Return Loss to VSWR Calculator

What is return loss?

Impedance mismatch/discontinuity between the transmission line/cable to the connected load/component results in a standing wave pattern along the transmission line, by which a small amount of incident signal power reflects 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, so high return loss is desirable for a system. VSWR means that the ratio of the maximum voltage to the minimum voltage in the standing wave pattern along the transmission line.

Understanding return loss

How to relate the return loss and VSWR?

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 no 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 always a small impedance mismatch. Hence, the return loss is always lower than the ideal system (i.e., some amount of incident power will reflect the source in a practical system).

The following formula relates the return loss and VSWR. This formula is used to calculate the VSWR from the given return loss.

Where,

RL = Return loss in dB

VSWR = Voltage standing wave ratio.