Miniaturized 4 x 4 switched-beam Butler Matrix with bandwidth enhancement for 5G communication system

A 4 x 4 Butler Matrix (BM) without phase shifter is proposed to provide bandwidth enhancement and size reduction by removing a conventional 0 dB/90 degrees crossover, two 0 degrees phase shif-ters and two 45 degrees phase shifters. Two proposed 3 dB/45 degrees patch couplers replace the combination of two conventional 3 dB/90 degrees branch-line couplers and two 45 degrees phase shifters, whilst a modified 0 dB/0 degrees crossover removes two 0 degrees phase shifters from the conventional BM. The-10 dB fractional bandwidths of reflection coefficients and isolations for the proposed BM are 18.46% in simulation and measurement. The-6 dB +/- 1.5 dB average transmission coefficient and +45 degrees,-135 degrees, +135 degrees and-45 degrees of output phase differences with 1.8 degrees average phase imbalance are accomplished at 6.5 GHz. The simulated and measured scattering parameters (S-parameters) and phase differences are in close compliance with each other. Four switched-beams pointed at +15 degrees,-50 degrees, +50 degrees and-15 degrees are developed by integrating the proposed BM with inset feeding patch antennas. The pro-posed BM is miniaturized by 51.56%, whilst the bandwidth performance is enhanced by 9.7% com-pared to the conventional BM. Hence, this compact BM is a promising candidate for the fifth generation (5G) communication system.(c) 2022 THE AUTHORS. Published by Elsevier BV on behalf of Faculty of Engineering, Alexandria University This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/ licenses/by-nc-nd/4.0/).