Two Port Network:

A port is a pair of nodes across which a device can be connected. The voltage is measured across the pair of nodes and the current going into one node is the same as the current coming out of the other node in the pair. These pairs are entry (or exit) points of the network.



So, a network with two input terminals and two output terminals is called a four-terminal network or a two-port network.

In a two-port network, there are two voltage variables and two current variables. According to the choice of input and output ports, these voltage and current variables can be arranged in different equations, giving rise to different port parameters.

Relationships of Two-Port variables

In order to describe the relationships among the port voltages and currents of an n-port network, ‘n’ number of linear equation is required. However, the choice of two independent and two dependent variables is dependent on the particular application. So, from four variables, we can select two variables as independent variables in 4c, = 6(nc.) different ways and hence, six sets of two port parameters for a given network


Types of parameters as mentioned below:

1. Open-circuit impedance parameters (Z-parameters)

2. Short-circuit admittance parameters (Y-parameters)

3. Transmission or chain parameters (T-parameters or ABCD- parameters)

4.Inverse transmission parameters (T’- parameters)

5.Hybrid parameters (h-parameters)

6. Inverse hybrid parameters (g-parameters)

Symmetrical Network

A symmetrical network is a network which is divided into two equal halves, with each half as a mirror image of the other.

In other words, if the network looks same from both the ports, then it is said to be Symmetrical, otherwise it is said to be Asymmetrical.

Reciprocal Network

If the network obeys Reciprocity theorem, then it is said to be reciprocal, otherwise it is said to be non- reciprocal.

All the passive networks are always reciprocal and all the active networks are always non-reciprocal.


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