Tunable balanced bandpass filter with constant bandwidth and high common-mode suppression

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  • Yuan Chun Li
  • Quan Xue


Original languageEnglish
Article number5978807
Pages (from-to)2452-2460
Journal / PublicationIEEE Transactions on Microwave Theory and Techniques
Issue number10 PART 1
Publication statusPublished - 2011


This paper presents tunable balanced bandpass filters with constant fractional bandwidth (FBW) and constant absolute bandwidth (ABW), respectively. The equivalent differential- and common-mode circuits of the proposed filters are analyzed. The differential-mode bandwidths can be maintained constant when the frequency is tuned by selecting proper coupling regions and controlling the external quality factor Qe. To suppress the common-mode response, different elements are loaded in the middle of the resonators to misalign common-mode resonant frequencies. The common-mode response can be suppressed without degrading the differential-mode performance. For demonstration, two tunable balanced filters with constant FBW and ABW are implemented, respectively. Comparisons of the calculated, simulated, and measured results are presented to verify the theoretical predications. © 1963-2012 IEEE.

Research Area(s)

  • Balanced filter, common-mode suppression, constant bandwidth, differential-mode, external quality factor, tunable filter