Independently Tunable Compact Dual-Band Bandpass Filter With High Selectivity and Wide Stopband Using Multilayer Folded Dual-Mode SIDGS Resonator

In this paper, a multilayer folded substrate-integrated defected ground structure (SIDGS) resonator is proposed for tunable dual-band bandpass filter (BPF) design. Such miniaturized resonator allocates two independently tunable resonant modes. In addition, lowpass units (LPUs) are embedded in the microstrip feed-lines to further improve the stopband rejection level. To verify the mechanism, a tunable dual-band BPF is fabricated and measured. The first passband can be tuned from 0.94 to 1.12 GHz, while the second passband varies from 2.29 to 2.92 GHz. The proposed dual-band BPF features high selectivity with a compact size (i.e., 15.4 mm × 15.6 mm). Besides, it exhibits a stopband rejection of 22 dB up to 13.9 GHz for all tuning cases.