Electromagnetic radiation and B fields in EMR are in-phase (see math section below). An important aspect of light's nature is its frequency. The frequency of a wave is its rate of oscillation and is measured in hertz, the SI unit of frequency, where one hertz is equal to one oscillation per second. Light usually has multiple frequencies that sum to form the resultant wave. Different frequencies undergo different angles of refraction, a phenomenon known as dispersion. A wave consists of successive troughs and crests, and the distance between two adjacent crests or troughs is called the wavelength. Waves of the electromagnetic spectrum
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