In this letter, a novel compact tri-band bandpass filter (BPF) with high selectivity is presented. The proposed tri-band performance measure is realized by using eight sets of resonators, i.e., two- and three-section stepped impedance resonators (SIRs). The three-section SIR is designed for determining the three passbands and providing the electric coupling, while the two-section SIR is used for determining each passband respectively and providing the magnetic coupling. Then, coupling structures with two transmission zeros near each passband edge are presented, therefore, the band selectivity of the filter is much improved. The three passband frequencies could be independently designed and tuned. This novel tri-band BPF is fabricated and the measured results are in good agreement with the full-wave simulation results.
2. Weng, M.-H. and H.-W. Wu, "A novel triple-band bandpass filter using multilayer-based substrates for WiMAX," Proc. Eur. Microw. Conf., 325-328, Oct. 2007.
3. Ren, L.-Y., "Tri-band bandpass flters based on dual-plane microstrip/DGS Slot Structure," IEEE Microw. Wirel. Compon. Lett., Vol. 20, No. 8, 429-431, 2010.
4. Zhang, X.-Z., Q. Xue, and B.-J. Hu, "Planar tri-band bandpass filter with compact size," IEEE Microw. Wirel. Compon. Lett., Vol. 20, No. 5, 262-264, 2010.
5. Chen, F.-C., Q.-X. Chu, and Z.-H. Tu, "Tri-band bandpass filter using stub loaded resonators," Electron. Lett., Vol. 44, No. 12, 747-749, Jun. 2008.
6. Wang, X.-H., B.-Z. Wang, and K. J. Chen, "Compact broadband dual-band bandpass filters using slotted ground structures," Progress In Electromagnetics Research, Vol. 82, 151-166, 2008.
7. Fan, J.-W., C.-H. Liang, and X.-W. Dai, "Design of cross-coupled dual-band filter with equal-length split-ring resonators," Progress In Electromagnetics Research, Vol. 75, 285-293, 2007.
8. Wu, M.-S., Y.-Z. Chueh, J.-C. Yeh, and S.-G. Mao, "Synthesis of triple-band and quad-band bandpass filters using lumped-element coplanar waveguide resonators," Progress In Electromagnetics Research B, Vol. 13, 433-451, 2009.
9. 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.
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. Lin, W.-J., C.-S. Chang, J.-Y. Li, D.-B. Lin, L.-S. Chen, and M.-P. Houng, "A new approach of dual-band filters by stepped impedance simplified cascaded quadruplet resonators with slot coupling," Progress In Electromagnetics Research Letters, Vol. 9, 19-28, 2009.
12. Wu, G.-L., W. Mu, X.-W. Dai, and Y.-C. Jiao, "Design of novel dual-band bandpass filter with microstrip meander-loop resonator and CSRR DGS," Progress In Electromagnetics Research, Vol. 78, 17-24, 2008.
13. De Paco, P., O. Menendez, and J. Marin, "Dual-band filter using non-bianisotropic split-ring resonators," Progress In Electromagnetics Research Letters, Vol. 13, 51-58, 2010.
14. Sagawa, M., M. Makimoto, and S. Yamashita, "Geometrical structures and fundamental characteristics of microwave stepped-impedance resonators," IEEE Trans. on Microw. Theory and Tech., Vol. 45, No. 7, 1078-1084, 2002.
15. Lin, X. M. and Q. X. Chu, "Design of triple-band bandpass filter using tri-section stepped-impedance resonators," Proc. Int. Microw. Millimeter Wave Tech. Conf., 798-800, Guilin, China, Apr. 2007.
16. Chu, Q. X. and X. M. Lin, "Advanced triple-band bandpass filter using tri-section SIR," Electron. Lett., Vol. 44, No. 4, 295-296, Feb. 2008.
17. Luo, S., L. Zhu, and S. Sun, "Compact dual-mode triple-band bandpass filters using three pairs of degenerate modes in a ring resonator," IEEE Trans. on Microw. Theory and Tech., Vol. 59, No. 5, 1222-1229, May 2011.
18. Chen, F. C. and Q. X. Chu, "Design of compact tri-band bandpass filters using assembled resonators," IEEE Microw. Theory Tech., Vol. 57, No. 1, 165-171, Jan. 2009.
19. Hong, J.-S. and M. J. Lancaster, "Microstrip Filters for RF/Microwave Applications," Wiley, New York, 2001.