What are the radials on an antenna?

Radials on an antenna serve as an artificial "ground" for many vertically polarized antennas. They consist of wire, mesh or metal rods that are laid out radially and horizontally from the base of the antenna. Their function is to form the opposite side for the RF signal. Without radials, the ground or ground plane would be missing, which could lead to impaired radiation characteristics and very poor antenna efficiency.