In a wireless system, antenna are used to convert electrical waves into electromagnetic waves. The amount of energy the antenna can "boost" the sent and received signal by is referred to as the antenna Gain.
- Antenna gain is normally given in isotropic decibels [dBi]. It's the power gain in comparison to an isotropic antenna (antenna that spread energy in every directions with the same power....theoretical view it doesn't exist in reality!).
- Some antennas have their gain expressed in Desible [dBd], it's the gain compared to a dipole antenna. In this case you have to add 2.14 to obtain the corresponding gain in [dBi].
- The more an antenna has gain the more it is directive (wave sent in a preferred direction).
- Antenna coming with WLAN kits are generally without much gain (2.14 dBi ).
- Antenna gain is the same for transmit and receive
Parabolic antenna:
The parabolic reflector is independant of the frequency, it only affects antenna gain. So it means you can reuse your TV satellite dish for wifi :-)
The higher the gain directivity and so the more accurately it must be pointed.
The big challenge is to illuminate the parabolic reflector correctly. If illumination is too large or to concentrated there will be gain loss.
Antenna gain is measured in:
dBi - relative to an isotropic radiator
dBd - relative to a dipole radiator
The relationship between dBd and dBi can be represented in the following equation
0 dBd = 2.15 dBi
In most cases, we use dBi as our antenna gain measurement.
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