An asymmetric stepped-impedance ring resonator (ASIRR) is proposed for the design of a triple-bandpass filter. This resonator is applied to creat the former two passbands by utilizing a stepped-impedance circular ring and the third passband by introducing two asymmetric coupling structures. It is found that the S-parameter performance can be improved by adding a pair of shorted and open stubs, the second passband and the stopbands on both sides of the third passband can be tuned by adjusting the length of open stubs. A prototype filter operating at 1.04, 3.52 and 5.57 GHz is designed, fabricated, and measured with the corresponding fractional bandwidths of 23.1%, 7.4%, and 4.1%. Good agreements between the simulated and measured results are achieved for the ASIRR filter. Also, four transmission zeros are generated.
2. Xiao, J. K., Y. Li, J. G. Ma, and X. P. Bai, "Transmission zero controllable bandpass filters with dual and quad-band," Electron. Lett., Vol. 51, No. 13, 1003-1005, 2015.
3. Xiao, J. K., Y. F. Zhu, Y. Li, and X. W. Li, "Miniature quad-band bandpass filter with passband individually controllable using folded SIR," Electron. Lett., Vol. 50, No. 9, 679-680, 2014.
4. Zhang, S. and L. Zhu, "Synthesis design of dual-band bandpass filters with λ/4 stepped-impedance resonators," IEEE Trans. Microw. Theory Techn., Vol. 61, No. 5, 1812-1819, 2013.
5. Wu, H. W. and R. Y. Yang, "Design of a triple-passband microstrip bandpass filter with compact size," Journal of Electromagnetic Waves and Applications, Vol. 24, No. 17–18, 2333-2341, 2010.
6. Hsu, C. I. G., C. H. Lee, and Y. H. Hsieh, "Tri-band bandpass filter with sharp passband skirts designed using tri-section SIRs," IEEE Microw. Wireless Compon. Lett., Vol. 18, No. 1, 19-21, 2008.
7. Chu, Q. X. and X. M. Lin, "Advanced triple-band bandpass filter using trisection SIR," Electron. Lett., Vol. 44, No. 4, 295-296, 2008.
8. Wei, X., P. Wang, P. Gao, Z. Xu, J. Liao, and Y. Shi, "Compact tri-band bandpass filter using open stub loaded trisection λ/4 stepped impedance resonator," IEEE Microw. Wireless Compon. Lett., Vol. 24, No. 8, 512-514, 2014.
9. Xu, K., Y. Zhang, D. Li, Y. Fan, J. L.-W. Li, W. T. Joines, and Q. H. Liu, "Novel design of a compact triple-band bandpass filter using short stub-loaded SIRs and embedded SIRs structure," Progress In Electromagnetics Research, Vol. 142, 309-320, 2013.
10. Chen, W. Y., M. H. Weng, S. J. Chang, H. Kuan, and Y. H. Su, "A new tri-band bandpass filter for GSM, WiMAX and ultra-wideband responses by using asymmetric stepped impedance resonators," Progress In Electromagnetics Research, Vol. 124, 365-381, 2012.
11. Liu, Y., W.-B. Dou, and Y.-J. Zhao, "A tri-band bandpass filter realized using tri-mode T-shape branches," Progress In Electromagnetics Research, Vol. 105, 425-444, 2010.
12. Zhu, C., J. Xu, W. Kang, and W. Xu, "High-selectivity tri-band bandpass filter with ultra-wide stopband," Electron. Lett., Vol. 51, No. 20, 1585-1587, 2015.
13. Kumar, N. and Y. K. Singh, "Compact tri-band bandpass filter using three stub-loaded open-loop resonator with wide stopband and improved bandwidth response," Electron. Lett., Vol. 50, No. 25, 1950-1952, 2014.
14. Mokhtarri, M., J. Borenemann, K. Rambabu, and S. Amari, "Coupling-matrix design of dual and triple passband filters," IEEE Trans. Microw. Theory Techn., Vol. 54, No. 11, 3940-3946, 2006.
15. Wang, W., Q. Cao, C. Yang, Y. Wang, and Y. Chen, "Design of dual-bandpass filters using stepped-impedance circular ring resonator," Electron. Lett., Vol. 51, No. 25, 2117-2119, 2015.
16. Kuo, J. T. and C. Y. Tsai, "Periodic stepped-impedance ring resonator (PSIRR) bandpass filter with a miniaturized area and desirable upper stopband characteristics," IEEE Trans. Microw. Theory. Techn., Vol. 54, No. 3, 1107-1112, 2006.