When a wave, whether light wave, sound wave or radio wave, hits a medium, it is reflected, absorbed and transmitted by the medium. The reflection, absorption and transmission determine the proportion of energy that is reflected, absorbed and transmitted by the medium.
The evaluation of the three physical properties is based on the quotients respectively of the reflected, absorbed or transmitted energy to the energy incident on the medium. The evaluation quantities are the reflection coefficient, the absorption coefficient and the transmittance.
The reflection coefficient, Reflection Coefficient, is also a measure of impedance matching ofcables and circuits. It is a frequency-dependent vector whose angle can be used to determine the type and magnitude of reflection. Unlike the standing wave ratio( VSWR), which cannot distinguish between a short-circuited and an open circuit termination, the reflection coefficient offers this possibility. It is given in the Greek capital letter gamma (`Gamma`) and is directly related to the standing wave ratio and return loss.
The reflection coefficient, referred to as return loss for cables and optical fib ers, can assume values between 0.0 and 1.0. If the matching is impedance-correct, i.e. if there are no reflections and no standing waves, the reflection coefficient is 0.0; if the matching is open or short-circuited, the value is +1.0 or -1.0, respectively; the angle of the vector is 180° in the first case, with open termination, and 0° in the second case.
As a graphical representation for reflection coefficients, the Smith chart is suitable, with which the complex impedances and admittances can be represented with their real and imaginary parts.