An omni-directional antenna is designed to provide a 360 degree radiation pattern . This type of antenna is used when coverage in all directions from the antenna is required.

Omni-directional antennas come in many different styles and shapes. Most operated in the 2.4 GHz ranges, whereas a few operate in the 5 GHz range. Omni-directional antennas include dipoles, mast mount, pillar, and patch antennas . The standard 2.14 dBi "Rubber Duck" is the most commonly used omni-directional antenna.

In a perfect world, all the omni-directional antennas would radiate perfectly in all directions. Unfortunately, this is not the case. Notice the radiation pattern of each antenna as they are presented in this module. The radiation patterns will be shown as a horizontal (H-plane) radiation pattern, an Elevation (E-plane) radiation pattern, or both. Elevation plane radiation is sometimes called vertical plane radiation as well.

The H-plane is also referred to as the Azimuth Plane Pattern. This can be envisioned by looking at a top view of the antenna, looking down . Notice the green area can be viewed as a tabletop, floor, or ground below the antenna. All of the H-plane omni-directional patterns are virtually the same, which is a 360 degree pattern . However, keep in mind that the gain determines the distance of the radiation. For instance, the 12dBi mast mount will reach much further than the 2.2 dBi dipole.

The E-plane can be envisioned as the antenna perpendicular to the ground . The E-Plane radiation patterns can be significantly different between omni-directional antennas. Pay careful attention to these differences. Knowing the antenna radiation patterns are very important when locating antennas during the test and installation phase.

Everything about antenna choice involves a tradeoff. If maximum range is desired, coverage must be traded. Do not forget that coverage is more than just horizontal. There is a vertical aspect also. Most omni-directional antennas trade vertical coverage for additional range. Antenna coverage can be likened to a balloon. Pressing on the top and bottom of the balloon makes a pancake. This would give a very narrow vertical beamwidth, but a very large horizontal coverage. This type of antenna design can deliver very long communications distances. This design has one drawback, which is poor coverage below the antenna, as pictured in Figure . With high gain omnidirectional antennas, this problem can be partially solved by designing in something called downtilt. An antenna that uses downtilt is designed to radiate at a slight angle, rather than at 90 degrees from the vertical element. This does help for local coverage, but it reduces effectiveness of the long-range ability. Cellular antennas use downtilt. The Cisco 12dBi omnidirectional antenna has a downtilt of zero degrees, but can be mounted to provide downtilt.  

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