Effects of Closed-Loop Devices on Omnidirectional Beam Patterns Radiated from WAVE Monopole Antennas

This study investigates the influence of closed-loop devices on omnidirectional beam patterns radiated from a Wireless Access for Vehicle Environment (WAVE) monopole antenna for facilitating communication stability in Vehicle-to-Vehicle and Vehicle-to-Everything technology. Single, dual, and quadruple closed-loop devices were introduced into the monopole antenna, and their surface current density and radiation beam patterns were analyzed by using the high-frequency structure simulator (HFSS) and computer simulation technology (CST) programs. As the closed-loop devices reflected the signal radiated from the antenna, the distribution of the surface current was concentrated around the monopole due to the creation of a closed-loop surface current path, which increased the gain value. The average gain was considerably increased by introducing closed-loop devices. The proposed antenna has an average gain of 1.57 dBi and a peak gain of 6.29 dBi at the operating frequency. Furthermore, omnidirectional beam patterns with a beam width of 359° were obtained by introducing four closed-loop devices into the monopole antenna, which eliminated nearly all null points in the frequency range of 5.85–5.925 GHz.