Chapter 3
Principles of Transmission Lines
LEARNING OBJECTIVES
3-1.
Upon completing this chapter, you should be able to do the following:
State what a transmission line is and how transmission lines are
used.
Explain the operating principles of transmission lines.
Describe the five types of transmission lines.
State the length of a transmission line.
Explain the theory of the transmission line.
Define the term "lumped constants" in relation to a transmission line.
Define the term "distributed constants" in relation to a transmission
line.
Define leakage current.
Describe how the electromagnetic lines of force around a transmission
line are affected by the distributed constants.
Define the term "characteristic impedance" and explain how it affects
the transfer of energy along a transmission line.
State how the energy transfer along a transmission line is affected by
characteristic impedance and the infinite line.
Identify the cause of and describe the characteristics of reflections on
a transmission line.
Define the term "standing waves" as applied to a transmission line.
Describe how standing waves are produced on a transmission line
and identify the types of terminations.
Describe the types of standing-wave ratios.
INTRODUCTION TO TRANSMISSION LINES
3-2. A transmission line is a device designed to guide electrical energy from
one point to another. It is used, for example, to transfer the output RF energy
of a transmitter to an antenna. This energy will not travel through normal
electrical wire without great losses. Although the antenna can be connected
directly to the transmitter, the antenna is usually located some distance
away from the transmitter. A transmission line is used to connect the
transmitter and the antenna.
3-3. The transmission line has a single purpose for both the transmitter and
the antenna. This purpose is to transfer the energy output of the transmitter
to the antenna with the least possible power loss. How well this is done
depends on the special physical and electrical characteristics (impedance and
resistance) of the transmission line.
3-1
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