Wireless Antenna properties
An antenna has
three main properties: direction, gain and polarization.
Wireless Antenna Gain is term used for measuring of
increase in signal power, as decibels (dB). Antenna with a higher gain
is more effective in it's radiation pattern.
Every antenna is designed to raise the power in the wanted direction and
reduce it in unwanted directions. Gain of an antenna is reciprocal,
meaning it is the same for transmitting and receiving.
Antenna Direction is the shape of the wireless signal
after leaving the antenna.
Polarization of the wireless antenna is the orientation
of the wireless signal.
It can be vertical, horizontal, circular or combinations of these.
The E-plane and H-plane are reference planes for linearly polarized antenna
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This diagram showing the relationship between the E and H planes for a horizontally polarized directional antenna |
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This diagram showing
the relationship between the E and H planes for a vertically polarized
omni-directional dipole antenna
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Wireless antenna Range
radio waves travel in straight lines and do not penetrate obstacles very
well
metal reflect the signal, modern houses may also have foil backed
plasterboard to meet fire regulations and modern glass has a metal
content.
This said, as a general rule 802.11b/g WiFi devices will cover a house
quite well, not guaranteed though.
Bear in mind if your wifi antenna is stuck down behind the computer case
if already has two layers of steel or a wall to penetrate first.
When you replace the antenna onto a wireless device, the antenna gain
acts on both the transmit power and receiver sensitivity, so you are not
only sending your signal further but you are also able to receive much
weaker signals.
approximate Line of sight antenna range in free space (outside)
from standard UK Wireless device with antenna both ends at given gain
level.
|
Antenna gain |
Wireless range |
|
0dB |
200m |
|
4dB |
440m |
|
7dB |
620m |
|
10dB |
1.2km |
|
13dB |
2.8km |
|
16dB |
5.0km |
|
20dB |
12.5Km |
|
24dB |
31Km |
The table is only a rough guide as
conditions site to site vary wildly.
