Open Circuited Transmission Line

When the transmission line is opened from the load end, it is known as open circuited transmission line.

As shown in the diagram, at the open circuited end the current is minimum and voltage is maximum. At each λ/2 interval this behavior is repeated if we move away from the load end towards the source.

As shown in the diagram, that at λ/4 from the opened end the behavior of the voltage and current is vice versa to the short circuited transmission line. It means that at λ/4 from the opened end the voltage is minimum and current is maximum. This behavior is also repeated at λ/2 interval from the same point, or at the odd multiples of λ/4 on the transmission line.

As the current at the opened circuit end be maximum. At λ/4 away from the opened circuit point the impedance will be minimum because the current is maximum possible.

Characteristics

There are the following characteristics of open circuited transmission line.

1. The voltage standing wave ratio of the open circuited transmission line is infinity.
2. The magnitude of voltage reflection co-efficient is one.
3. The phase angle of voltage reflection co-efficient for the open circuited transmission line is in phase.
4. The first node of maximum voltage is at λ/2.
5. The first voltage maximum node is at λ/2 away from the open end point.
6. The current is minimum and voltage is maximum at λ/4 distance from the open circuited point.
7. The current is minimum and voltage is maximum at the open circuited point.

Input Impedance of Open Circuited Transmission Line

As shown in the given diagram the open circuited transmission line behaves as parallel resonant at the open circuited end. The minimum current flow takes place at open circuited end.

At λ/2 away from the open end of the transmission towards the source, the behavior at this point will be capacitive. This behavior will repeat 5λ/8 from the open circuit end.

At λ/4 of open circuit end of the transmission line, the circuit will behave as a series resonant circuit. It is due to the reason that the current will be maximum possible.

At 3λ/8 is the open terminal at transmission line, the behavior will be inductive.

At 7λ/8 the same behavior is repeated and so on.

The behavior of open circuited transmission line is a parallel resonant circuit or series resonant circuit or capacitive or inductive will repeat itself in the same manner towards the source at each λ/2 intervals, if the transmission line is long enough.