File:Monopole and image antenna.svg

English: Diagram showing why a monopole antenna has the same radiation pattern as a dipole antenna, with twice the radiated power. When a monopole antenna, (a) is mounted over a perfectly conducting ground plane such as the Earth, the radio waves can reach a given point P by two paths, either propagating directly in a straight line to P, or reaching P after first reflecting from the plane (blue) it has the same radiation pattern as it would if the ground plane were replaced with a virtual image antenna (b) located under the ground. The monopole and its image together are equivalent to a dipole antenna driven with a voltage twice as large as the monopole's (2V) but with the same element currents as the monopole. So the gain of the monopole will be twice that of the dipole