Review of Antennas for Railway Communications

This paper presents a review of the state-of-the-art antennas for the railway communications. There are various aspects that one should consider when designing an antenna, such as antenna size and directivity. While size constraints on railway antennas are not as critical as for mobile consumer counterparts, a radome structure is required to cover the antenna to minimize the aerodynamic resistance antenna. This paper reviews aerodynamic simulations to account for the drag coefficient of the antenna. In a low-frequency band (<5 GHz), railway antennas used to be omnidirectional in the horizontal plane. As the communication scheme advances toward 5G technology, high directivity is required for the railway antenna to compensate for the high path loss at high-frequency bands, i.e., 28-GHz band. We review recent studies of railway antennas over various frequency bands, such as LTE-R, LTE, and the lower and upper 5G bands. To accommodate multiple frequency bands with a single antenna, along with the aerodynamic radome cover, design techniques allowing multiple frequency bands are reviewed in this paper.