ABSTRACT
In order to distinguish between the two types of
reference antenna we use subscripts i and d to
denote isotropic and half-wave dipole reference
antennas respectively. As an example, an aerial
having a gain of 10 dBi produces ten times power
gain when compared with a theoretical isotropic
radiator. Similarly, an antenna having a gain of
13 dBd produces twenty times power gain when
compared with a half-wave dipole. Putting this
another way, to maintain the same field strength
at a given point, you would have to apply 20 W to
a half-wave dipole or just 1 W to the antenna in
question! Some comparative values of antenna
gain are shown on page 28.
