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#11
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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 I believe the following web page is indicative of how Gamma has essentially been replaced by rho.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 |
#12
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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. |
#13
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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 |
#14
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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 |
#15
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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 |
#16
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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 |
#17
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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. |
#18
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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 |
#19
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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. |
#20
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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. |
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