Talk:Scattering parameters

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Contents 1 Merge s-parameters into scattering parameters 1.1 Why I have merged s-parameters into scattering parameters 2 Renormalized/General 3 Spatial/temporal phase 4 math improvements, shortening 5 Lossy/Lossless networks 6 Agilent link

[edit] Merge s-parameters into scattering parameters

The page titled "s parameters" should probably be merged into this one.

I have just added quite a bit more from some of the classic references especially Pozar and Gonzalez and the infamous Agilent application notes. I hope this is a good start, the problem being avoiding rambling on for too long. Definitely should be merged with s parameters because this is just an abbreviation of the correct full descriptionChrisAngove 21:58, 11 April 2006 (UTC)

I have just added a few corrections and improvements. In a few days I plan to merge s-parameters into this one. Nobody has objected and I consider s-parameters to be more shall we say blog style than encyclopedic style.ChrisAngove 22:40, 19 August 2006 (UTC)

[edit] Why I have merged s-parameters into scattering parameters

They are of course the same subject. People less familiar with RF engineering often ask what the S stands for so the better title is the full name with redirection from s-parameters. I have read S-parameters and added a few things I had overlooked in scattering parameters. Now please can we have some more comments from the huge numbers of electrical/RF engineers who must surely read this. ChrisAngove 20:39, 19 September 2006 (UTC)

The merge was a good idea. Needed to be done. --Thesilmarilion 18:38, 26 October 2006 (UTC)

[edit] Renormalized/General

Nice article! - but I believe that what you describe as The General S-Parameter Matrix is usually called the Renormalized S-Matrix or Normalized-to-50Ω S-Matrix. The Generalized S-Matrix is for a matched load (as opposed to 50Ω) on each port (so that in A = SB, B is the amplitude of the in-going waves, and A is the amplitude of the scattered-out waves). I expect plain S-matrix could mean either normalized or not depending on whether the context was circuits or microwave devices. --catslash 09:50, 21 September 2006 (UTC)

I'm not following what you mean by I expect plain S-matrix could mean either normalized or not since S-parameters are always normalised to the port impedance. It's just that the port impedance is not always 50Ω.

It's also worth pointing out that each port impedance could be different such as is the case for a matching network. As a result referring to system impedance is only relevant for systems where all the port impedances are the same. --Thesilmarilion 18:12, 26 October 2006 (UTC)

Yes, it was the reference to system impedance that I was pointing out. Considering (say) a 50Ω to 25Ω quarter-wave transformer in microstrip, I would define the s-matrix with matched ports, so that when it was working properly, I would have s11 = s22 = 0 and |s12| = |s21| = 1. However (awkward and annoying) people tell me that they must have the s-parameters normalized to a single system impedance (i.e. the scattering between a source and load of the same impedance (e.g. 50Ω) on each port). The reasons given are (1) they want the s-parameters as input to a circuit simulator, which requires this, and (2) they want Touchstone format, which requires this. Hence the reference to system impedance made me suppose that the article was limited to renormalized s-parameters. --catslash 22:33, 26 October 2006 (UTC)

Thanks for the clarification. I think it would be worthwhile then to point out in the article that S-parameters may be normalised to any arbitrary impedance at any port with zero and infinity being the only exclusions but that there are some simulators out there that insist on requiring the specification of a system impedance where all ports are normalised to the same impedance. --Thesilmarilion 15:53, 27 October 2006 (UTC)

[edit] Spatial/temporal phase

I think it would be useful to explain the difference between 'spatial' and 'temporal' phases in the General S-Parameter Matrix section. As the text stands at present the terms are used without explanation or reference. --Thesilmarilion 18:13, 26 October 2006 (UTC)

Yes I agree with that. It seems like magic that you can just forget about the e^jωt so easily.ChrisAngove 20:23, 1 December 2006 (UTC)

I think what is missing is to note that the *relative* difference in phase between two ports remains constant over time. Or, we could equivalently say that the phase change was measured simultaneously at both ports. It may be misleading to differentiate between spatial and temporal phase - after all, a single frequency has only one phase. A phasor expression for a wave propagating in the z direction is e^{j(ωt − βz)}, where β is the phase constant, and this shows how the phase varies in both space and time. How about rewording the sentence to something like the following?

The phase part of the s-parameter tells the amount of phase change on one port relative to another for a given frequency. -Peter 129.237.165.40 06:00, 11 January 2007 (UTC)

[edit] math improvements, shortening

I have forced png rendering in the math tags using the \, characters to make the equations consistent. Also started to shorten sentences as the article is apparently somewhat long. May be possible to split it to say a definition and a measurement article.ChrisAngove 16:28, 1 January 2007 (UTC)

I agree that isolating a topic such as "S-parameter measurements" from "S-parameter definitions" would be useful. Thesilmarilion 13:54, 3 January 2007 (UTC)

[edit] Lossy/Lossless networks

In the text was used, this is valid in most cases, since for a lossless reciprocal network S_i,j = S_j,i. However to be correct, the following should be used , where {}^H indicates the hermetian matrix (complex conjugate transpose). This way it will also be valid for non-reciprocal network, like circulators. Btw: The hermetian should be the first term. Erik, 212.187.90.11 20:36, 19 February 2007 (UTC)

[edit] Agilent link

I added the Agilent link at the bottom of the page as a hyper-ref in good faith. It's a commercial site, but the application note is general and well written. I think I'm missing something about Wikipedia's linking policy, but why was it removed as spam? Surely a link just saves a Google search? Thanks, Arthurtech 14:22, 5 May 2007 (UTC) (aka 86.21.13.156).