Could some electronics guru here please clarify this ? Since my engineering school days, I have been told that the return loss(e.g., for an antenna) is RL = -20.0log(|gamma|) where gamma is the reflection coefficient.However, recently I have come across journal articles, papers where the authors use: RL = 20.0log(|gamma|), i,e,, the negative sign is missing. Which of these two is correct ?
ng school days, I have been told that the return loss(e.g., for an antenna ) is
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ese two is correct ?
This almost funny. You should be able to work that out for yourself. Do you worry about the sign of the loss of attenuators too?
Jeroen Belleman
Neither antennas nor attenuators usually return more power than you send them. I suppose their return loss is positive and their return gain is negative.
-- John Larkin Highland Technology, Inc Science teaches us to doubt. Claude Bernard
The one with the minus sign is the return loss, the one without is the return gain. In a passive system, the loss in dB is positive, while the gain in dB is negative.
Unless you're building reflection amplifiers, no confusion is likely to result.
Cheers
Phil Hobbs
-- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC / Hobbs ElectroOptics Optics, Electro-optics, Photonics, Analog Electronics Briarcliff Manor NY 10510 http://electrooptical.net http://hobbs-eo.com
Wiki says that return loss of a lossy device is positive in dB.
Tunnel diode RF amps needed a circulator to separate the input from the output.
-- John Larkin Highland Technology, Inc Science teaches us to doubt. Claude Bernard
I disagree, Phil. I think you have them backwards.
gamma magnitude (can be a complex number) is less than 1 so logarithm is negative, meaning you want to add a negative sign to make it a positive loss number. All logs cross thru zero at 1 and nosedive to -oo at 0.
A negative gain is a positive loss. A negative loss is a positive gain. OMG- semantics!
A really well matched system might have a return loss of (plus) 30 dB. No?
Cheers
Phil Hobbs
-- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC / Hobbs ElectroOptics Optics, Electro-optics, Photonics, Analog Electronics Briarcliff Manor NY 10510 http://electrooptical.net http://hobbs-eo.com A
Well then we agree. I feel so validated. ;)
Cheers
Phil Hobbs
-- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC / Hobbs ElectroOptics Optics, Electro-optics, Photonics, Analog Electronics Briarcliff Manor NY 10510 http://electrooptical.net http://hobbs-eo.com
Yes. I misread your statement. Sorry.
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