___________________________________________________ Principles of Transmission Lines
There are a variety of terminations for RF lines. Each termination has an
effect on the standing waves on the line.
Figure 3-Sum 16. Various Termination Effects on Standing Waves
A transmission line can be terminated in its characteristic impedance as an
open- or short-circuit, or in capacitance or inductance.
Whenever the termination on a transmission line is not equal to Z0, there are
reflections on the line. The amount of voltage reflected may be found by using
the equation:
(
)
RL -ZO
ER = Ei
RL +ZO
When the termination on a transmission line equals Z0, there is no reflected
voltage.
The measurement of standing waves on a transmission line yields
information about operating conditions. If there are no standing waves, the
termination for that line is correct and maximum power transfer takes place.
The standing-wave ratio is the measurement of maximum voltage (current)
to minimum voltage (current) on a transmission line and measures the
perfection of the termination of the line. A ratio of 1:1 describes a line
terminated in its characteristic impedance.
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