Half & Quarter Wave Length Transmission Lines

Half Wave Length Transmission Line

As shown in the given diagram the half wave length transmission line can be open circuited or short circuited. The length of the transmission line is valid only for the particular frequency at which λ/2 of that transmission line is calculated other than that frequency. The transmission line will not behave as a half wave length line.

As shown in the diagram No. (a), the half wave length transmission line is open circuited. In this case at the load end or at the last end the voltage will be maximum and the current will be minimum. This behavior is repeated at the starting end of the same transmission line. It means that at this starting end of half wave length transmission line the voltage will be also maximum and the current will be minimum.

Half Wave Length Transmission Line Open & Short Circuited Diagram
Half Wave Length Transmission Line Open & Short Circuited Diagram

As shown in the diagram No. (b) The half wave length transmission line is short circuited. In this case at the load end or at the last end the voltage will be minimum and the current will be maximum. This behavior is repeated at the starting end of the same transmission line. It means that at the starting end of half wave length line the voltage will be also minimum and the current will be maximum.

Quarter Wave Length Transmission Line

As shown in the given diagram the quarter wave length transmission line can be open circuited or short circuited. The length of the transmission line is valid only for particular frequency at which λ/4 of the transmission line is calculated other than that frequency the transmission line will not behave as a quarter wave length transmission line.

Quarter Wave Length Transmission Line Open & Short Circuit Diagram
Quarter Wave Length Transmission Line Open & Short Circuit Diagram

As shown in the diagram No. (c) The quarter wave length transmission line is open circuited. In this case at the load or at the last end the voltage will be maximum and the current will be minimum. This behavior is repeated at the starting end of the same transmission line. It means that at the starting end of the quarter wave length transmission line the voltage will also be maximum and the current will be minimum.

As shown in the diagram No. (d) The quarter wave length transmission line is short circuited, in this case at the load end or at the last end the voltage will be minimum, and the current will be maximum, this behavior is repeated at the starting end of the same transmission line. It means that at the starting end of the quarter wave length transmission line the voltage will be maximum and the current will be minimum.

The quarter wave length transmission line is used for the matching purposes of the impedance. It is known as stub matching of the load impedance.

Quarter Wave Length Transmission Line Impedance Formula

Zo = Characteristics Impedance
Zs = Source Impedance