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.