Dual-Band Bandpass Filter Using Varactor Loaded Square Split Ring Resonator

A dual-band bandpass filter (BPF) using varactor-loaded square split ring resonator is proposed to realize the dual-band frequency response and one high-selective tunable passband. This resonator is mainly composed of a pair of the square split ring, two varactors and an open stub (l=λ/4@f
_even
). By placing an open stub at the center position of the proposed resonator, the odd-mode resonance fodd is split into two modes, as f
_odd1
and f
_odd2
, which can be used to form a high-selectivity passband. The two distinct odd/even-mode resonances can be generated independently and used to realize the first-/second-passbands. The simulated results indicate that the center frequency of the first-passband can be tuned from 1.15 to 1.45 GHz with a 3-dB constant bandwidth of 110±10 MHz. meanwhile, the center frequency of the second-passband is fixed at 2.2 GHz with a 3-dB fractional bandwidth of 8.6-11.4%.