designed not only to maintain the fractional bandwidth, but also to expand or to reduce the bandwidth as the frequency is tuned. The experimental results of a compact third-order bandpass filter based on CPW lines with a 0.11λ{g}× 0.8λ {g} size show a very wide frequency tuning range of 62.8% with a 3-dB fraction bandwidth that remains within 28.65± 1.55% and an outstanding spurious suppression of under -40 dB up to as high as 3f{0}.

Original languageEnglish
Article number9123979
Pages (from-to)221-225
Number of pages5
JournalIEEE Transactions on Circuits and Systems II: Express Briefs
Issue number1
Publication statusPublished - 2021 Jan

Bibliographical note

Funding Information:
Manuscript received May 18, 2020; accepted June 13, 2020. Date of publication June 24, 2020; date of current version December 21, 2020. This work was supported by the National Research Foundation of Korea (NRF) grant funded by the Korea Government (MSIT) under Grant 2020R1A2C1010251. This brief was recommended by Associate Editor Q. Liu. (Corresponding author: Yongshik Lee.) Taejun Lim and Yongshik Lee are with the Department of Electrical and Electronic Engineering, Yonsei University, Seoul 120-749, South Korea (e-mail:

Publisher Copyright:
© 2004-2012 IEEE.

All Science Journal Classification (ASJC) codes

  • Electrical and Electronic Engineering


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