# What is Return Loss?

Return loss is a measure of the amount of signal that is reflected back to the source in a communication system, typically in the context of radio frequency (RF) and microwave systems.

## Background

Return Loss is a way to quantify the efficiency of power transfer between the source and the load or the impedance mismatch in a transmission line or system.

In simple terms, return loss occurs when some of the signal sent from the source doesn’t get absorbed by the load (receiver) but instead bounces back towards the source. This can happen when there is an impedance mismatch between the source and the load, which can lead to signal reflections.

## Formula

Referring to the picture of a two port network shown below, a1 and b1 are the incident and reflected power from a two-port network.

If a1, b1 are linear numbers,

Return Loss = 10*Log10(a1/b1)

Return Loss is usually expressed in decibels (dB). It is a ratio between two power levels and therefore does not have any units.

Since b1 is less than or equal to a1, the logarithm is a positive quantity.

The higher the return loss in dB, the less signal is being reflected, which is generally desired in most communication systems in order to minimize signal loss and ensure efficient power transfer.

A higher value of return loss indicates a better match between the source and load impedance, reducing signal reflections and improving the overall performance and signal integrity of the system.

Conversely, a lower value return loss suggests a greater impedance mismatch and more signal reflections, which can lead to signal degradation and reduced performance.

Generally 15 dB or greater is considered a good value of return loss. At this level (using this mismatch loss calculator), only 3% of the incident power is reflected while 97% is transmitted forward.