1. Liu, Q., Y. Liu, Y. Wu, S. Li, C. Yu, and M. Su, "Broadband substrate integrated coaxial line to CBCPW transition for rat-race couplers and dual-band couplers design," Progress In Electromagnetics Research C, Vol. 35, 147-159, 2013.
doi:10.2528/PIERC12111902
2. He, Q., J. Shen, Q. Liu, J. Li, and L. Liang, "A simplified dual-band rat-race hybrid for arbitrary power division ratio with only single shunt stub," Journal of Electromagnetic Waves and Applications, Vol. 27, No. 16, 2101-2109, 2013.
doi:10.1080/09205071.2013.832396
3. Gu, J. Z. and X. W. Sun, "Miniaturization and harmonic suppression rat-race coupler using C-SCMRC with distributive equivalent circuit," IEEE Microw. Wirel. Compon. Lett., Vol. 15, No. 12, 880-882, 2005.
doi:10.1109/LMWC.2005.859980
4. Mondal, P. and A. Chakrabarty, "Design of miniaturised branch-line and rat-race hybrid couplers with harmonics suppression," IET Microw. Antennas Propag., Vol. 3, No. 1, 109-116, 2009.
doi:10.1049/iet-map:20070202
5. Lai, C. H. and T. G.Ma, "Miniaturised rat-race coupler with second and third harmonic suppression using synthesised transmission lines," Electron. Lett., Vol. 49, No. 22, 1394-1396, 2013.
doi:10.1049/el.2013.2975
6. Kuo, J. T., J. S. Wu, and Y. C. Chiou, "Miniaturized rat race coupler with suppression of spurious passband," IEEE Microw. Wirel. Compon. Lett., Vol. 17, No. 1, 46-48, 2007.
doi:10.1109/LMWC.2006.887254
7. Tyrrell, W.-A., "Hybrid circuits for microwaves," Proc. IRE, Vol. 35, No. 11, 1294-1306, 1947.
doi:10.1109/JRPROC.1947.233572
8. Reed, J. and G.-J. Wheeler, "A method of analysis of symmetrical four-port networks," IRE Trans. Microw. Theory Tech., Vol. 4, No. 4, 246-252, 1956.
doi:10.1109/TMTT.1956.1125071
9. Kuo, J.-T. and C.-H. Tsai, "Generalized synthesis of rat race ring coupler and its application to circuit miniaturization," Progress In Electromagnetics Research, Vol. 108, 51-64, 2010.
doi:10.2528/PIER10071705
10. Rathore, J., S. Aditya, and R. S. C. Dutta, "A general analysis and new designs for the hybrid-ring directional coupler," Indian J. Technol., Vol. 31, 827-830, 1993.
11. He, Q., Y. A. Liu, S. L. Li, M. Su, and Y. L.Wu, "A novel 180 degrees rat-race hybrid with arbitrary power division for complex impedances," Journal of Electromagnetic Waves and Applications, Vol. 27, No. 3, 318-329, 2013.
doi:10.1080/09205071.2013.744713
12. Lin, F., Q.-X. Chu, and S.-W. Wong, "Compact broadband microstrip rat-race couplers using microstrip/slotline phase inverters for arbitrary power-dividing ratios," Journal of Electromagnetic Waves and Applications, Vol. 26, No. 17–18, 2358-2364, 2012.
doi:10.1080/09205071.2012.734437
13. Kim, D. I. and G. S. Yang, "Design of new hybrid-ring directional coupler using λ/8 or λ/6 sections," IEEE Trans. Microw. Theory Tech., Vol. 39, No. 10, 1779-1783, 1991.
doi:10.1109/22.88553
14. Ho, K. L. and P.-L. Chi, "Miniaturized and large-division-ratio ring coupler using novel transmission-line elements," IEEE Microw. Wirel. Compon. Lett., Vol. 24, No. 1, 35-37, 2014.
doi:10.1109/LMWC.2013.2288261
15. Velidi, V. K., M. K. Mandal, and A. Bhattacharya, "Uniplanar harmonic suppressed compact rat-race couplers," Microw. Optical Techn. Lett., Vol. 50, No. 11, 2812-2814, 2008.
doi:10.1002/mop.23840
16. Xu, H.-X., G.-M. Wang, and K. Lu, "Microstrip rat-race couplers," IEEE Microw. Magazine, Vol. 12, No. 4, 117-129, 2011.
doi:10.1109/MMM.2011.940600
17. Tu, W. H. and K. Chang, "Compact second harmonic-suppressed bandstop and bandpass filters using open stubs," IEEE Trans. Microw. Theory Tech., Vol. 54, No. 6, 2497-2502, 2006.
doi:10.1109/TMTT.2006.875802
18. Liu, G.-Q., L.-S. Wu, and W.-Y. Yin, "A compact microstrip rat-race coupler with modified lange and t-shaped arms," Progress In Electromagnetics Research, Vol. 115, 509-523, 2011.
doi:10.2528/PIER11032003
19. Tseng, C. H. and C. L. Chang, "A rigorous design methodology for compact planar branch-line and rat-race couplers with asymmetrical T-structures," IEEE Trans. Microw. Theory Tech., Vol. 60, No. 7, 2085-2092, 2012.
doi:10.1109/TMTT.2012.2195019