Compact Bandpass Filter with Wide Stopband and Low Radiation Loss Using Substrate Integrated Defected Ground Structure

In this paper, a bandpass filter (BPF) with wide upper stopband and low radiation loss based on the substrate integrated defected ground structure (SIDGS) is presented. The BPF is composed of two sets of stepped-impedance SIDGS resonant cells with two microstrip feed-lines. Such slow-wave SIDGS cells can introduce the passband resonances with a wide upper stopband. Besides, the SIDGS surrounded by the bottom ground layer with metal-vias can not only suppress the radiation loss but also can be flexible for integration. To verify the mechanisms mentioned above, a wide upper stopband BPF with a passband centered at 2.4 GHz (i.e., f0) is implemented and fabricated. The measured stopband is up to 19.3 GHz (i.e., 8f0) with a rejection level of 29 dB, while the total loss (i.e., including radiation, metal, and substrate loss) is less than 30% up to 19 GHz. The core size of the BPF is about 0.16 λg × 0.16 λg, where λg is the microstrip guided wavelength at the center frequency.