Compact tunable dual-band filter using SIRs without extra blocking capacitances

Abstract

A tunable dual-band microstrip filter using step-impedance resonators with harmonic suppression and compact size is presented in this paper. The second passband frequency of the filter can be flexibly controlled by tuning the bias voltage across the varactor whereas the first passband frequency is fixed. The structure is composed of couple lines and capacitive-loaded stepped-impedance resonator to provide frequency tunability and folded to reduce the size of the filter. The coupling scheme applied in this paper helps to reduce insertion loss and eliminate parasitic parameters, which is due to that extra blocking capacitances that are needless compared with the conventional coupling structure. To certify the validity, a prototype dual-band filter is designed, fabricated, and measured. The measured results show good agreement with the simulated ones.

Acknowledgment

This work was supported by the Fundamental Research Funds for the Central Universities (K50511020021).