Why S - Parameter at High frequencies?
 

Owen Duffy wrote:
So, what you are referring to with the term "virtual reflection
coefficient" is the magnitude the reflection coefficient (rho). or |(Z02-
Z01)/(Z02+Z01)| (Gamma).

I believe the following web page is indicative of
how Gamma has essentially been replaced by rho.

http://www.ac6la.com/stss.html

The ARRL Antenna Book implies that rho is used
by amateur radio operators while Gamma is still
used in some professional circles.
--
73, Cecil http://www.w5dxp.com

Why S - Parameter at High frequencies?
 

The ARRL Antenna Book implies that rho is used
by amateur radio operators while Gamma is still
used in some professional circles.
--

As far as I'm concerned, Gamma is the complex reflection coefficient;
rho is its magnitude.

Why S - Parameter at High frequencies?
 

Wes wrote:
The ARRL Antenna Book implies that rho is used
by amateur radio operators while Gamma is still
used in some professional circles.

As far as I'm concerned, Gamma is the complex reflection coefficient;
rho is its magnitude.

That works as long as everyone else understands what you
are talking about. Here's a quote from:

http://www.ac6la.com/stss.html

"The SWR meter is only concerned with the magnitude of the
reflection coefficient, but rho is a complex quantity having
both a magnitude and angle. If rho were to be measured at
various points along a transmission line, the magnitude would
be fairly constant but the angle would change depending on
the electrical length of the line at the point of measurement."

And from the "ARRL Antenna Book":

"In some professional literature, Gamma is used in place of rho
to represent the reflection coefficient."

Wes, you must be a professional. :-)
--
73, Cecil http://www.w5dxp.com

Why S - Parameter at High frequencies?
 

On Apr 12, 6:39 am, "Wes" wrote:

As far as I'm concerned, Gamma is the complex reflection coefficient;
rho is its magnitude.

As far as I'm concerned, S11 = (Z-Zo)/(Z+Zo), and is commonly known as
the (port 1) reflection coefficient, and Zo = 50+j0 unless otherwise
specified -- and |S11| is the magnitude of that reflection
coefficient. If I see rho without a definition, I only have its
context to go by, and in some circles that's pretty weak and often
inaccurate. For other ports of a multiport network, of course, S22,
S33, and so forth serve.

Almost all I need to know about a TEM line can be expressed by the set
of 2-port S parameters versus frequency for the line. Normal coaxial
and open-wire lines come about as close as anything I work with to
being true linear systems. However, the two-port model covers only
the differential TEM propagation on the line, not the line versus
ground: it's not useful for analyzing the "antenna" currents on a
line. It also doesn't tell me whether lost power is lost to heating
or to radiation, and it doesn't tell me about radiation received by
the line. The S parameter set for the line can be referenced to 50
ohms (or any other useful impedance), independent of the impedance of
the line. With the S parameter set, I can determine power loss, power
transmission, images, ... all the usual things. Of course, it's not
the only way to characterize the line, but it's complete and accurate
to the extent the line really does behave linearly and that only the
TEM propagation is important. The line doesn't even have to be
uniform; it can be exponentially expanding, or have ripples in its
impedance. If the line isn't uniform, the S parameters won't be able
to tell you power dissipation versus distance along the line, but
they'll still give you net power dissipation under specified
conditions of excitation and load.

Cheers,
Tom

Why S - Parameter at High frequencies?
 

"Wes" wrote in news:1176385196.714553.293960
@y5g2000hsa.googlegroups.com:



The ARRL Antenna Book implies that rho is used
by amateur radio operators while Gamma is still
used in some professional circles.
--

As far as I'm concerned, Gamma is the complex reflection coefficient;
rho is its magnitude.

Hi Wes,

My preferred usage is the same, and for the reason that Gamma and rho can
be written directly in html as the greek symbols, and in ascii text as
Gamma and rho. The notation that rho is the magnitude of the complex
reflection coefficient and that the complex reflection coefficient is
written as rho with a bar over it is not conveniently and consistently
expressed in a short notation in ascii only media.

If it is declared (as I did in my post) then the usage is fair. The
sidetrack onto "standard" notation was just another diversionary tactic
from YKW.

Owen

Glossary:
YKW - You Know Who

Why S - Parameter at High frequencies?
 

This topic has been discussed in this newsgroup several times in the
past. In my posting of June 17, 2005 in the thread " Calculating VSWR
from rho and rho from VSWR" you'll find a summary of what I found in use
by authors of 16 different textbooks. As you'll see, if you look it up
at http://groups.google.com, there's no single standard usage.

Personally, my preference is the same as Wes' and Owen's - Gamma for
complex reflection coefficient, rho for its magnitude. But usage is so
varied that it's necessary to explicitly show what the symbols mean
unless it's obvious from the context.

Roy Lewallen, W7EL

Owen Duffy wrote:
"Wes" wrote in news:1176385196.714553.293960
@y5g2000hsa.googlegroups.com:

The ARRL Antenna Book implies that rho is used
by amateur radio operators while Gamma is still
used in some professional circles.
--
As far as I'm concerned, Gamma is the complex reflection coefficient;
rho is its magnitude.

Hi Wes,

My preferred usage is the same, and for the reason that Gamma and rho can
be written directly in html as the greek symbols, and in ascii text as
Gamma and rho. The notation that rho is the magnitude of the complex
reflection coefficient and that the complex reflection coefficient is
written as rho with a bar over it is not conveniently and consistently
expressed in a short notation in ascii only media.

If it is declared (as I did in my post) then the usage is fair. The
sidetrack onto "standard" notation was just another diversionary tactic
from YKW.

Owen

Glossary:
YKW - You Know Who

Why S - Parameter at High frequencies?
 

On Apr 12, 2:04 pm, Roy Lewallen wrote:
This topic has been discussed in this newsgroup several times in the
past. In my posting of June 17, 2005 in the thread " Calculating VSWR
from rho and rho from VSWR" you'll find a summary of what I found in use
by authors of 16 different textbooks. As you'll see, if you look it up
athttp://groups.google.com, there's no single standard usage.

Personally, my preference is the same as Wes' and Owen's - Gamma for
complex reflection coefficient, rho for its magnitude. But usage is so
varied that it's necessary to explicitly show what the symbols mean
unless it's obvious from the context.


In my response in the thread "Question about reflection/transmission
coefficients", April 28, 2003 I had only 10 different references.

Why S - Parameter at High frequencies?
 

Wes wrote:
On Apr 12, 2:04 pm, Roy Lewallen wrote:
This topic has been discussed in this newsgroup several times in the
past. In my posting of June 17, 2005 in the thread " Calculating VSWR
from rho and rho from VSWR" you'll find a summary of what I found in use
by authors of 16 different textbooks. As you'll see, if you look it up
athttp://groups.google.com, there's no single standard usage.

Personally, my preference is the same as Wes' and Owen's - Gamma for
complex reflection coefficient, rho for its magnitude. But usage is so
varied that it's necessary to explicitly show what the symbols mean
unless it's obvious from the context.


In my response in the thread "Question about reflection/transmission
coefficients", April 28, 2003 I had only 10 different references.

Well, then, it's your turn again, Wes, and right on the biannual
schedule. Should it be 22 references (arithmetic increase) or 26
(exponential) this time?

Roy Lewallen, W7EL

Why S - Parameter at High frequencies?
 

On Apr 10, 4:21 am, "ilam" wrote:
I am in a process of understanding the importance of S-Parameter at
high frequencies, please answer my following questions:

1. Why Measuring a wave (voltage or current) is more easier than
volage and current? ( Why measuring S-Parameter is more easier than
other parameters?)

2. How the voltage and current waves are measured?

Measuring voltage and current are difficult at high frequncies, that
is why S-Parameter is more useful at high frequncies. Is the same
thing is true for simulation?

Regards,
Ilam

Search the agilent website for the original application note on S-
parameters.. it provides a great explanation of why S-parameters are
used.

You've correctly assessed the situation.. at microwave frequencies,
it's much easier to measure forward and reflected signals (and
calibrate for non-ideal directional couplers, etc.) than to measure
voltage and/or current.

Why S - Parameter at High frequencies?
 

Cecil Moore wrote:
Owen Duffy wrote:

So, what you are referring to with the term "virtual reflection
coefficient" is the magnitude the reflection coefficient (rho). or |(Z02-
Z01)/(Z02+Z01)| (Gamma).


I believe the following web page is indicative of
how Gamma has essentially been replaced by rho.

http://www.ac6la.com/stss.html

The ARRL Antenna Book implies that rho is used
by amateur radio operators while Gamma is still
used in some professional circles.

"still used"... I don't know that expressing reflection coefficient as
gamma is an archaic notation. You see it a lot in performance
specifications for RF test equipment like network analyzers. Where the
magnitude is meant (and Gamma isn't real) you'd see it written with
vertical bars on either side ||.

For instance, in the latest Agilent PNA manuals, they use capital Gamma.

here's an interesting interactive smith chart
http://www-ece.eng.uab.edu/JCaldwel/...art/SChart.htm


lower case gamma is used for the complex propagation constant in
transmission lines.