Beam-Switching Antenna Array Using Rotman Lens for Railway Communication at 28 GHz

In this paper, a multibeam antenna without a phase shifter is designed for railway communications in the upper 5G band (28 GHz). Railway turning angles can reach up to -20° to 20° depending on line geometry and train speed. Based on the curvature of railway tracks in realistic scenarios, the required beam deflection range spans -30° to 30°. This limited beam deflection range makes the Rotman lens a suitable replacement for phase shifters in beam steering, thereby significantly reducing system cost. Depending on the choice of antenna element, the antenna can create either linear or circular polarization. The measurement results demonstrate that the linearly and circularly polarized antennas achieved maximum directivities of 10.8 dBi and 11.2 dBi, respectively. The antenna bandwidth under linear (circular) polarization reached 2 GHz (1.8 GHz), which is sufficient to support the high data-rate requirements of the 5G communications. In addition, the antenna size was minimized to fit into a shark-fin cover mounted on the vehicle.