User's Manual

Page 9 of 11 6/17/2003
Antenna Descriptions
When selecting antennas to install with the OS2400-HSE in the U.S. and Canada, you can only use
models that are specifically approved by the U.S. Federal Communications Commission (FCC) and
Industry Canada. See Approved antennas for more details.
You must also consider three important electrical characteristics when selecting antennas:
• Antenna pattern
• Antenna gain
• Antenna polarity
Antenna pattern
Information between radios is transferred via electromagnetic energy radiated by one antenna and
received by the second. More power is radiated in certain directions from the antenna than others, a
phenomenon known as the antenna pattern. Each antenna should be mounted so the direction of strong
radiation intensity points toward the other antenna(s) to which it is linking.
Although complete antenna patterns are three-dimensional (3D), a two-dimensional (2D) slice of the
pattern is often shown because the antennas of interest are often located horizontally from one another,
along the ground rather than above or below each other.
A slice taken in a horizontal plane through the center (or looking down on the pattern) is called the
azimuth pattern. A vertical plane slice, which is seen from the side, is the elevation pattern.
An antenna pattern that has equal or nearly equal intensity in all directions is omnidirectional. In two
dimensions, an omnidirectional pattern is a circle. An antenna is considered omnidirectional if one of its
2D patterns is omnidirectional. (No antenna has an omnidirectional pattern in 3D.)
Beam width is an angular measurement of how strongly the power is concentrated in a particular
direction. Beam width is a 3D quantity, but it can be broken into 2D slices just like the antenna pattern.
The beam width of an omnidirectional pattern is 360°, because the power is equal in all directions.
Antenna gain
Antenna gain is a measure of how strongly an antenna radiates in its direction of maximum radiation
intensity compared to how strong the radiation would be if the same power were applied to an antenna
that radiated all of its power equally in all directions. Using the antenna pattern, the gain is the distance to
the furthest point on the pattern from the origin. For an omnidirectional pattern, the gain is 1, or
equivalently 0 dB. The higher the antenna gain is, the narrower the beam width, and vice versa.
The amount of power received by the receiving antenna is proportional to the transmitter power multiplied
by the transmit antenna gain, multiplied by the receiving antenna gain. Therefore, the antenna gains and
transmitting power can be traded off. For example, doubling one antenna gain has the same effect as
doubling the transmitting power. Doubling both antenna gains has the same effect as quadrupling the
transmitting power.