Electronically switchable bandpass filters using loaded stepped-impedance resonators

Shih Fong Chao*, Chao Huang Wu, Zuo-Min Tsai , Huei Wang, Chun Hsiung Chen

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

73 Scopus citations


Stepped-impedance resonators with diodes loaded at one end are used to develop switchable bandpass filters in this paper. The loaded diodes are used to switch the resonance conditions of the stepped-impedance resonators. The equations for resonance conditions of the stepped-impedance resonators with different loads at one end are derived and discussed. With these derived equations, the switchable filters can be easily designed and synthesized using the coupled-resonator filter theory. When the switchable filter is switched on, a bandpass filter response with a wide stopband rejection is achieved by making the on-state coupled resonators have the same fundamental resonant frequency, but different higher order resonant frequencies. When switched off, a high and wideband isolation is obtained by properly misaligning the resonant modes of the off-state resonators. The design concept is demonstrated by two single-pole-single-throw fourth-order Butterworth-type switchable microstrip bandpass filters, which utilize two and three switched stepped-impedance resonators, respectively. Finally, a compact single-pole-double-throw switchable microstrip bandpass filter using common resonators is demonstrated for wireless communication applications.

Original languageEnglish
Pages (from-to)4193-4201
Number of pages9
JournalIEEE Transactions on Microwave Theory and Techniques
Issue number12
StatePublished - 1 Dec 2006


  • Coupled-resonator bandpass filter
  • Stepped-impedance resonator
  • Switch
  • Switchable filter

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