I am having a hard time finding a good definition of return loss ratio. They all use the ratio of the incident wave at the antenna to the reflected wave, but some are Pi - Pr and others are Pr - Pi. Reported values for the ratio in dB are all positive... except for the ones that are negative.
WTF!!!
There is even an IEEE paper on this in "IEEE Antennas & Propagation Magazine", but it is subscription and I'm not willing to pay $100 for this little gem of knowledge.
I have one reference which gives an equation for system loss
Ls = 10 log (pt/pa) = Pt - Pa, dB
where Ls is the loss in decibels, pt is the power delivered to the antenna terminals, pa is the power at the receiving antenna.
The equivalent equation for the return loss at the transmitting antenna would be
Lr = 10 log (pt/(pt-pr))
where pr is the power reflected. The equations I found for return loss are
Lr = 10 log (pt/pr)
and
Lr = 10 log (pr/pt)
Anyone know what is going on?