The Omnidirectional antenna is probably the most common antenna available. Just about every Wi-Fi device you can buy comes with an omni antenna. This is because the omni is so easy to set up, and generally works in consumer environments without much planning . There are few different types of omni antennas. Omni signals spread out sideways , but not vertically.
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| Top view of coverage an Omni Antenna |
An omni antenna sends and receives signals equally in front, behind , to the left , or to the right of the antenna. However, when you go above or below the antenna, signal strength drops off significantly. The trade-off you make when choosing a high-gain antenna is this focusing, or thinning, of the above and below energy. The low-gain omni works better vertically than a high-gain omni, but it won't extend as far horizontally. The omnidirectional antenna sends and receives signals in all directions equally. This is generalization , but it's mostly accurate.
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| Side view of an omnidirectional antenna signal |
Even though an omni antenna does not work very well above and below, it is not considered a directional antenna. Wi-Fi antennas are generally rated in two-dimensional space that assumes it is mounted parallel to the Earth's surface. Knowing how the beam is shaped, and that an antenna is not truly omnidirectional will help you choose the right antenna for your Wi-Fi.
(source : Wi-Fi Toys Extreme Tech)
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