In radio telecommunications, an omnidirectional antenna is a type of antenna that radiates radio waves at a uniform power in all directions on a plane, with decreasing radiating power in relation to the angle above or below the plane, going down to zero on the antenna axis. The radiated power reaches its maximum in the horizontal directions, falling to zero directly above and below the antenna. The radiation diagram has toroidal form and is sometimes described as "doughnut-shaped". Note that it is different from an isotropic antenna, abstraction of an ideal antenna that radiates the same power in all directions with a spherical radiation diagram. Omnidirectional antennas positioned with the vertical axis are often used as non-directional antennas relative to the Earth's surface, as they radiate evenly in all horizontal directions and the radiated power drops as the radiance increases. causing little energy to be dispersed to the sky or to the ground. Omnidirectional antennas are often used by radio stations and mobile devices that use radio such as mobile phones, FM radios, walkie-talkies, wireless networks, cordless phones, GPS as well as base radio stations that communicate with radios police and radio-taxi and communications between planes.