TC 9-64 _________________________________________________________________________
4-18. The coupling device (coupling coil) connects the transmitter to the
feeder. The feeder is a transmission line that carries energy to the antenna.
The antenna radiates this energy into space.
4-19. The factors that determine the type, size, and shape of the antenna are
as follows:
The frequency of operation of the transmitter.
Amount of power to be radiated.
General direction of the receiving set.
Some typical antennas are illustrated in figure 4-4.
Figure 4-4. Typical Antennas
CURRENT AND VOLTAGE DISTRIBUTION ON AN ANTENNA
4-20. A current flowing in a wire whose length is properly related to the RF
produces an electromagnetic field. This field is radiated from the wire and is
set free in space. We discuss how these waves are set free later in this
chapter. Remember, the principles of radiation of electromagnetic energy are
based on two laws:
A moving electric field creates a magnetic (H) field.
A moving magnetic field creates an electric (E) field.
4-21. In space, these two fields are in phase and perpendicular to each other
at any given time. Although a conductor is usually considered present when a
moving electric or magnetic field is mentioned, the laws that govern these
4-6
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