A tunable dual-passband filter based on improved ring resonator

Abstract

A miniaturized varactor-tuned microstrip bandpass filter (BPF) based on an improved ring resonator is presented in this paper. The proposed BPF is comprised of a ring as 1/2 λ resonator with two varactors in the middle section and a coupling scheme. The variation of coupling coefficient can be controlled by using a capacitor. The center frequency of the lower passband can be tuned from 3.2 to 3.9 GHz, while the center frequency of the upper passband is at 4.9 GHz and it is fixed during the process. Theoretical analysis and design approach are demonstrated. Finally, the predicted results are compared with measured data and good agreement is reported.

Keywords:

• ring resonator
• dual-passband filter
• tunable
• even- and odd-mode

Acknowledgment

This work was supported by the fundamental research funds for the Central Universities [K50511020013].