A measure of impedance match, given by the length or magnitude of the vector that measures the distance between the impedance in question and the characteristic impedance. Input reflection coefficient is equal to the magnitude of the s parameter s₁₁; output reflection coefficient is equal to the magnitude of the s parameter s₂₂.

VSWR or voltage standing wave ratio can be calculated from the reflection coefficient using the equation

VSWR = [1 + ] / [ 1 - ]

In general, needs to be less than 0.5 (corresponding to a VSWR of 3:1) to have an acceptable impedance match. For good results in a cascade, should be on the order of 0.2 (VSWR of 1.5:1) or less.

See also s-parameters