The
propagation constant of an
electromagnetic wave is a measure of the change undergone by the amplitude of the wave as it
propagates in a given direction. The quantity being measured can be the
voltage or
current in a circuit or a field vector such as
electric field strength or
flux density. The propagation constant itself measures change per unit length but is otherwise dimensionless. In the context of
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.