Editing Propagation constant (section)

{{Short description|Measure of change in amplitude and phase of a wave}}
{{Redirect|Transmission parameter|ABCD transmission parameters|two-port network#ABCD-parameters|scattering transfer parameters|scattering parameters#Scattering transfer parameters}}
{{Use American English|date=October 2024}}

The '''propagation constant''' of a sinusoidal [[electromagnetic wave]] is a measure of the change undergone by the [[amplitude]] and [[phase (waves)|phase]] of the wave as it [[wave propagation|propagates]] in a given direction. The quantity being measured can be the [[voltage]], the [[electric current|current]] in a [[electronic circuit|circuit]], or a field vector such as [[electric field strength]] or [[flux density]]. The propagation constant itself measures the [[dimensionless]] change in magnitude or phase [[per unit length]]. In the context of [[Two port networks|two-port networks]] and their cascades, '''propagation constant '''measures the change undergone by the source quantity as it propagates from one port to the next.

The propagation constant's value is expressed [[logarithm]]ically, almost universally to the base ''[[e (mathematical constant)|e]]'', rather than base 10 that is used in [[telecommunications]] in other situations. The quantity measured, such as voltage, is expressed as a sinusoidal [[phasor]]. The phase of the sinusoid varies with distance which results in the propagation constant being a [[complex number]], the [[imaginary number|imaginary]] part being caused by the phase change.