In
radio communication, an
omnidirectional antenna is a class of
antenna which radiates
radio wave power uniformly in all directions in one plane, with the radiated power decreasing with elevation angle above or below the plane, dropping to zero on the antenna's axis. This
radiation pattern is often described as "doughnut shaped". Note that this is different from an
isotropic antenna, which radiates equal power in
all directions and has a "spherical" radiation pattern. Omnidirectional antennas oriented vertically are widely used for nondirectional antennas on the surface of the Earth because they radiate equally in all horizontal directions, while the power radiated drops off with elevation angle so little radio energy is aimed into the sky or down toward the earth and wasted. Omnidirectional antennas are widely used for
radio broadcasting antennas, and in mobile devices that use radio such as
cell phones,
FM radios,
walkie-talkies,
wireless computer networks,
cordless phones,
GPS as well as for base stations that communicate with mobile radios, such as police and taxi dispatchers and aircraft communications.