Figure 16. Example of a Direction Lobe.
e. Polarization.
(1) Polarization of a radiated wave is determined by the direction of the lines of force making
up the magnetic field. If the lines of electric force are at the right angles to the surface of the earth, the
wave is said to be vertically polarized. If the lines of electric force are parallel to the surface of the
earth, the wave is said to be horizontally polarized.
(2) Maximum energy transfer results when a receiving antenna is so oriented that its polarity
lies in the same plane as the electric field component of the transmitting antenna. Thus, a vertical
antenna is used for efficient reception of vertically polarized waves, and a horizontal antenna is used for
the reception of horizontally polarized waves. In some cases, the field rotates as the waves travel
through space. Under these conditions, both horizontal and vertical components of the field exist and
the wave is said to have elliptical polarization.
f. Directivity. Antennas used in multichannel systems possess high directivity. They
concentrate radiation in a given direction and minimize radiation in other directions. Because
wave lengths in the VHF and UHF ranges are short, it is practical to use antennas of such directivity
and gain that moderately low power can provide reliable communications. The high directivity
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