Dual-Band Bandpass Filter with Ultra-Wide Upper Stopband Using Slow-Wave Dual-Resonance Cells
A dual-band bandpass filter (BPF) with ultra-wide upper stopband based on slow-wave dual-resonance cells is presented. The broadside-coupled resonant cell is composed of a microstrip T-stub, a slot-line, and a meander stepped-impedance defected ground structure (DGS). Such DGS and slot-line located under the microstrip T-stub can produce a dual-resonance (i.e., f1 and f2) with a compact structure. Moreover, the strong slow-wave effect can be introduced by the proposed cell, which leads to an ultrawide upper-stopband bandpass filtering response. To verify the operational mechanisms, an ultrawide upper-stopband BPF with two passbands centered at 3.15 and 3.85 GHz is designed and fabricated, which exhibits a upper-stopband more than 11.5 times of the first resonance f1 with a 29.8-dB rejection level.