Omnidirectional or omnidirectional antennas are antennas whose radiation pattern is 360 degrees in the horizontal and is the same in all directions. A typical omnidirectional antenna is a rod antenna tuned to `lamda/2`. It has the maximum radiation at an angle of 90 degrees to the antenna axis and all around in the horizontal with the same field strength. Other omnidirectional antennas are the slot antenna, discone antenna and big-wheel antenna.
In the vertical direction, the radiation characteristic of an omnidirectional antenna is lobe-shaped with a small beam angle. This can be only a few degrees, up to about 15 °. By reducing the vertical beam angle, the transmitted energy is concentrated on the narrower radiation lobe, which results in a higher antenna gain.
Omnidirectional omnidirectional antennas are ideal for indoor use in WLANs, where they can be connected to access points( AP) or to WLAN routers to cover all stations on the same level, floor, hall or hall. Stations higher or lower down are not adequately supplied, which is due to the vertical radiation characteristics.
When used in WLANs, the electromagnetic radiation of the microwaves can penetrate high- frequency permeable partition walls made of wood or plaster. With increasing antenna gain, the orientation in the horizontal plane is quite decisive for the reception conditions. The antenna gain of lambda/2 omnidirectional antennas is typically between 3 dBi and 5 dBi. For other omnidirectional antennas in the ISM band between 2.4 GHz and 2.5 GHz, the antenna gain is between 2 dBi and 15 dBi.