Return Loss Ratio

Den mandag den 28. september 2015 kl. 19.55.07 UTC+2 skrev rickman:

if you can give a the full name of the paper, I can check it out, I probably have access

-Lasse

Definition and Misuse of Return Loss [Report of the Transactions Editor-in-Chief]

This will be greatly appreciated.

In theory, if the reflected signal is less than the incident signal the value should be positive (because it is called a loss).

The issue is that people often store the incident level as a reference in the power meter and then read the reflected power using the differential mode. That shows a negative value. They then forget to remove the minus sign.

Bob

I sent it, it is only 2 pages

-Lasse

Return loss is

RL = -20log10|Gamma| dB

Gamma := reflection coefficient

Gamma is a ratio.

Gamma = Vo-/Vo+ = (ZL-Zo)/(ZL+Zo) (relected voltage wave over the inci dent voltage wave.)

Pi = |Vo+|^2/(2Zo) Pr = |Vo-|^2/(2Zo)

As seen, the i & r voltage waves are related to i & r powers, of course.

The reason for negative return loss is usually a mistake. That usually sho uld be called "return gain." To say *loss* is positive is to say there is actual loss. Negative loss is actual gain. Some people get pissy when you point out the mistake in sign. If all other ports are terminated in their characteristic impedance, and you have an actual negative return loss, that means more power is available from the port than what you put in. You'd h ave a way to make an oscillator. It implies an "internal" energy source.

The expression on the far right is obviously wrong.

re

PL is power delivered to the load GammaL is the reflection coefficient of the load

PL = Pi - Pr = Pi(1 - |GammaL|^2)

so

Pr/Pi = |GammaL|^2

|GammaL| = sqrt(Pr/Pi)

RL = -20log|GammaL| = -20log(sqrt(Pr/Pi)) = -10log(Pr/Pi)

Thanks. I've already shared some quotes from it.