Md Jizat, Noorlindawaty, et al. “Multibeam Array Antenna With Compact Size Butler Matrix for Millimeter-Wave Application”. International Journal of Integrated Engineering, vol. 15, no. 3, Aug. 2023, pp. 140-52, https://penerbit.uthm.edu.my/ojs/index.php/ijie/article/view/12883.