This paper presents two dual-band bandpass filters with controllable passband frequencies and bandwidths. The filters are realized utilizing a novel quad-mode stub-loaded ring resonator. All the four mode equivalent circuits of the resonator are quarter-wavelength resonators, and their fundamental resonance frequencies are used to form the passbands. So the designed filters have a compact circuit size and relatively wide upper stopband. For validation, two experimental filters operating at 1.5/2.4 GHz and 1.5/3.5 GHz are designed. In the design of the second filter, hook-shape feed-lines and source-load coupling are applied to generate more transmission zeros, which greatly improve the selectivity of the filter. Finally, the filters are fabricated, and measured. The measured results have good agreement with the simulated ones.
2. Yang, S., L. Lin, J.-Z. Chen, K. Deng, and C.-H. Liang, "Design of compact dual-band bandpass filter using dual-mode stepped-impedance stub resonator," Electronics Letters, Vol. 50, No. 8, 611-613, Apr. 2014.
3. Sun, S.-J., T. Su, K. Deng, B. Wu, and C.-H. Liang, "Shorted-ended stepped-impedance dual-resonance resonator and its application to bandpass filters," IEEE Trans. Microw. Theory Tech., Vol. 61, No. 9, 3209-3215, Sep. 2013.
4. Zhang, X. Y., C.-H. Chan, Q. Xue, and B.-J. Hu, "Dual-band bandpass filter with controllable bandwidths using two coupling paths," IEEE Microw. Wireless Compon. Lett., Vol. 20, No. 11, 616-618, Nov. 2010.
5. Kuo, J.-T. and S.-W. Lai, "New dual-band bandpass filter with wide upper rejection band," Progress In Electromagnetics Research, Vol. 123, 371-384, 2012.
6. Zhang, X. Y., J.-X. Chen, Q. Xue, and S.-M. Li, "Dual-band bandpass filters using stub-loaded resonators," IEEE Microw. Wireless Compon. Lett., Vol. 17, No. 8, 583-585, Aug. 2007.
7. Ma, D., Z. Y. Xiao, L. Xiang, X. Wu, C. Huang, and X. Kuo, "Compact dual-band bandpass filter using folded SIR with two stubs for WLAN," Progress In Electromagnetics Research, Vol. 117, 357-364, 2011.
8. Kuo, J.-T., S.-C. Tang, and S.-H. Lin, "Quasi-elliptic function bandpass filter with upper stopband extension and high rejection level using cross-coupled stepped-impedance resonators," Progress In Electromagnetics Research, Vol. 114, 395-405, 2011.
9. Chu, Q. X. and F. C. Chen, "A compact dual-band bandpass filter using meandering stepped impedance resonators," IEEE Microw. Wireless Compon. Lett., Vol. 18, No. 5, 320-322, May 2008.
10. Yao, Z., C. Wang, and N. Y. Kim, "A Compact dual-mode dual-band bandpass filter using stepped-impedance open-loop resonators and center-loaded resonators," Microw. Opt. Technol. Lett., Vol. 55, No. 12, 3000-3005, Dec. 2013.
11. Sun, S.-J., T. Su, K. Deng, B.Wu, and C.-H. Liang, "Compact microstrip dual-band bandpass filter using a novel stub-loaded quad-mode resonator," IEEE Microw. Wireless Compon. Lett., Vol. 23, No. 9, 465-467, Nov. 2013.
12. Jiang, W., L. Zhou, A.-M. Gao, W. Shen, W.-Y. Yin, and J.-F. Mao, "Compact dual-mode dual-band balun filter using double-sided parallel-strip line," Electronics Letters, Vol. 48, No. 21, 1351-1352, Oct. 2012.
13. Fu, S., B.Wu, J. Chen, S.-J. Sun, and C. H. Liang, "Novel second-order dual-mode dual-band filters using capacitance loaded square loop resonator," IEEE Trans. Microw. Theory Tech., Vol. 60, No. 3, 477-483, Mar. 2012.
14. Sung, Y., "Dual-mode dual-band filter with band notch structures," IEEE Microw. Wireless Compon. Lett., Vol. 20, No. 2, 73-75, Feb. 2010.
15. Li, Y.-C., H. Wong, and Q. Xue, "Dual-mode dual-band bandpass filter based on a stub-loaded patch resonator," IEEE Microw. Wireless Compon. Lett., Vol. 21, No. 10, 525-527, Oct. 2011.
16. Chiou, Y.-C., P.-S. Yang, J.-T. Kuo, and C.-Y. Wu, "Transmission zero design graph for dual-mode dual-band filter with periodic stepped-impedance ring resonator," Progress In Electromagnetics Research, Vol. 108, 23-36, 2010.
17. Zhao, L.-P., D. Li, Z.-X. Chen, and C.-H. Liang, "Novel design of dual-mode dual-band bandpass filter with triangular resonators," Progress In Electromagnetics Research, Vol. 77, 417-424, 2007.
18. Luo, S. and L. Zhu, "A novel dual-mode dual-band bandpass filter based on a single ring resonator," IEEE Microw. Wireless Compon. Lett., Vol. 19, No. 8, 497-499, Aug. 2009.
19. Belyaev, B. A., A. M. Serzhantov, and V. V. Tyurnev, "A miniature dual-band filter based on microstrip dual-mode resonators," Technical Physics Letters, Vol. 38, No. 9, 839-842, 2012.
20. Belyaev, B. A., A. M. Serzhantov, and V. V. Tyurnev, "A dual-mode split microstrip resonator and its applications in frequency selective devices," Microw. Opt. Technol. Lett., Vol. 55, No. 9, 2186-2190, 2013.
21. Sun, S., "A dual-band bandpass filter using a single dual-mode ring resonator," IEEE Microw. Wireless Compon. Lett., Vol. 21, No. 6, 298-300, Jun. 2011.