A new uni-planar structure branch-line coupler with broad bandpass response is proposed. Single section branch line couplers (SSBC) are popular due to their simplicity and ease of use but suffer from narrow return loss bandwidth and poor out of band rejection characteristics. The work presented here overcomes these limitations with the use of coupled port feeding. Through the study of input impedance of feeding network and single section branch line coupler, the bandwidth of the new coupler increased by almost 6-times. In addition, the coupler exhibited band-pass filtering characteristics. Measured results exhibited low insertion loss (≤4-dB), small magnitude difference (≤1-dB), good return loss and isolation (≥10-dB) and small phase variation (90°±5) within the passband. A measured bandwidth of 58% was achieved with this single section coupled port fed branch line coupler at a centre frequency of 1-GHz. Its two output ports achieved rejection levels better than 25 dB in the stopband.
1. Sergio, L.-R., G.-L. Alejandro, S.-P. Magdalena, D.-E. Ana Isabel, G.-V. Juan Sebastian, and P.-C. Manuel Jesua, "Microstrip filter and power divider with improved out-of-band rejection for a Ku-band input multiplexer," Microwave Conference, (EuMC), 315-318, Munich, Germany, Oct. 2003.
2. Riblet, G. P., "A directional coupler with very flat coupling," IEEE Trans. Microw. Theory Tech., Vol. 26, No. 2, 70-74, Feb. 1978. doi:10.1109/TMTT.1978.1129315
3. Muraguchi, M., T. Yukitake, and Y. Naito, "Optimum design of 3 dB branch-line couplers using microstrip lines," IEEE Trans. Microw. Theory Tech., Vol. 31, No. 8, 674-678, Aug. 1983. doi:10.1109/TMTT.1983.1131568
6. Paco, P. D., J. Verdu, O. Menendez, and E. Corrales, "Branch-line coupler based on edge-coupled parallel lines with improved balanced response," IEEE Trans. Microw. Theory Tech., Vol. 56, No. 12, 2936-2941, Dec. 2008. doi:10.1109/TMTT.2008.2007191
7. Kim, J.-S. and K.-B. Kong, "Compact branch-line coupler for harmonic suppression," Progress In Electromagnetics Research C, Vol. 16, 233-239, 2010. doi:10.2528/PIERC10083011
8. Li, B., X. Wu, and W. Wu, "A miniaturized branch-line coupler with wideband harmonics suppression," Progress In Electromagnetics Research Letters, Vol. 17, 181-189, 2010. doi:10.2528/PIERL10082602
9. Shum, K. M., Q. Xue, and C. H. Chan, "A novel microstrip ring hybrid incorporating a PBG cell," IEEE Microw. Wireless Compon. Lett., Vol. 11, No. 6, 258-260, Jun. 2001. doi:10.1109/7260.928931
10. Shie, C.-I., J.-C. Cheng, S.-C. Chou, and Y.-C. Chiang, "Design of cmos quadrature vco using on-chip trans-directional couplers," Progress In Electromagnetics Research, Vol. 106, 91-106, 2010. doi:10.2528/PIER10053002
11. Andrews, D. P. and C. S. Aitchison, "Wide-band lumped-element quadrature 3-dB couplers in microstrip," IEEE Trans. Microw. Theory Tech., Vol. 48, No. 12, 2424-2431, Dec. 2000. doi:10.1109/22.898993
12. Sun, S. and L. Zhu, "Multiple-resonator-based bandpass filters," IEEE Microwave Magazine, Vol. 10, No. 2, 88-98, Apr. 2009. doi:10.1109/MMM.2008.931673
13. Wu, Y.-L., C. Liao, and X.-Z. Xiong, "A dual-wideband bandpass filter based on e-shaped microstrip SIR with improved upper-stopband performance," Progress In Electromagnetics Research, Vol. 108, 141-153, 2010. doi:10.2528/PIER10071802
