i. Polarization of antennas.
(1) General. Radio waves transmitted from a vertical antenna are vertically polarized and
those transmitted from a horizontal antenna are horizontally polarized. Either type of polarization may
be used, but the performance will vary under certain conditions. In all cases, the polarization of the
receiving antenna must be the same as the transmitting antenna, otherwise, the loss of signal strength
may be great enough to prevent communications.
(2) Advantages of vertical polarization.
(a) Vertically polarized waves are less affected by aircraft flying over the transmission path
than are horizontally polarized waves.
(b) Vertically polarized antennas are more efficient for transmission over sea water at
frequencies lower than 100 MHz. Ordinary line-of-sight antennas, less than 45 to 50 feet (15 meters)
high, work best when vertically polarized. At higher frequencies, there is little difference in
performance.
(3) Advantages of horizontal polarization.
(a) Horizontal antennas are less likely to pick up manmade electrical interference such as
that which comes from power lines and transformers. Such interference is usually vertically polarized.
(b) In fairly dense forests, horizontally polarized waves suffer less loss than vertically
polarized waves. Also, standing wave effects are not as pronounced with horizontal polarization.
Standing wave effects can cause great variation in the field strength of vertically polarized waves when
antennas are moved among trees or buildings.
(c) In very dense jungles, there is no advantage in either type of polarization. Performance is
poor in this environment for all types of polarization.
(4) Cross polarization. In this configuration, the transmit and receive antennas at a
multichannel station are oppositely polarized. Depending on equipment capabilities, the transmit and
receive antennas may be mounted on a common mast or on separate masts. Cross polarization is
normally used to reduce the required transmitter-to-receiver frequency separation.
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