A Novel Tri-Mode Bandwidth Tunable Filter With Harmonic Suppression

In this paper, a novel bandwidth reconflgurable bandpass fllter is proposed. Based on a varactor loaded tri-mode resonator consisted of one constant odd mode and two independent varactor- tuned even modes, each passband edge of the proposed fllter can be freely adjusted. By varying the reverse bias voltage applied to the varactor diode that is connected to the resonator, the bandwidth can be controlled conveniently. The resonant frequencies and Transmission Zeros (TZs) are derived and verifled by both theoretical analysis and simulation. Stepped Impedance Resonator (SIR) is introduced to optimize the harmonic suppression. Finally, the measurement of the fabricated fllter shows a fractional bandwidth tuning range of 11.4{ 32.0% with a center frequency of 1.75GHz, a quite low insertion loss of 0.4{1.1dB, and wideband harmonic suppression up to 6GHz. The measurement and simulated results show good agreement.