An analytic design method for microstrip tunable filters

Juseop Lee, Kamal Sarabandi

Research output: Contribution to journalArticlepeer-review

37 Citations (Scopus)


This paper describes an analytic design procedure for microstrip tunable filters. Step-impedance resonators are employed and loaded with varactors for achieving agility in the filter response. Fixed lumped capacitors are utilized as admittance inverters in order to minimize the number of varactors in the filter. An analytic approach for filter design makes it possible to achieve a tunable filter showing the same frequency response when the center frequency is adjusted. A two-pole microstrip tunable filter whose center frequency can be adjusted from 1.1 to 1.5 GHz is designed to demonstrate the validity of design theory. A prototype tunable filter operating from 2.1 to 2.7 GHz is also designed and measured. A good agreement between the measured and simulated results is shown. Finally, three- and four-pole tunable filters are designed to show straightforward application of the presented design method to higher order tunable filter design.

Original languageEnglish
Article number4545889
Pages (from-to)1699-1706
Number of pages8
JournalIEEE Transactions on Microwave Theory and Techniques
Issue number7
Publication statusPublished - 2008 Jul
Externally publishedYes


  • Microwave filters
  • Tunable filters
  • Varactor

ASJC Scopus subject areas

  • Radiation
  • Condensed Matter Physics
  • Electrical and Electronic Engineering


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