Short Circuited Transmission Line

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Behavior

When the transmission line in shorted from the load end, it is known as short circuited transmission line.

Short Circuited Transmission Line

As shown in the diagram at the short circuited end the current is maximum and voltage is minimum. At each λ/2 interval. This behavior is repeated if we move away form the load end towards the source. As shown in the diagram, that at λ/4 from from the shorted end the behavior of current and voltage is vice versa to previous case. It means that at λ/4 from shorted end the voltage is maximum and the current is minimum. This behavior is also repeated at each λ/2 interval from the same point or at the odd multiples of λ/4 on the transmission line.

As the current at the shorted end of the transmission line is maximum, therefore the impedance at this point will be minimum. At λ/4 away from the shorted end the impedance will be maximum because at this point the current is minimum possible.

Characteristics

There are the following characteristics of short circuited transmission line.

  1. the voltage standing wave ratio VSWR of the short circuited transmission line is infinity.
  2. The magnitude of voltage reflection co-efficient is one.
  3. The phase angle of voltage reflection co-effinient for the short circuited transmission line is 180o out of phase.
  4. The first current maximum node of the short circuited transmission line is λ/2 away from the shorted end towards the source.
  5. The first voltage transmission node is at λ/4 away from the shorted end towards the source.
  6. The current is minimum and voltage is maximum at λ/4 distance from the short circuited point.
  7. The current is maximum and voltage is minimum at the short circuited point.

Input Impedance

As shown in the given diagram, the short circuited transmission line behaves as series resonant circuit at the short circuited end because the maximum flow of current take place at the short circuited end.

Short Circuited Transmission Line Input Impedance

At λ/8 away from the shorted end of the transmission line towards the source, the behavior at this point will be inductive. This behavior will repeat at 5λ/8 from the short circuited end.

At λ/4 from the short circuited point of transmission line, the circuit will behave as parallel resonant circuit. It is due to the reason that at point the current is maximum possible.

At 3λ/8 form the shorting terminal of the transmission line the behavior will be capacitve. This behavior will repeat at 7λ/8 and so on.

The behavior of short circuited transmission line as a series resonant circuit or parallel resonant circuit or inductive or capacitive will repeat it self in the same manner toward the source at each λ/2 intervals if the transmission line is long enough.

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