Return Loss is a measure of the amount of energy that is reflected back at a discontinuity in a Radio Frequency Circuit . It is specified in dB.
This calculator converts Return loss to Voltage Standing Wave Ratio or VSWR.
VSWR = (1 + 10-RL/20)/(1 – 10-RL/20)
A Return Loss of 10 dB is equivalent to a VSWR of 1.93. Note that VSWR has no units.
What is Return Loss?
Return loss is the ratio between the incident and reflected energy at the input of an RF system. Mathematically it is represented as
Return Loss = Incident Power / Reflected Power
In a good design, no power is reflected back. However in actual practice, there’s always some power that is returned back to the source on account of impedance mismatch.
A good design goal is to aim for a return loss of at least 14 dB across the specified frequency range.
 Return Loss