chapter  2
6 The Yagi beam antenna
Pages 2

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.