Compact electronically tunable microstrip dual-band filter using stub-loaded SIRs

Abstract

A compact electronically tunable dual-bandpass filter (BPF) with harmonic suppression is investigated in this paper. The BPF is composed of a step-impedance resonator, a T-stub with a varactor diode and a filtering network. The second passband can be independently tuned by varying the bias voltage across the varactor, whereas the first passband is fixed. The proposed filter exhibits wide stopband due to the introduction of the filtering network suppressing harmonics. A prototype of a tunable dual-band BPF, in which the second passband is tuned from 1.58 to 2.21 GHz and the first passband is fixed at 0.98 GHz, is designed and fabricated. The simulated and measured results are in good agreement with each other.

Keywords:

• step-impedance resonator (SIR)
• tunable filter
• varactor diode
• wide stopband

Acknowledgments

This work was supported by the fundamental research funds for the Central Universities (K50511020021), and the National Science Foundation of China under Grant 61201298 and 61203202.