4-13
used. In this section, we will introduce the basic types of radiation (isotropic and anisotropic) and their
radiation patterns.
Isotropic Radiation
Some antenna sources radiate energy equally in all directions. Radiation of this type is known as
ISOTROPIC RADIATION. We all know the Sun radiates energy in all directions. The energy radiated
from the Sun measured at any fixed distance and from any angle will be approximately the same. Assume
that a measuring device is moved around the Sun and stopped at the points indicated in figure 4-9 to make
a measurement of the amount of radiation. At any point around the circle, the distance from the measuring
device to the Sun is the same. The measured radiation will also be the same. The Sun is therefore
considered an isotropic radiator.
Figure 4-9.—Isotropic radiator.
To plot this pattern, we will assume that the radiation is measured on a scale of 0 to 10 units and that
the measured amount of radiation is 7 units at all points. We will then plot our measurements on two
different types of graphs, rectangular- and polar-coordinate graphs. The RECTANGULAR-
COORDINATE GRAPH of the measured radiation, shown in view A of figure 4-10, is a straight line
plotted against positions along the circle. View B shows the POLAR-COORDINATE GRAPH for the
same isotropic source.
