A two-port network has four terminals labeled A, B, C, and D, with A and B as the input ports and C and D as the output ports. The voltages and currents at the input and output ports are related by ABCD parameters, which are constants that describe the network's performance. The ABCD parameters can be represented in a transmission matrix and are used to analyze electrical networks and determine input/output voltages and currents. Specific ABCD parameters are defined for open circuit, short circuit, and symmetrical network configurations.

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By: Vidhyavati Suryawanshi
Lecturer (Electrical Engineering Dept)
ABCD Parameters

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ABCD Parameters of Transmission Line
 Transmission of power from generating unit to distributing units
can be done through the transmission line. During transmission,
many losses occur in the transmission line which decreases the
efficiency of a line. For improving the proficiency of the
transmission, two port networks are used.

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 A network having two input and two output terminals is known as a two port
network. The network shown below has four terminals in which A and B
represents the input port where as C and D represents the output port.
 port-network The voltage and current in the output and input terminals of a
two-port network are given by the equations shown below

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 Vs = sending end voltage
 Is = sending end current
 Vr = receiving end voltage
 Ir = receiving end current
 A, B, C and D are the constants also known as the transmission parameters
or chain parameters. These parameters are used for the analysis of an
electrical network. It is also used for determining the performance of input,
output voltage and current of the transmission network.

5. z equations can also be written in a matrix form for easy
calculations shown below
The matrix transmission-matrix is called the transfer or transmission matrix
of the network.

6. z ABCD parameters for open circuit
In the open circuit, the output terminals are open, and the voltage measure across
them is Vr. Since the circuit is open at the receiving end, the current Ir remains zero.

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ABCD parameters for short circuit

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Relation between ABCD parameters
 For determining the relation between various types of network, like passive or
bilateral network reciprocity theorem is applied. The voltage V is applied to the
sending end, and the receiving end is kept short circuit, so the voltage becomes
zero.

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Consider, the network is passive, i.e. it contains only passive components in
the circuit like inductance, resistance, etc. So the current remains same Is = Ir.

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dividing the above equation from -V/B we get
This relation helps in determining the fourth parameters if we know any three
parameters.

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For a symmetrical network, the input and
output terminal may be interchanged
without affecting the network behaviour.

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Parameter Specification Unit
A = VS / VR Voltage ratio Unit less
B = VS / IR Short circuit resistance Ω
C = IS / VR Open circuit conductance mho
D = IS / IR Current ratio Unit less

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