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Common antenna terminology
The following glossary includes basic antenna terminology that can help in
the selection and recommendation of a particular antenna.
Omnidirectional (Omni)
Refers to the antenna coverage pattern. An omnidirectional antenna
creates a uniform coverage pattern. Most omnidirectional antennas
are weakest directly above and directly below their endpoints — this
characteristic creates the familiar dual-lobe pattern shown on the E-plane
graphs. Nulls are typically related to the orientation of the dipole/monopole
antenna relative to the horizontal or vertical planes. The lobes grow and
shrink depending upon the ground plane effects and cancellation/addition
of the radiating signal. Omnidirectional antennas are suitable for most
general deployments.
Directional
Refers to the antenna coverage pattern. A directional antenna focuses its
lobe or radiated energy in a particular direction. In general, as the gain of a
directional antenna increases, the radiating beamwidth or lobe decreases.
This design increases the transmitted power and communication distance
in a specific direction at the expense of uniform coverage, as compared
to an omnidirectional antenna. You must aim a directional antenna at the
intended coverage zone.
Gain
Expressed in dBi, indicates the relative increase in radiated power over an
isotropic point radiating source with a reference gain of 1.0.
Each 3 dB increment in power effectively doubles the radiated energy. For
example, an antenna with a gain of 9 dBi increases the transmit power 8
times more than an isotropic point radiating source. For example
12.5 mW = 11 dBm
11 dBm + 9dBi = 20 dBm
20 dBm = 100 mW
100mw/12.5 mW = 8 times more power
Avaya WLAN 8100
Installation–AP 8120
NN47251-302
01.AD
10 May 2010
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