Figure 8.
Possible routes for ground waves.
8.
POLARIZATION.
Polarization of a radiated wave is determined by the
direction of the lines of force making up the electrical field.
If the
lines of force are at right angles to the surface of the earth, as radiated
from a vertically mounted antenna, the wave is said to be vertically
polarized (Fig 9).
If the lines of electrical force are parallel to the
surface of the earth, as radiated from a horizontally mounted antenna, the
wave is said to be horizontally polarized (Fig 10). The polarization of the
wave front is an important factor in the effective transmission and
reception of radio signals.
Thus, if a single wire antenna is used to
extract energy from a passing radio wave, maximum pickup will result when
the antenna is physically positioned so that it lies in the same direction
as the electrical component of the radiation field.
A vertical antenna
(mounted perpendicular to the ground) should be used for the effective
reception of vertically polarized waves (those transmitted from a vertical
antenna).
A horizontal antenna should be used for the reception of
horizontally polarized waves (those transmitted from a horizontally mounted
antenna).
In both cases, the direction of travel is considered to be
parallel to the surface of the earth (Figs 9 and 10).
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