In this paper, a compact stepped-impedance hairpin resonator (SIHR) low-pass filter (LPF) with an improved split-ring resonator defected ground structure (ISRR DGS) and two elliptical DGSs is presented. The proposed LPF exhibits the advantages of low insertion loss, sharp cutoff characteristic, wide stopband over the ordinary LPFs. The introduced DGSs are presented to improve the in-band and out-band characteristic. An equivalent RLC circuit model of the two kinds of DGSs is presented and analyzed. Combining with these two structures, a new SIHR LPF having 3-dB cutoff frequency of 2.5 GHz is fabricated and measured. Measured results show that the selectivity of the proposed LPF is more than 100 dB/GHz and the insertion loss is less than 0.5 dB in the passband. A wide stop-band bandwidth with 20 dB attenuation from 2.58 up to 7.5 GHz is achieved. Moreover, the occupied area is only 20×25 mm2.
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