VSWR (Voltage Standing Wave Ratio) VSWR is a measurement of the level of standing waves on a feeder. VSWR is defined as the ratio of the maximum voltage to the minimum voltage in a standing wave pattern along the length of a transmission line structure. Standing waves represent the power that is not accepted by the load and reflected back along the transmission line or feeder.  It varies from 1 to (plus) infinity and is always positive.  Impedance mismatches are the reason for standing waves along the transmission line.

Reflection Coefficient is defined as the ratio of the reflected wave to incident wave at a reference plane.  This value varies from -1 (for a shorted load) to +1 (for an open load) and becomes 0 for matched impedance load. The reflection coefficient is a parameter that describes how much of an electromagnetic wave is reflected by an impedance discontinuity in the transmission medium. The voltage reflection coefficient  Γ determines the magnitude and phase of the reflected wave given the incident wave, the characteristic impedance of the transmission line, and the terminating impedance.

Return Loss is a quantity often used within RF circuits where impedance matching is important. The return loss is the proportion of a signal that is reflected as a result of an impedance mismatch. Return loss is related to both standing wave ratio (SWR) and reflection coefficient (Γ). Increasing return loss corresponds to lower SWR. Return loss is a measure of how well devices or lines are matched. A match is good if the return loss is high. A high return loss is desirable and results in a lower insertion loss.