Figure 133.
Horizontal and Vertical Polarization.
c. The importance of knowing the polarization of an antenna is this: a
receiving antenna usually picks up more energy when it is polarized the same
way as the transmitting antenna. That's why all TV receiving antennas are
horizontal, because the TV transmitting antennas are horizontal.
d. That completes the brief review of antenna fundamentals. Now, let's
look at some new antenna characteristics.
The two main ones that apply
especially to radar antennas are directivity and radiation pattern. Both of
these antenna properties work together.
7.
Directivity and radiation pattern.
a. A directive antenna radiates energy in only one direction
and
receives energy from only one direction.
If the antenna radiates
and
receives signals in many directions, it has poor directivity.
If
the
antenna transmits and receives signals from only one direction, it has
good
directivity.
b. Figure 134 shows how energy radiates in all directions from a dipole
antenna.
The doughnut-shaped pattern shows you the radiation field of a
transmitting antenna.
When used to represent a receiving antenna, the
pattern indicates the areas from which signals will be received.
This
diagram is called a radiation pattern.
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