Physics:Characteristic admittance

A transmission line is drawn as two black wires. At a distance x into the line, there is current phasor I(x) traveling through each wire, and there is a voltage difference phasor V(x) between the wires (bottom voltage minus top voltage). If $Y_0$ is the characteristic admittance of the line, then $I(x)/V(x)=Y_0$ for a wave moving rightward, or $I(x)/V(x)=-Y_0$ for a wave moving leftward.

Characteristic admittance is the mathematical inverse of the characteristic impedance. The general expression for the characteristic admittance of a transmission line is:

$Y_0=\sqrt{\frac{G+j\omega C}{R+j\omega L}}$

where

$R$ is the resistance per unit length,

$L$ is the inductance per unit length,

$G$ is the conductance of the dielectric per unit length,

$C$ is the capacitance per unit length,

$j$ is the imaginary unit, and

$\omega$ is the angular frequency.

The current and voltage phasors on the line are related by the characteristic admittance as:

$\frac{I^{+}}{V^{+}}=Y_0=-\frac{I^{-}}{V^{-}}$

where the superscripts $+$ and $-$ represent forward- and backward-traveling waves, respectively.

See also

• Characteristic impedance

References

• Guile, A. E. (1977). Electrical Power Systems. ISBN 0-08-021729-X. 
• Pozar, D. M. (February 2004). Microwave Engineering (3rd ed.). ISBN 0-471-44878-8. 
• Ulaby, F. T. (2004). Fundamentals Of Applied Electromagnetics (media ed.). Prentice Hall. ISBN 0-13-185089-X.