Question regarding return loss formula...

A

amal banerjee

Guest
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 ?
 
lørdag den 19. september 2020 kl. 11.49.43 UTC+2 skrev amal banerjee:
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 ?
Click to expand...

https://en.wikipedia.org/wiki/Return_loss#Sign
 
On 2020-09-19 11:49, amal banerjee wrote:
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 ?
Click to expand...

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
 
On Sat, 19 Sep 2020 14:16:41 +0200, Jeroen Belleman
<jeroen@nospam.please> wrote:

On 2020-09-19 11:49, amal banerjee wrote:
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 ?


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
Click to expand...

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
 
On 2020-09-19 05:49, amal banerjee wrote:
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 ?
Click to expand...

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
 
On Sat, 19 Sep 2020 11:36:41 -0400, Phil Hobbs
<pcdhSpamMeSenseless@electrooptical.net> wrote:

On 2020-09-19 05:49, amal banerjee wrote:
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 ?


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
Click to expand...

Wiki says that return loss of a lossy device is positive in dB.

https://en.wikipedia.org/wiki/Scattering_parameters#Input_return_loss

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
 
On 9/19/2020 10:36 AM, Phil Hobbs wrote:
On 2020-09-19 05:49, amal banerjee wrote:
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 ?


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
Click to expand...

I disagree, Phil. I think you have them backwards.
 
On Saturday, September 19, 2020 at 5:49:43 AM UTC-4, daku...@gmail.com wrote:
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 ?
Click to expand...

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.
 
On Saturday, September 19, 2020 at 1:03:38 PM UTC-4, jla...@highlandsniptechnology.com wrote:
On Sat, 19 Sep 2020 11:36:41 -0400, Phil Hobbs
pcdhSpamM...@electrooptical.net> wrote:

On 2020-09-19 05:49, amal banerjee wrote:
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 ?


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
Wiki says that return loss of a lossy device is positive in dB.

https://en.wikipedia.org/wiki/Scattering_parameters#Input_return_loss

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
Click to expand...

A negative gain is a positive loss. A negative loss is a positive gain. OMG- semantics!
 
On 2020-09-19 15:31, John S wrote:
On 9/19/2020 10:36 AM, Phil Hobbs wrote:
On 2020-09-19 05:49, amal banerjee wrote:
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 ?


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


I disagree, Phil. I think you have them backwards.
Click to expand...

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
 
On 2020-09-19 13:03, jlarkin@highlandsniptechnology.com wrote:
On Sat, 19 Sep 2020 11:36:41 -0400, Phil Hobbs
pcdhSpamMeSenseless@electrooptical.net> wrote:

On 2020-09-19 05:49, amal banerjee wrote:
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 ?


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.
s

Wiki says that return loss of a lossy device is positive in dB.
Click to expand...

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
 
On 9/19/2020 8:56 PM, Phil Hobbs wrote:
On 2020-09-19 15:31, John S wrote:
On 9/19/2020 10:36 AM, Phil Hobbs wrote:
On 2020-09-19 05:49, amal banerjee wrote:
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 ?


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


I disagree, Phil. I think you have them backwards.

A really well matched system might have a return loss of (plus) 30 dB.  No?

Cheers

Phil Hobbs
Click to expand...

Yes. I misread your statement. Sorry.
 
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