Glossary Of Common Antenna Terminology - Nortel 2332 Installation Manual

Glossary of common antenna terminology

The following glossary includes basic antenna terminology that can help in the selection and/or recommendation of a
particular antenna. These terms are used throughout the remainder of the document:
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 orien-
tation 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. A directional antenna must be "aimed" 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.
12.5 mW = 11 dBm
11 dBm + 9dBi = 20 dBm
20 dBm = 100 mW
100mw/12.5 mW = 8 times more power
E-Plane graph – The elevation plane graph shows the radiated antenna coverage pattern as a vertical cross section - as if
looking directly at the antenna from the side.
H-Plane graph – The horizontal plane graph shows the radiated antenna coverage pattern as a horizontal cross section -
as if looking directly at the antenna from above.
Nortel WLAN Series 2332 Access Point Installation Guide
External Antennas 123
For example: