Standing wave ratio
Standing waves have already been mentioned, together with their formation due to load termination. Figure 7.4 shows the result of producing standing waves on a transmission line. Remember that standing waves are produced when two waves having the same frequency and amplitude and travelling in opposite directions are superimposed. The figure shows that standing waves produce points of minimum and maximum disturbance called nodes and antinodes, and this applies to voltage or current waves.
Associated with standing waves is the standing wave ratio which indicates the amount of reflected energy relative to the incident energy which is absorbed at the termination. Several forms of this are derived below. At a voltage maximum
Hence
Dividing numerator and denominator by Vl gives
It has already been stated that hence
Also the power absorbed in the termination and the power reflected are given respectively by
Hence
Since then
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