Miniaturized Tri-Band Bandpass Filter with Wide Stopband Using Stacked-Coupled SIDGS Resonators

In this paper, a compact tri-band bandpass filter (BPF) with wide stopband is proposed based on tri-resonance substrate-integrated defected ground structure (SIDGS). Such SIDGS is constituted by three SIDGS resonators with stacked-coupled scheme, which can not only introduce tri-resonance with wide stopband response, but also reduce the circuit size. Based on proposed mechanisms, a tri-band BPF operated at 2.37/3.57/5.34 GHz is implemented, fabricated, and measured. The measured results show that the fabricated BPF has a wide stopband up to 12 GHz with rejection level higher than 30 dB. Meanwhile, the core size of proposed BPF is about 0.19×0.16 λg², where λg is the microstrip guided wavelength at the center frequency of 2.37 GHz.