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 <math>Y_0</math> is the characteristic admittance of the line, then <math>I(x) / V(x) = Y_0</math> for a wave moving rightward, or <math>I(x)/V(x) = -Y_0</math> 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:

<math>Y_0=\sqrt{\frac{G+j\omega C}{R+j\omega L}}</math>

where

<math>R</math> is the resistance per unit length,

<math>L</math> is the inductance per unit length,

<math>G</math> is the conductance of the dielectric per unit length,

<math>C</math> is the capacitance per unit length,

<math>j</math> is the imaginary unit, and

<math>\omega</math> is the angular frequency.

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

<math>\frac{I^+}{V^+} = Y_0 = -\frac{I^-}{V^-}</math>

where the superscripts <math>+</math> and <math>-</math> 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.