Array Antenna Feeding Network Design for 5G MIMO Applications

Abstract

Emerging smart antenna systems require different beam patterns of multiple antennas. Although adjustable phase shifters are mostly used in continuous beam systems, the Butler matrix is used in switching beam systems due to its low cost and easy fabrication. In this study, an antenna-array-feeding circuit based on the Butler matrix that can be used for Multiple Input Multiple Output applications is designed for 5G new radio. With the proposed switching system, the control of four beams can be achieved. The Butler circuit, designed to cover the 3.5-4.2 GHz 5G band, has a low complexity and is capable of meeting the need for high data throughput. A simulation of the circuit and circuit sub elements designed using a 0.508-mm-thick substrate material is performed using the Computer Simulation Technology Microwave Studio computer aided design tool. Furthermore, a prototype of the Butler circuit is fabricated, and the amplitude and phase variations at the output ports are measured. An average transmission loss of the feed circuit is measured as 1.5 dB, and when the length of the Phase Shifter in the circuit is set to lambda/8, with a four element linear array added to the output of the Butler circuit, the main beam is steered to +/- 150 and +/- 350 having maximum gain in the 6.39-8.77 dBi range.