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In telecommunication, standing wave ratio (SWR) is the ratio of the amplitude of a standing wave at an anti-node (minimum) to the amplitude at an adjacent node (maximum).
The standing wave ratio in a uniform transmission line is given by SWR = (1 + ρ)/(1 - ρ) where ρ is the reflection coefficient.
Reflections occur as a result of discontinuities, such as an imperfection in an otherwise uniform transmission line, or when a transmission line is terminated with other than its characteristic impedance.
Source: from Federal Standard 1037C and from MIL-STD-188
