b. Now, the reflected wave of the RF current travels away from the open
end of the line.
It meets the incident current waves coming from the
generator. At every point on the line, these two waves combine to produce a
resultant wave, called a standing wave. Part D of Figure 10 shows how the
incident and reflected waves combine to produce a standing wave.
21. Standing waves are stationary.
a. Figure 10 shows that the standing wave is stationary, it does not
move.
As the incident wave and reflected wave move past each other, the
standing wave changes only its amplitude. Let's see why this is so with the
help of Figure 11.
(1) Part A of Figure 11 shows the incident wave and the reflected
wave in phase. Adding the two current waves gives a resultant or standing
wave of current equal to twice the amplitude of the traveling waves.
(2) Part B of Figure 11 shows a 90 degree phase difference between
the incident and reflected current waves because they are moving away from
each other.
Notice that although the amplitude of the standing wave has
decreased, the minimum and maximum points lie in the same place as they did
in Part A of Figure 11.
(3) Part C of Figure 11 shows 180 degrees phase difference between
the incident and reflected waves. The two waves cancel each other. There
is no standing wave of current at this particular time.
(4) Part D of Figure 11 shows 270 degrees phase difference between
the two traveling waves. Notice now that, although the minimum and maximum
points are in the same position, the amplitude has reversed its direction.
(5) Part E of Figure 11 shows the two current waves in phase again.
The resultant wave is equal in amplitude but 180 degrees out of phase with
the standing wave shown in Part A of Figure 11.
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