In this paper, a compact quad-channel diplexer utilizing quad-mode stub-loaded resonators (QMSLRs) is proposed. The proposed quad-channel diplexer is composed of two dual-band bandpass filters (BPFs) based on QMSLRs and source-load coupling lines. Due to the symmetry of the proposed quad-mode resonator, its resonance characteristics are analyzed by using the even-odd-mode method twice. All four modes equivalent circuits of the resonator are quarter wavelength resonators, so the circuit size can be very compact, and the first resonance frequencies is three times of the fundamental ones. Stub-to-stub coupling is introduced to split two identical resonance modes, which is in favor of implementing dual-band BPF by using a single quad-mode resonator. By tuning the corresponding physical dimensions of the stubs, the resonant modes can be individually adjusted. The source-load coupling lines are properly designed to provide appropriate external coupling for the passbands and high isolation level between channels. For demonstration, a quad-channel diplexer (0.9/1.2 GHz at Load 1 and 1.5/1.8 GHz at Load 2) using the quad-mode resonator is designed, fabricated and measured. The simulated and measured results with good agreement are presented.
2. Chen, X. W., W.-M. Zhang, and C.-H. Yao, "Design of microstrip diplexer with wide band-stop," International Conference on Microwave and Millimeter Wave Technology, 1-3, 2007.
3. Xu, W. Q., M.-H. Ho, and C.-G. Hsu, "UMTS diplexer design using dual-mode stripline ring resonators," Electronics Letters, Vol. 43, No. 13, 721-722, Jun. 2007.
4. Tsai, C. M., S.-Y. Lee, C.-C. Chuang, and C.-C. Tsai, "A folded coupled-line structure and its application to filter and diplexer design," IEEE MTT-S Int. Microw. Symp. Dig., 1927-1930, Jun. 2002.
5. 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.
6. Yang, R.-Y., C.-M. Hsiung, C.-Y. Hung, and C.-C. Lin, "Design of a high band isolation diplexer for GPS and WLAN system using modified stepped-impedance resonators," Progress In Electromagnetics Research, Vol. 107, 101-114, 2010.
7. Huang, C.-Y., M.-H. Weng, C.-S. Ye, and Y.-X. Xu, "A high band isolation and wide stopband diplexer using dual-mode stepped-impedance resonators," Progress In Electromagnetics Research, Vol. 100, 299-308, 2010.
8. Yu, W. H., J.-C. Mou, X. Li, and X. Lv, "A compact filter with sharp-transition and wideband-rejection using the novel defected ground structure," Journal of Electromagnetic Waves and Applications, Vol. 23, No. 2-3, 329-340, 2009.
9. Gu, Y. C., L.-H. Weng, and X.-W. Shi, "An improved microstrip open-loop resonator bandpass filter with DGSS for WLAN application," Journal of Electromagnetic Waves and Applications, Vol. 23, No. 4, 463-472, 2009.
10. Chen, C. F., T.-Y. Huang, C.-P. Chou, and R.-B. Wu, "Microstrip diplexers design with common resonator sections for compact size, but high isolation," IEEE Trans. Microw. Theory Tech., Vol. 54, No. 5, 1011-1018, 2006.
11. Chuang, L. M. and M.-T. Wu, "Microstrip diplexer design using common T-shaped resonator," IEEE Microw. and Wirel. Compon. Lett., Vol. 21, No. 11, 583-585, 2011.
12. Liu, H. W., W.-Y. Xu, Z.-C. Zhang, and X.-H. Guan, "Compact diplexer using slotline stepped impedance resonator," IEEE Microw. and Wirel. Compon. Lett., Vol. 23, No. 2, 75-77, 2013.
13. Skaik, T. F., M.-J. Lancaster, and F. Huang, "Synthesis of multiple output coupled resonator circuits using coupling matrix optimisation," IET Microwaves, Antennas and Propagation, Vol. 5, No. 9, 1081-1088, 2011.
14. Skaik, T. F. and M.-J. Lancaster, "Coupled resonator diplexer without external junctions," Journal of Electromagnetic Analysis and Applications, Vol. 3, No. 6, 238-241, 2011.
15. An, J., G.-M. Wang, C.-X. Zhang, and P. Zhang, "Diplexer using composite right-/left-handed transmission line," Electronics Letters, Vol. 44, No. 11, 685-687, 2008.
16. Garcia-Lamperez, A., M. Salazar-Palma, and T.-K. Sarkar, "Analytical synthesis of microwave multiport networks," IEEE MTT-S Int. Microwave Symp. Digest, 455-458, 2004.
17. Xue, Q. and J.-X. Chen, "Compact diplexer based on double-sided parallel-strip line," Electronics Letters, Vol. 44, No. 2, 123-124, 2008.
18. Tyurnev, V. V. and A. M. Serzhantov, "Dual-mode split microstrip resonator for compact narrowband bandpass filters," Progress In Electromagnetics Research C, Vol. 23, 151-160, 2011.
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 microstrip diplexer based on dual-mode resonators," Technical Physics Letters, Vol. 38, No. 8, 743-746, 2012.
21. Belyaev, B. A., A. M. Serzhantov, and V. V. Tyurnev, "A dual-mode split microstrip resonator and its applications in frequency selective devices," Microwave and Optical Technology Letters, Vol. 55, No. 9, 2186-2190, 2013.
22. Hong, S. and K. Chang, "A 10-35-GHz six-channel microstrip multiplexer for wide-band communication systems," IEEE Trans. Microw. Theory Tech., Vol. 54, No. 4, 1370-1378, 2006.
23. Zhang, S. and L. Zhu, "Compact and high-selectivity microstrip bandpass filters using triple-/quad-mode stub-loaded resonators," IEEE Microw. and Wirel. Compon. Lett., Vol. 21, No. 10, 522-524, 2011.
24. Kuo, J. T. and E. Shih, "Microstrip stepped impedance resonator bandpass filter with an extended optimal rejection bandwidth," IEEE Trans. Microw. Theory Tech., Vol. 51, No. 5, 1554-1559, 2003.