An omnidirectional antenna is one of two types of commonly available antennas for wireless devices.
The omnidirectional antenna is normally made up of the shape of a cylinder.
It usually tries to propagate a signal equally in all directions from the cylinder, resulting in a donut shape pattern that extended further in the H-plane rather than the E-plane.
An omnidirectional antenna is normally suited for providing coverage in a large area with the antenna located centrally.
There is low gain in an omnidirectional antenna since it spreads the signal so widely over a area.
A common type of omnidirectional antenna is the dipole antenna. A dipole antenna can be folded up and down depending on the mounting orientation of the wireless access point.
The dipole antenna has two separate wires that radiate a radio frequency signal when an alternating current is applied to them.
A dipole antenna has a gain of around +2 to +5 dBi
Many access points such as Cisco access points have integrated antennas inside of the devices shell. Integrated antennas normally have a gain of +2dBi in the 2.4Ghz band and +5dBi in the 5Ghz band.