This article presents the design of a three-port diversity antenna capable of producing three-directional radiation pattern for vehicular communications. The proposed antenna consists of three uncorrelated Vivaldi antennas that are interconnected and developed on a single printed circuit board. Unlike many other antennas reported for the vehicular environment, the proposed antenna offers ultra-wideband characteristics with end-fire radiation pattern leading to high realized antenna gain. The integrated antenna has a footprint of 65 × 40 × 1.6 mm3 and offers 6 GHz impedance bandwidth extending from 5 to 11 GHz. The port-to-port isolation is greater than 20 dB within the operating bandwidth. Furthermore, the diversity performance of the proposed three-port antenna system is evaluated and presented. The calculated envelope correlation coefficient, diversity gain, and mean effective gain are well above the minimum requirement. The prototype antenna is fabricated and the experimental results are presented. © 2019 Wiley Periodicals, Inc.