Design of a compact dual-band bandpass filter with DGS-SIR resonators

A compact dual-band bandpass filter is proposed in this paper. This dual-band bandpass filter consists of a 50-μ microstrip line with U-shaped slots on the top layer and two pairs of folded stepped impedance resonators (SIRs) with defected ground structure (DGS) on the bottom layer. The central frequency of the first passband, 3.7 GHz, is determined by the first pair of the DGS-SIR resonators; the central frequency of the second passband, 5.7 GHz, depends on the second pair of the DGS-SIR resonators. In addition, the proposed filter is fabricated on the substrate RO4003C, with the size of 46 mm × 18 mm. As for the measured results, with 3.7 GHz and 5.7 GHz for central frequencies, the insertion losses are 1.8 dB and 2.1 dB, respectively. Moreover, the measured return losses are 16.5 dB and 18.51 dB, respectively.