1. Kim, S., S. Yoon, Y. Lee, and H. Shin, "A miniaturized Butler matrix based switched, beamforming antenna system in a two-layer hybrid stackup substrate for 5G applications," Electronics, Vol. 8, 1232, 2019, doi: 10.3390/electronics8111232.
doi:10.3390/electronics8111232
2. Han, K., W. Li, and Y. Liu, "Flexible phase difference of 4x4 Butler matrix without phase-shifters and crossovers," International Journal of Antennas and Propagation, Vol. 2019, Article ID 4703161, 7 pages, 2019, https://doi.org/10.1155/2019/4703161.
3. Hao, Z. C., W. Hong, J. X. Chen, H. X. Zhou, and K. Wu, "Single-layer substrate integrated waveguide directional couplers," IEE Proc. Microwave Antennas Propag., Vol. 153, No. 5, 426-431, Oct. 2006.
doi:10.1049/ip-map:20050171
4. Babale, S. A., S. K. Abdul Rahim, O. A. Barro, M. Himdi, and M. Khalily, "Single layered 4 x 4 Butler matrix without phase-shifters and crossovers," IEEE Access, Vol. 6, 77289-77298, 2018.
doi:10.1109/ACCESS.2018.2881605
5. Wang, Y., K. Ma, N. Yan, and L. Li, "Design of broad band SIW couplers with 45◦ and 90◦ phase difference," Proceedings of iWEM 2014, Sapporo, Japan, 2014.
6. Liu, H., X. Li, Y. Guo, S.-J. Fang, and Z. Wang, "Design of filtering coupled-line trans-directional coupler with broadband bandpass response," Progress In Electromagnetics Research M, Vol. 100, 163-173, 2021.
doi:10.2528/PIERM20110405
7. Muquaddar, A., K. K. Sharma, and R. P. Yadav, "Design and analysis of a stub-less capacitive loaded branch line coupler with improved bandwidth performance," Progress In Electromagnetics Research M, Vol. 95, 105-114, 2020.
8. Liu, H., X. Wang, T. Zhang, S.-J. Fang, and Z. Wang, "Design of full-360◦ reflection-type phase shifter using trans-directional coupler with multi-resonance loads," Progress In Electromagnetics Research Letters, Vol. 101, 63-70, 2021.
doi:10.2528/PIERL21091802
9. "Microwave power dividers and couplers tutorial," http://www.markimicrowave.com/menus/appno- tes/Microwave Power Dividers and Couplers Primer.pdf, Marki Microwave, accessed Jan. 2012.
10. Pozar, D., Microwave Engineering, 3rd Edition, Wiley, New York, 2005.
11., https://www.keysight.com/zz/en/home.html, Jan. 2022.
12. Moubadir, M., H. Aziz, N. A. Touhami, and A. Mohamed, "A miniaturized branch-line hybrid coupler microstrip for long term evolution applications," Procedia Manufacturing, Vol. 22, 491-497, 2018.
doi:10.1016/j.promfg.2018.03.075
13. Dinh, T. A. N., L. H. Duc, D. B. Gia, and D. Dancila, "A design of wideband high-power 3-dB quadrature coupler using defected ground structure for status data transmitting system," Bulletin of Electrical Engineering and Informatics, Vol. 9, No. 1, Feb. 2020.
doi:10.11591/eei.v9i1.1699