A Wideband and Small Diameter Halo Antenna with Four Parasitic Elements

In recently, many vertically polarized antennas are mainly used for various mobile communications to save installation space. Therefore, a horizontally polarized antenna is desirable for polarization diversity to avoid interference. In addition, an omnidirectional radiation pattern is required to enable smooth transmission and reception even if the posture of the mobile changes. In this paper, we focus on the Halo antenna, which is a type of horizontally polarized antenna with an omnidirectional radiation pattern in the horizontal plane [1] . The Halo antenna is a folded dipole antenna that is bent into a cylindrical shape, and the input impedance of the Halo antenna can be adjusted by changing the gap width and the height of the antenna. However, the Halo antenna has a narrow band characteristic, and in order to reduce the lowest operating frequency of the Halo antenna while maintaining the relative bandwidth, it is necessary to increase the diameter of the antenna. Therefore, it has been reported by loading two parasitic elements in the vertical direction of the Halo antenna, the diameter of the antenna is not changed and the relative bandwidth is expanded [2] .