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

A bandpass filter (BPF) with wide upper stopband and low radiation loss based on a 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. The proposed slow-wave SIDGS cells can introduce the passband resonances with a wide upper stopband. Besides, the converged ground with metal-vias surrounding the SIDGS could suppress the radiation loss, which is flexible for integration. To verify the operational mechanisms, a wide upper stopband BPF with a passband centered at 2.4 GHz is developed and fabricated. The measured stopband is up to 19.3 GHz with a 29 dB rejection level, while the whole loss (i.e., including radiation, metal, and substrate loss) is less than 30% up to 19 GHz. The core circuit-size of the BPF is about 0.16 λg by 0.16 λg, where λg is the microstrip guided wavelength at 2.4 GHz.