Directive Millimeter-Wave End-Fire Diplexing Antenna for IoT Applications

Millions of passengers use high-speed trains (HSTs) daily, in the world. The roofs of HSTs can be equipped with a variety of transmitting and receiving antennas to accommodate high-data-rate Internet services with reliable radio access for passengers. The design of commercial antenna systems is a compromise between cost, size, manufacturability, and performance. This article proposes a new, compact, and low-cost two-port millimeter-wave diplexing directive end-fire antenna, which is designed, fabricated, and tested. The proposed antenna is made of a tapered slot antenna and a diplexing structure based on transitions in stacked printed circuit boards (PCBs). The ports of the antenna cover the frequency band 25.9–32.4 GHz (6.5 GHz) and 34.6–37.1 GHz (2.5 GHz). In all operating frequency bands, measured isolation between input ports exceeds 24 dB. Furthermore, symmetric directive end-fire radiation patterns are obtained experimentally, with low sidelobe level and low front-to-back ratio. All these features make the proposed diplexing antenna suitable for high-speed railway wireless networks.