ABCD Parameters of Two Port Network or Transmission Parameters or Chain Parameters:

ABCD Parameters of Two Port Network are known as transmission parameters. These are generally used in the analysis of power transmission in which the input port is referred as the sending end while the output port is referred as receiving end. These are obtained by expressing voltage V₁ and current I₁ at input port interms of voltage V₂ and current I₂ at output port. Thus, voltage V₂ and current I₂ are independent variables while voltage V₁ and current I₁ are dependent variables. Thus, we have

Generally we have considered the currents in both the ports are entering the port and both are positive. The negative sign with I₂ indicates that, for the ABCD parameters the current I₂ is leaving the port 2.

In equation form, above relations can be written as,

In matrix form above equations can be written

The individual transmission parameters are defined as follows,

This is called open circuit reverse voltage gain.

This is called open circuit transfer admittance

This is called short circuit transfer impedance

This is called short circuit reverse current gain.

ABCD or Transmission parameters are also called chain parameters.