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The transmission line is represented as a two-port network as shown in the figure. The sending end voltage and current are expressed in terms of receiving end voltage and current for the network as VS = A VR + B IR IS = C VR + D IR where A, B, C, and D are generalized circuit constants. The condition for symmetry for the network is

The transmission line is represented as a two-port network as shown in the figure. The sending end voltage and current are expressed in terms of receiving end voltage and current for the network as VS = A VR + B IR IS = C VR + D IR where A, B, C, and D are generalized circuit constants. The condition for symmetry for the network is Correct Answer A = D

Conditions for Reciprocity and Symmetry:

1) A network is said to be reciprocal if the ratio of the response to the excitation is invariant to an interchange of the positions of the excitation and response of the network.

2) A two-port network is said to be symmetrical if the input and output ports can be interchanged without altering the port voltages and currents.

  • ABCD parameters are generalized circuit constants used to develop the model for transmission lines, i.e. ABCD parameters are used in the two-port network representation of a transmission line.
  • ABCD parameters are also known as transmission line parameters.
  • The symmetry condition for a two-port network in terms of transmission parameters is: A = D

 

Important Notes:

Conditions of reciprocity and symmetry in terms of different two-port parameters are:

Parameter

Conditions of reciprocity

Conditions of symmetry

Z

z12 = z21

z11 = z22

Y

y12 = y21

y11 = y22

ABCD

(AD – BC) = 1

A = D

h

h12 = -h21

(h11h22 – h12h21)

= 1

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