1. Ali, A. A. M., N. J. G. Fonseca, F. Coccetti, and H. Aubert, "Design and implementation of two-layer compact wideband Butler matrices in SIW technology for Ku-band applications," IEEE Trans. Anten. Progp., Vol. 59, No. 2, 503-512, 2011.
doi:10.1109/TAP.2010.2093499
2. Nedil, M., T. A. Denidni, and L. Talbi, "Novel Butler matrix using CPW multilayer technology," IEEE Trans. Microw. Theory Tech., Vol. 54, No. 1, 499-507, 2006.
doi:10.1109/TMTT.2005.860490
3. Gruszczynski, S. and K. Wincza, "Broadband 4x4 Butler matrices as a connection of symmetrical multisection coupled-line 3-dB directional couplers and phase correction networks," IEEE Trans. Microw. Theory Tech., Vol. 57, No. 1, 1-9, 2009.
doi:10.1109/TMTT.2008.2009081
4. Djerafi, T., N. J. G. Fonseca, and K. Wu, "Design and implementation of a planar 4x4 Butler matrix in SIW technology for wideband applications," Proceedings of the 40th European Microwave Conference, 910-913, 2010.
5. Zheng, S., W. S. Chan, S. H. Leung, and Q. Xue, "Broadband Butler matrix with flat coupling," Electr. Lett., Vol. 43, No. 10, 576-577, 2007.
doi:10.1049/el:20070274
6. He, J., B. Z. Wang, Q. Q. He, Y. X. Xing, and Z. L. Yin, "Wideband X-band microstrip Butler matrix," Progress In Electromagnetics Research, Vol. 74, 131-140, 2007.
doi:10.2528/PIER07042302
7. Vogel, R. W., "Analysis and design of lumped- and lumped-distributed element directional couplers for MIC and MMIC applications," IEEE Trans. Microw. Theory Tech., Vol. 40, No. 2, 253-262, 1992.
doi:10.1109/22.120097
8. Chun, Y. H. and J. S. Hong, "Design of a compact broad-band branchline hybrid," IEEE MTT-S Int. Microw. Symp. Dig., 997-1000, Long Beach, CA, 2005.
9. Chun, Y. H. and J. S. Hong, "Compact wide-band branch-line hybrids," IEEE Trans. Microw. Theory Tech., Vol. 54, No. 2, 704-709, 2006.
doi:10.1109/TMTT.2005.862657
10. Schiffman, B. M., "A new class of broad-band microwave 90-degree phase shifters," IRE Trans. Microw. Theory Tech., 232-237, 1958.
doi:10.1109/TMTT.1958.1124543
11. Quirartc, J. L. R. and J. P. Starski, "Synthesis of Schiffman phase shifters," IEEE Trans. Microw. Theory Tech., Vol. 39, No. 11, 1885-1889, 1991.
doi:10.1109/22.97492
12. Muracuchi, 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, 1983.
doi:10.1109/TMTT.1983.1131568
13. Jafari, E., F. Hodjatkashani, and R. Rezaiesarlak, "A broadband quadrature hybrid using improved wideband Schiffman phase shifter," Progress In Electromagnetics Research C, Vol. 11, 229-236, 2009.
doi:10.2528/PIERC09112101
14. Zhang, Z., Y. C. Jiao, S. F. Cao, X. M. Wang, and F. S. Zhang, "Modified broadband Schiffman phase shifter using dentate microstrip and patterned ground plane," Progress In Electromagnetics Research Letters, Vol. 24, 9-16, 2011.