Tunable Dual-Band Bandpass Filter Using Varactor-Loaded Short-Ended Resonators

A novel planar tunable bandpass filter using the centrally-loaded short-ended resonator is presented in this paper. Characterized by theoretical analysis, the proposed structure is founded to have the advantage that the fundamental frequency can be tuned while the second harmonic remains almost unchanged. By controlling the voltage, the lower passband can be tuned in a wide frequency range. To demonstrate the purposed idea, a dual-band bandpass filter is implemented with the tunable lower passband and fixed upper passband. The experimental results are presented to verify the proposed method.