Return loss sentence...

Hi. Is this sentence correct ?

Return loss is a measure of how well devices or lines are matched. A match is good if the return loss is high. A high return loss is undesirable and results in a lower insertion loss.

No. The last sentence should be: "A high return loss is desirable and results in a lower insertion loss."

Basically, RL is the measure of how much of your signal is NOT coming back to you and is therefore being passed to the next circuit. If your return losses are "high", that means that most of your signal is getting to the next stage.

I always thought that "return loss" was a screwy name to give something. Having a "loss" means (to me) that this is something that you DON'T want. However, in the case of RL, you want as much "loss" as you can get (for most situations).

Thanks. Agree with the screwy convoluted name. I suspected so; to me, the 'return loss' expression is how much a reflected signal is reduced. Desirable is that reduction being high.

I will edit/correct Wikipedia (the text source) after waiting a while for other replies/suggestions/expressions/definitions here.

Large/small can be confusing if S11 plots are labeled "return loss".

But that text that you quoted is inconsistent indeed, change to "desirable".

More important is to realize that low return loss is necessary for low insertion loss but it is not sufficient.

That is so true. A 50Ω, 10dB pad has fantastic return loss, but it's insertion loss is 10dB (by design).

S11 in this case will probably be -20 dB. Anyone know why?

The forward-traveling or incident signal is attenuated by the amount of attenuation of the pad, and then the reflected or reverse-traveling signal is attenuated by the amount of attenuation of the pad. So, the effect of the attenuation is doubled.
A 10dB pad attenuator will have -20dB return loss, a 6dB pad attenuator will have -12dB return loss, and so on...

This is valid ONLY if the load impedance is 50 ohms (for a 50 ohms inp/out terminated attenuator).

Question... If it is expressed this way, would it be right ?

...realize that low return is necessary for low insertion loss... ?

Or

...high return loss is necessary for low insertion loss... ?



?? Question... Should it be expressed instead :

...A 10dB pad attenuator will have 20dB return loss, a 6dB pad attenuator will have 12dB return loss, and so on... ?

That is only true if the other end of the attenuator is either shorted or open (infinite reflection). There are times when an atten is used between two 50Ω parts of a system, so the return loss will be high - a lot higher than 2xATTEN.