A halo antenna, also known as a halo, is a specific type of antenna that consists of a center-fed dipole antenna. The dipole, which has a length equal to half the wavelength, is bent into a circular shape with a break directly opposite the feed point. The ends of the dipole are positioned close to each other but do not touch. By modifying the cross-section of the ends, an air capacitor can be formed. The spacing of this capacitor is adjusted to fine-tune the resonant frequency of the antenna.
Typically, the halo antenna is mounted horizontally. In this configuration, it exhibits an approximate omnidirectional radiation pattern, meaning it radiates equally in all directions around the horizontal plane. Moreover, the radiation from this antenna is horizontally polarized, which means that the electric field of the radiated signals is primarily oriented in a horizontal direction.
Overall, the halo antenna's unique design and characteristics make it well-suited for applications where omnidirectional coverage and horizontal polarization are desired.