Both return loss and VSWR is used as a measure of reflection of E-M waves over coaxial cable or RF cable or microstrip line. It gives how much power is reflected and how much power is absorbed at various points specially at terminating and source points and at places of impedance discontinuities. Return Loss in a coaxial cable having Z0 as characteristic impedance and ZL as terminating or load impedance can be expressed as follows:

Return Loss (dB) = 20*Log10((ZL-Z0)/(ZL+Z0))

Where Z0= (L/C)0.5

Both Return loss and VSWR are related as mentioned in the following expression.

Return loss = 20 log ((VSWR+1) / (VSWR-1))

VSWR ranges from 1 to infinity.