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.
2. Liu, H.-W., L.-Y. Li, X.-H. Li, and S.-X. Wang, "Compact microstrip lowpass filter using asymmetric stepped-impedance hairpin resonator and slotted ground plane," Journal of Electromagnetic Waves and Applications, Vol. 22, No. 11--12, 1615-1622, 2008.
3. Sharma, R., T. Chakravarty, S. Bhooshan, and A. B. Bhattacharyya, "Design of a novel 3 dB microstrip backward wave coupler using defected ground structure," Progress In Electromagnetics Research, Vol. 65, 261-273, 2006.
4. Ahn, D., J. S. Park, C. S. Kim, Y. Qian, and T. Itoh, "A design of the low pass filter using the novel microstrip defected ground structure," IEEE Trans. Microwave Theory Tech., Vol. 49, 86-93, 2001.
5. Yang, M. H., J. Xu, Q. Zhao, L. Peng, and G. P. Li, "Compact, broad-stopband lowpass filters using SIRS-loaded circular hairpin resonators," Progress In Electromagnetics Research, Vol. 102, 95-106, 2010.
6. Yang, M. H., J. Xu, Q. Zhao, and X. Sun, "Wide-stopband and miniarurized lowpass filters using sirs-loaded hairpin resonators," Journal of Electromagnetic Waves and Applications, Vol. 23, No. 17--18, 2385-2396, 2009.
7. Park, J. S., J. H. Kim, J. H. Lee, S. H. Kim, and S. H. Myung, "A novel equivalent circuit and modeling method for defected ground structure and its application to optimization of a DGS low pass filter," IEEE Int. Microwave Symp. Digest, Vol. 1, 417-420, 2002.
8. Cho, J. H. and J. C. Lee, "Microstrip stepped-impedance hairpin resonator low-pass filter with defected ground structure," Microwave Opt. Technol. Lett., 405-408, 2006.
9. Fu, S., C. Tong, X. Li, W. Zhang, and K. Shen, "Compact miniaturized stepped-impedance lowpass filter with sharp cutoff characteristics," Microwave Opt. Technol. Lett., 2257-2258, 2009.
10. Wu, B., B. Li, and C. Liang, "Design of low-loss filter using novel split-ring resonator defected ground structure," Microwave Opt. Technol. Lett., Vol. 49, 288-291, 2007.
11. Kuo, J. T., M. J. Maa, and P. H. Lu, "Microstrip elliptic function filters with compact miniaturized hairpin resonators," Asia-Pacific Microwave Conf. Proc., Vol. 2, 860-864, 1999.
12. Garde, I., M. J. Yabar, and C. del Rio, "Sample modeling of dgs to design 1 d-pbg low-pass filters," Microwave Opt. Technol. Lett., Vol. 37, 228-232, 2003.
13. Chen, J., Z.-B.Weng, Y.-C. Jiao, and F.-S. Zhang, "Lowpass filter design of Hilbert curve ring defected ground structure," Progress In Electromagnetics Research, Vol. 70, 269-280, 2007.