Characteristic admittance

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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 is the characteristic admittance of the line, then for a wave moving rightward, or 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:


is the resistance per unit length,
is the inductance per unit length,
is the conductance of the dielectric per unit length,
is the capacitance per unit length,
is the imaginary unit, and
is the angular frequency.

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

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 ed.). ISBN 0-471-44878-8.
  • Ulaby, F. T. (2004). Fundamentals Of Applied Electromagnetics (media ed.). Prentice Hall. ISBN 0-13-185089-X.