Frequency Tunable Non-Reciprocal Bandpass Filter Using Time-Modulated Microstrip λg/2 Resonators

Xiaohu Wu, Mahmoud Nafe, Alejandro Alvarez Melcon, Juan Sebastian Gomez-Diaz, Xiaoguang Liu

Research output: Contribution to journalArticlepeer-review

4 Scopus citations


This brief presents a novel frequency reconfigurable microstrip non-reciprocal bandpass filter based on time-modulated microstrip \lambda _{g}/2 resonators. The modulation is achieved by loading both ends of the \lambda _{g}/2 transmission line resonators with time-modulated capacitors. The modulation voltage source is connected at the center of the resonator, where there is a natural voltage null, and a single inductor is used to further enhance the biasing isolation. The wideband nature of this isolation scheme enables the tuning of the devices over a wide frequency range. With more than 30-dB RF to modulation isolation, the proposed resonator structure also enables low insertion loss by eliminating RF signal leakage to the modulation ports. A 3-pole bandpass filter example is simulated and measured, showing a minimal insertion loss of 3.9dB, a 20-dB isolation bandwidth of 42MHz at 1.0GHz, and frequency tuning range of 885-1031MHz.

Original languageEnglish (US)
Article number9159682
Pages (from-to)667-671
Number of pages5
JournalIEEE Transactions on Circuits and Systems II: Express Briefs
Issue number2
StatePublished - Feb 2021


  • Bandpass filter (BPF)
  • isolator
  • magnetless
  • microstrip
  • non-reciprocal
  • time-invariant
  • time-modulated
  • tunable

ASJC Scopus subject areas

  • Electrical and Electronic Engineering


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