Wave amplitude formula_4 described by the equation: where The units of the amplitude depend on the type of wave. Transverse mechanical waves (e.g., a wave on a string) have an amplitude expressed as a distance (e.g., meters), longitudinal mechanical waves (e.g., sound waves) use units of pressure (e.g., pascals), and electromagnetic waves (a form of transverse vacuum wave) express the amplitude in terms of its electric field (e.g., volts/meter). The wavelength formula_30 is the distance between two sequential crests or troughs (or other equivalent points), generally is measured in meters. A wavenumber formula_17, the spatial frequency of the wave in radians
Propagation constant of transmission lines, the term transmission coefficient has a different meaning despite the similarity of name: it is the companion of the reflection coefficient. The propagation constant, symbol formula_1, for a given system is defined by the ratio of the complex amplitude at the source of the wave to the complex amplitude at some distance "x", such that, Since the propagation constant is a complex quantity we can write: where That "β" does indeed represent phase can be seen from Euler's formula: which is a sinusoid which varies in phase as "θ" varies but does not vary in amplitude because