English: Diagram of a quarter-wave monopole antenna and its image (dotted line) reflected by a ground plane. Label in english. When a monopole antenna is mounted above a ground plane such as the Earth, the radio waves emitted downwards by the antenna reflect off the ground plane. The radiation pattern of the antenna is the sum of the direct waves and the reflected waves, which seem to come from an image antenna below the ground. The real antenna and its image form a dipole antenna, so the radiation pattern of a monopole antenna is the top half of a dipole radiation pattern.