An antenna radiates energy in a particular pattern in free
possible to design an antenna system to provide us with the best
(a) An example of a source that radiates in all directions is the
sun. This type of radiator is called an isotropic radiator. If we
could measure the sun's radiation as we move around it in a circle,
we would find it was the same all along the circle.
The sun as an isotropic source of radiation.
(b) Another type of radiator is called anisotropic. An example
is a flashlight. The light beam radiates only a small portion of the
total space around the flashlight. If we move in a circle around the
flashlight, we find the level goes from zero to maximum then back to