The meaning of the term Return Loss

There are so many instructional / tutorial videos on the ‘net, and Smith charts are the subject of lots.

But can you trust what you read / see online?

Here an author gives his take on Return Loss.

Errr, no!

Using his terms, \(Return\_Loss=\frac{P_{sent}}{P_{return}}\), a result greater than unity, or we can express it in dB (not db, the B is for Bell, a person’s name, so it must be capitalised in the unit) \(Return\_Loss\_dB=10 log_{10}\frac{P_{sent}}{P_{return}}\) which will yield a positive dB value.

If we use a VNA and it reports the magnitude of S11, we can calculate \(Return\_Loss\_dB=-20 log_{10} |S11|= -S11\_dB\).

So it is quite wrong to speak of, or worse to label a plot of S11_dB as Return_Loss.

But “everybody does it, it must be right”! No, but it is true that on social media, popularity is taken to determine fact.