VSWR to Return Loss Calculator

What is Return Loss?

Impedance mismatch/discontinuity between the transmission line/cable to the connected load/component leads to a small amount of incident signal power reflected back to the source. The return loss of a system is defined as the ratio of incident power to reflected power and is measured in dB. High return loss results in low reflected power, thus high return loss is desirable for a system.  

How to calculate the return loss?

VSWR (Voltage Standing Wave Ratio) measures the efficiency of power transferred from a source to a load via a transmission line/cable. Impedance mismatch between the transmission line/cable to the load is the main cause for the standing wave pattern along the transmission line. 

For an ideal system, there is no impedance mismatch between the transmission line & load, hence no reflection and standing wave. Thus, for this system, VSWR = 1:1 (i.e.,100 %   power transferred from a source to a load via a transmission line/cable). As we know that the definition of the return loss of a system is the ratio of incident power to reflected power. For an ideal system, reflected power is zero, so return loss is infinity (∞). 

But, for a practical system, there will be a small impedance mismatch. Hence, the return loss is always lower than the ideal system (i.e., some amount of incident power will be reflected back to the source in the practical system). Both these parameters are used to find a match between a source and load of a system.

The return loss & VSWR is related by the following formula, from which we can calculate return loss for a given VSWR.  

Where,

RL = Return loss in dB

VSWR = Voltage standing wave ratio