Omnidirectional antenna

An omnidirectional antenna is a class of antennae that receives signals equally from all directions and can send signals equally in each direction. For an omnidirectional antenna, a signal is emitted or received in a 360-degree plane from the antenna locus to cover a certain area. In this case, the signal is considered unfocused, with a relatively smaller distance covered relative to the distance covered by a unidirectional antenna. Further, depending on the reach of the antenna, there can be areas of poor coverage due to the emission patterns, including under the antenna itself.

An omnidirectional antenna does not perform equally well in all possible directions in three-dimensional space. Some suggest a true omnidirectional antenna can only exist in theory but can be approached in practice. These are sometimes called isotropic antennae or isotropic radiators. Further, depending on the placement of the antenna, obstructions and nearby conducting objects can distort the radiation and reception pattern.

Overall, the advantages offered by an omnidirectional antenna are the ability to send a signal in all directions and no need to adjust the antenna if the receiver moves to a new location. It also means the receiver does not need to know where to point the omnidirectional antenna or where a local tower is located and can be useful when there are multiple towers in an area, which the omnidirectional antenna can receive. The disadvantage of omnidirectional antenna design is the same as the advantage—as it points in all directions, rather than focusing its power in one direction, it does not emit as strong a signal as a unidirectional antenna.

Omnidirectional antennae have specific use cases, in which covering a wide area is preferred over covering a single direction. Use cases include base stations for communications, such as radio stations, emergency communications, or other radio-based communications, such as walkie-talkies. They are used in Wi-Fi modems, both to send signals to devices and for devices—such as cell phones, mobile computers, or stationary computers—to receive and resend the signal and for developing indoor and outdoor Wi-Fi hotspots. They are used to receive GPS signals in handsets from space-based global positioning satellites (which use unidirectional antennae). And they can be used for various Internet of Things (IoT) and smart city or vehicle implementations, where covering a wide area is necessary, rather than a point-to-point style system.