Bandwidth Improvement of Center-Fed Series Antenna Array Targeting for Base Stations in Offshore 5G Communications

A 1 × 12 center-fed series antenna array, with a novel probe feeding structure to broaden the bandwidth, is designed for 5G base stations deployed in the land for offshore maritime communications. The improvement of the bandwidth is achieved through a combination of folding and replacing the center feed line to a lower layer away from patch radiators. By moving the center feed line to the lower layer beneath radiators, serious mutual-coupling and corresponding parasitic effect between the feed and radiators are reduced, facilitating better transmission and also resulting in better matching to the 50-Ω coaxial probe. Moreover, a vertically folded-U structure is proposed to be inserted in part of the feed line, to provide a section of a high impedance microstrip line and further broaden the impedance bandwidth. A simulation study is performed on the geometry of the center feed line to investigate how the antenna performance can be controlled. The antenna array design procedure is outlined and a prototype with over 20% bandwidth, which can fully cover the 4.8-4.99 GHz 5G spectrum band, is fabricated and measured for impedance matching, radiation pattern, and broadside gain. For both S-parameter and far-field results, good correspondence is achieved between simulation and measurement. The proposed series-fed antenna array with coaxial feed is very suitable to be deployed in base stations with 1-D beam steering capability.