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

A 4 × 4 Butler Matrix (BM) without phase shifter is proposed to provide bandwidth enhancement and size reduction by removing a conventional 0 dB/90° crossover, two 0° phase shifters and two 45° phase shifters. Two proposed 3 dB/45° patch couplers replace the combination of two conventional 3 dB/90° branch-line couplers and two 45° phase shifters, whilst a modified 0 dB/0° crossover removes two 0° 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°, −135°, +135° and −45° of output phase differences with 1.8° 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°, −50°, +50° and −15° are developed by integrating the proposed BM with inset feeding patch antennas. The proposed BM is miniaturized by 51.56%, whilst the bandwidth performance is enhanced by 9.7% compared to the conventional BM. Hence, this compact BM is a promising candidate for the fifth generation (5G) communication system.