Design and characterization of a compact single-layer multibeam array antenna using an 8×8 Butler matrix for 5G base station applications

Abstract

A multibeam array antenna employing a Butler matrix is a promising solution for fifth generation (5G) basestations. Due to inaccurate phase differences between output ports in the Butler matrix, the radiation characteristicscould show incorrect main beam directions. In addition, the literature has also reported the issue of high amplitudeimbalance in the Butler matrix. This paper presents a single-layer multibeam array antenna fed by an 8×8 Butlermatrix operating at 28 GHz for 5G base station applications—a more cost-effective solution for large-scale production.The Butler matrix consists of twelve quadrature hybrids, sixteen crossovers, and eight phase shifters. This circuit wasintegrated with eight antenna elements at the output ports of the Butler matrix. The proposed multibeam array antennawas fabricated using a low dielectric constant and a low loss tangent substrate. The dimensions of the multibeam arrayantenna were 88×106×0.254 mm3. The Butler matrix achieved low insertion losses and low phase error with averagevalues of 2.5 dB and less than ±10◦at 28 GHz, respectively. The measured return losses were less than −10 dB at28 GHz. The measured radiation patterns were obtained and eight main beams were pointed at ±6◦, ±18◦, ±30◦, and±44◦ with measured gains between 9 dBi and 14 dBi.