ProSoft Technology RLXIB-IHA-A - Manual (Page 93)

RLXIB-IHA ♦ 802.11a Reference
RadioLinx® 802.11a Industrial Hotspot User Manual
ProSoft Technology, Inc. Page 93 of 123
July 25, 2013
An antenna pattern with equal or nearly equal intensity in all directions is
omnidirectional. In two dimensions, an omnidirectional pattern appears as a
circle (in three dimensions, an omnidirectional antenna pattern would be a
sphere, but no antenna has true omnidirectional pattern in three dimensions). An
antenna is considered omnidirectional if one of its two dimensional patterns,
either azimuth or elevation pattern, is omnidirectional.
Beamwidth is an angular measurement of how strongly the power is
concentrated in a particular direction. Beamwidth is a three dimensional quantity
but can be broken into two-dimensional slices just like the antenna pattern. The
beamwidth of an omnidirectional pattern is 360 degrees because the power is
equal in all directions.
6.3.2 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
beamwidth, 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.
6.3.3 Antenna Polarity
Antenna polarization refers to the direction in which the electromagnetic field
lines point as energy radiates away from the antenna. In general, the polarization
is elliptical. The simplest and most common form of this elliptical polarization is a
straight line, or linear polarization. Of the transmitted power that reaches the
receiving antenna, only the portion that has the same polarization as the
receiving antenna polarization is actually received. For example, if the
transmitting antenna polarization is pointed in the vertical direction (vertical
polarization, for short), and the receiving antenna also has vertical polarization,
the maximum amount of power possible will be received. On the other hand, if
the transmit antenna has vertical polarization and the receiving antenna has
horizontal polarization, no power should be received. If the two antennas have
linear polarizations oriented at 45° to each other, half of the possible maximum
power will be received.