Characteristic admittance

From Wikipedia, the free encyclopedia
Jump to: navigation, search
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}}


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[edit]


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