________________________________________________________________Wave Propagation
ELECTROMAGNETIC WAVES
1-115. In general, the same principles and properties of light waves apply to
the communications electromagnetic waves you are about to study. The
electromagnetic field is used to transfer energy (as communications) from
point to point. The basic antenna is a propagation source of these
electromagnetic waves.
THE BASIC ANTENNA
1-116. The study of antennas and electromagnetic wave propagation is
essential to a complete understanding of radio communication, radar, loran,
and other electronic systems. Figure 1-23 shows a simple radio
communication system. In the illustration, the transmitter is an electronic
device that generates radio-frequency energy. The energy travels through a
transmission line (discussed in chapter 3) to an antenna. The antenna
converts the energy into radio waves that radiate into space from the
antenna at the speed of light. The radio waves travel through the atmosphere
or space until they are either reflected by an object or absorbed. If another
antenna is placed in the path of the radio waves, it absorbs part of the waves
and converts them to energy. This energy travels through another
transmission line and is fed to a receiver. From this example, you can see
that the requirements for a simple communications system are as follows:
Transmitting equipment.
Transmission line.
Transmitting antenna.
Medium.
Receiving antenna.
Receiving equipment.
Figure 1-23. Simple Radio Communication System
1-33
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