Return Loss to VSWR Conversion Table

Return Loss

Definition ：Return Loss (RL) refers to the ratio of the power reflected back by an RF input signal to the power of the input signal.

As we all know, In the ideal source case, the antenna matches the impedance of the RF circuit exactly, and there is no reflected power at all. However, in the actual situation, the impedance cannot be completely matched, so the reflected power must exist.

So a large loss on the return “echo” is good. Smaller return loss is bad, and means less energy is going into our antenna. RF engineers often measure return loss on a “dB” logarithmic scale, which can make it seem more complicated than it really is.

For example, in the picture as below, due to the antenna impedance is 80Ω， and the feeder impedance is 50Ω， so the Return Loss is 10log(10/0.5)=13dB

VSWR

Definition ：Voltage Standing Wave Ratio (VSWR) is short for voltage standing wave ratio, which refers to the ratio of reflected wave amplitude to incident wave amplitude. When the impedance is ideally perfectly matched, the value of the standing wave ratio is 1.

For example, when RL=20Db ,VSWR=(1+0.1)/(1-0.1)=1.22