What is the input impedance of short circuited transmission line?
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Standing waves at the resonant frequency points of an open- or short-circuited transmission line produce unusual effects. When the signal frequency is such that exactly 1/2 wave or some multiple thereof matches the line’s length, the source “sees” the load impedance as it is. The following pair of illustrations shows an open-circuited line operating at 1/2 (Figure below)
and 1 wavelength (Figure below) frequencies:

Source sees open, same as end of half wavelength line.

Source sees open, same as end of full wavelength (2x half wavelength line).
In either case, the line has voltage antinodes at both ends, and current nodes at both ends. That is to say, there is maximum voltage and minimum current at either end of the line, which corresponds to the condition of an open circuit. The fact that this condition exists at both ends of the line tells us that the line faithfully reproduces its terminating impedance at the source end, so that the source “sees” an open circuit where it connects to the transmission line, just as if it were directly open-circuited.
The same is true if the transmission line is terminated by a short: at signal frequencies corresponding to 1/2 wavelength (Figure below) or some multiple (Figure below) thereof, the source “sees” a short circuit, with minimum voltage and maximum current present at the connection points between source and transmission line:
and 1 wavelength (Figure below) frequencies:

Source sees open, same as end of half wavelength line.

Source sees open, same as end of full wavelength (2x half wavelength line).
In either case, the line has voltage antinodes at both ends, and current nodes at both ends. That is to say, there is maximum voltage and minimum current at either end of the line, which corresponds to the condition of an open circuit. The fact that this condition exists at both ends of the line tells us that the line faithfully reproduces its terminating impedance at the source end, so that the source “sees” an open circuit where it connects to the transmission line, just as if it were directly open-circuited.
The same is true if the transmission line is terminated by a short: at signal frequencies corresponding to 1/2 wavelength (Figure below) or some multiple (Figure below) thereof, the source “sees” a short circuit, with minimum voltage and maximum current present at the connection points between source and transmission line:
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