TC 9-64 _________________________________________________________________________
POLARIZATION
2-33. For maximum absorption of energy from the electromagnetic fields, the
receiving antenna must be located in the plane of polarization. This places
the conductor of the antenna at right angles to the magnetic lines of force
moving through the antenna and parallel to the electric lines, causing
maximum induction.
2-34. Normally, the plane of polarization of a radio wave is the plane in
which the E field propagates with respect to the earth. If the E field
component of the radiated wave travels in a plane perpendicular to the
earth's surface (vertical), the radiation is said to be vertically polarized, as
shown in figure 2-5, view A. If the E field propagates in a plane parallel to
the earth's surface (horizontal), the radiation is said to be horizontally
polarized, as shown in view B.
Figure 2-5. Vertical and Horizontal Polarization
2-35. The position of the antenna in space is important because it affects the
polarization of the electromagnetic wave. When the transmitting antenna is
close to the ground, vertically polarized waves cause greater signal strength
along the earth's surface. On the other hand, antennas high above the ground
should be horizontally polarized to get the greatest possible signal strength to
the earth's surface. Vertically and horizontally polarized antennas are
discussed in more detail in chapter 4.
2-36. The radiated energy from an antenna is in the form of an expanding
sphere. Any small section of this sphere is perpendicular to the direction the
energy travels and is called a wavefront. All energy on a wavefront is in
phase. Usually all points on the wavefront are at equal distances from the
antenna. The farther the wavefront is from the antenna, the less spherical
2-10
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