14. Wu, H.-W., S.-K. Liu, M.-H. Weng, and C.-H. Hung, "Compact microstrip bandpass filter with multispurious suppression," Progress In Electromagnetics Research, Vol. 107, 21-30, 2010. doi:10.2528/PIER10061601
15. Dai, G. and M. Xia, "Novel miniaturized bandpass filters using spiral-shaped resonators and window feed structures," Progress In Electromagnetics Research, Vol. 100, 235-243, 2010. doi:10.2528/PIER09120401
16. Yang, T., M. Tamura, and T. Itoh, "Compact hybrid resonator with series and shunt resonances used in miniaturized filters and balun filters," IEEE Trans. Microw. Theory Tech., Vol. 58, No. 2, 390-402, Feb. 2010. doi:10.1109/TMTT.2009.2038662
17. Yeung, L. K. and K.-L. Wu, "A dual-band coupled-line balun filter," IEEE Trans. Microw. Theory Tech., Vol. 55, No. 11, 2406-2411, Nov. 2007. doi:10.1109/TMTT.2007.907402
18. Zheng, S. Y., W. S. Chan, and K. F. Man, "Multi-function patch element," Progress In Electromagnetics Research, Vol. 109, 159-174, 2010. doi:10.2528/PIER10081801
19. Yeung, L. K. and K.-L. Wu, "An integrated RF balanced-filter with enhanced rejection characteristics," IEEE MTT-S Int. Microw. Symp. Dig., 713-716, 2005. doi:10.1109/MWSYM.2005.1516708
20. Yeung, L. K. and K.-L. Wu, "An LTCC balanced-to-unbalanced extracted-pole bandpass filter with complex load," IEEE Trans. Microw. Theory Tech., Vol. 54, No. 4, 1512-1518, Apr. 2006. doi:10.1109/TMTT.2006.871363
21. Watkins, J. and S. Uysal, "Novel microstrip directional band-pass/band-stop couplers and filters," IEEE MTT-S Int. Microw. Symp. Dig., 411-414, 1990.
22. Uysal, S. and J. Watkins, "Novel microstrip multifunction directional couplers and filters for microwave and millimeter-wave applications," IEEE Trans. Microw. Theory Tech., Vol. 39, No. 6, 977-985, Jun. 1991. doi:10.1109/22.81667
23. Chen, D. and C.-H. Cheng, "A novel compact ultra-wideband (UWB) wide slot antenna with via holes," Progress In Electromagnetics Research, Vol. 94, 343-349, 2009. doi:10.2528/PIER09062306
24. Kim, H., B. Lee, and M.-J. Park, "Dual-band branch-line coupler with port extensions," IEEE Trans. Microw. Theory Tech., Vol. 58, No. 3, 651-655, Mar. 2010. doi:10.1109/TMTT.2010.2040342
25. Park, M.-J., "Dual-band wilkinson divider with coupled output port extensions," IEEE Trans. Microw. Theory Tech., Vol. 57, No. 9, 2232-2237, Sep. 2009. doi:10.1109/TMTT.2009.2027169
26. Kawai, T., H. Taniguchi, I. Ohta, and A. Enokihara, "Broadband branch-line coupler with arbitrary power split ratio utilizing mircrostrip series stubs," Proc. 40th Microw. Conf., 1170-1173, Sep. 2010.
27. Ashforth, J. V., "Design equations to realize a broadband hybrid ring or a two-branch guide coupler of any coupling coe±cient," Electron. Lett., Vol. 24, No. 20, 1276-1277, Sep. 1988. doi:10.1049/el:19880869
28. Johnson, A. K. and G. I. Zysman, "Coupled transmission line networks in an inhomogeneous dielectric medium," IEEE Trans. Microw. Theory Tech., Vol. 17, No. 10, 753-759, Oct. 1969.
29. Tripathi, V. K., "Asymmetric coupled transmission lines in an inhomogeneous medium," IEEE Trans. Microw. Theory Tech., Vol. 23, No. 9, 734-739, Sep. 1975. doi:10.1109/TMTT.1975.1128665