The antenna gain is normally defined as the increase
in power radiated by an antenna in a particular direction
compared to a reference dipole, or a reference isotropic radiator.
Antenna gain is normally obtained by making an antenna
directional by altering its radiation pattern so that most of
the radiation is transmitted in a certain direction. The antenna
gain plays an important part in the ultimate performance
of a system and is closely associated with the transmitted
power and the receiver sensitivity employed. The maximum power gain
obtainable in practice is usually restricted by various factors such
as antenna size, weight and the need for mobility.