Article (edit | visual edit | history) · Article talk (edit | history) · Watch

Reviewer: Corvus coronoides (talk · contribs) 11:50, 4 August 2013 (UTC) Review in progress. Cheers, Corvus coronoides _talk 11:50, 4 August 2013 (UTC)[reply]

Thanks very much for reviewing Corvus. Not a very extensive article by my standards, but I thought it might still be up to GA standard. SpinningSpark 12:03, 4 August 2013 (UTC)[reply]

My pleasure. I've done my best, but I'm going to have to ask for a second opinion on this one. In the meantime, see below. Corvus coronoides _talk 13:13, 5 August 2013 (UTC)[reply]

This is a tricky article to review, given its inherently technical nature. My background is in aerospace engineering, rather than EE, so I'm reviewing from the perspective of an interested reader unfamiliar with the discipline. Some of the issues I am raising are therefore more like questions. Overall the article looks pretty good to me, but I feel the need to ask for a second opinion because this is my first review of a very technical article.

Prose — Mostly readable and correct, but I'm finding it somewhat inaccessible. Per WP:NOTTEXTBOOK, "Texts should be written for everyday readers, not for academics." Some work could be done to clarify the following points for a technically cognizant reader unfamiliar with the jargon of electrical engineering.

• "References to symmetry and antimetry of a network usually refer to the input impedances of a two-port network when correctly terminated." --> 1) What does it mean to be correctly terminated? This sentence needs clarification - if "correctly terminated" means "according to the definition presented below", there is probably a clearer way to say that. "Correctly terminated" makes me think "terminated in such a way that the circuit will not explode". 2) My background is in aero. eng. rather than EE, and the last related work I've done is intro E&M. That said, I don't know what "input impedances" are, and they're not defined. If every electrical engineer will know what you're talking about, just say so.

  I have added "glossary notes" to explain input impedance and termination impedance. These concepts would certainly be readily understood by electrical engineers and it is "bread and butter" in the fields of telecommunications, radio, and sound engineering. If you think it necessary we can try to work more of it into the body. SpinningSpark 15:54, 5 August 2013 (UTC)[reply]

  I think it is helpful to have those notes there, and no, I don't think they need to be in the body. Corvus coronoides _talk 03:31, 6 August 2013 (UTC)[reply]

• "A symmetric network will have the two equal impedances, Zi1 and Zi2." --> seems to imply that a symmetric network can only have two impedances, and they will be equal, whereas the figure at the right tells me that there are can be a ladder with many elements. If you mean a sort of equivalent impedance, can this be clarified?

  I have clarified this as "...two equal input impedances..." As explained in the note added above, the input impedance is the impedance looking into a port. It is quite separate from the impedances of the network branch elements (but dependent on them). The number of input impedances of a network is therefore equal to the number of network ports. This article is explicitly discussing two-port networks, thus the number of input impedances being considered is two. SpinningSpark 16:08, 5 August 2013 (UTC)[reply]

  Ah, I see. Corvus coronoides _talk 03:31, 6 August 2013 (UTC)[reply]

• "Symmetric and antimetric networks are often also topologically symmetric and antimetric, respectively. That is, the physical arrangement of their components and values are symmetric or antimetric as in the ladder example above." --> I get that a symmetric network need not be topologically symmetric. I am confused about how a network can be topologically antimetric (it seems to me that antimetry is not an established property of manifolds, and with my understanding of topology I don't believe the topology of a circuit can take into account the values of elements along it, but I admit my understanding is limited) -- do you mean that an antimetric network need not be topologically asymmetric?

  There seems to be several points in there, I will address them below one at a time. I have not done anything to the article yet as I am not at all sure that I have properly understand your difficulty.

  • I am confused about how a network can be topologically antimetric. A network is topologically antimetric if, for instance, an inductance connected in series to port 1 has a corresponding capacitance connected in parallel to port 2. Series inductance and parallel capacitance are duals of each other and dual impedance is how we are defining antimetry in this article. In general, to test if a network is physically symmetrical, cut it in half along the centre-line between the two ports, mirror reflect one half on a vertical axis, and if it is identical to the second half then it is symmetric. To test if a network is physically antimetrical, cut it in half along the centre-line between the two ports, mirror reflect one half on a vertical axis, transform it into its dual and if it is identical to the second half then it is antimetric. If any of that makes any sense and seems to be helpful we can see about putting it in the article.
  • I don't believe the topology of a circuit can take into account the values of elements. Yes, strictly speaking different values do not amount to different topologies. However, it is still a requirement of (physical) symmetry/antimetry that the values are identical/dual.

  I believe I see what you're saying here. In that case, I do think it is important to say in section 2 that an antimetric network needs not be either physically or topologically symmetric.Corvus coronoides _talk 03:31, 6 August 2013 (UTC)[reply]

  I think you meant to say ...or topologically antimetric. Not really, if a network is not topologically antimetric then it is automatically precluded from being physically antimetric - topology is part of the physical layout. I have reworded slightly so that it is not implied that component values form part of topology. SpinningSpark 13:38, 6 August 2013 (UTC)[reply]

  • do you mean that an antimetric network need not be topologically asymmetric? No, an antimetric network is asymmetric.

  SpinningSpark 17:47, 5 August 2013 (UTC)[reply]

• " For example, if the example networks from the preceding section have an additional T-section added to the left-hand side, then the networks remain topologically symmetric and antimetric. However, the network resulting from the application of Bartlett's bisection theorem[3] applied to the first T-section in each network are neither physically symmetric nor antimetric but retain their electrical symmetric (in the first case) and antimetric (in the second case) properties." --> based on my click-through to T-section, it seems to me that adding a T section requires adding two circuit elements to the left-hand side, and depending on the values chosen for the impedances, one could make the networks neither electrically symmetric nor electrically antimetric. Further, it seems that the paragraph uses the terms "physical symmetry/antimetry" and "topological symmetry/antimetry" interchangeably - if they are not the same, this should be clarified. If they are the same, it seems that adding the T-section as suggested would make both networks physically symmetric.

  • a T section requires adding two circuit elements Don't know where you got that idea from. A T-section consists of three elements, as is clearly shown on File:Filter topologies.svg and the first diagram of this article.

  My bad. I figured if you added a T section you'd add the two impedances coming from the right branch of the top T... never mind. I get it. Corvus coronoides _talk 03:31, 6 August 2013 (UTC)[reply]

  • depending on the values chosen for the impedances, one could make the networks neither electrically symmetric nor electrically antimetric. True, clarified with "identical T-section".
  • uses the terms "physical symmetry/antimetry" and "topological symmetry/antimetry" interchangeably They are not being used interchangeably, but all occurences of topological could probably be replaced with physical without loss of meaning. However, I like the article linking to Topology (electrical circuits) as this is quite helpful in explaining the concepts.

  I like the link to topology too. here's what I'm getting out of what you're saying. Why not use topological for all uses of physical?Corvus coronoides _talk 03:31, 6 August 2013 (UTC)[reply]

  Because topological does not include component values, which are part of antimetry so it might not be appropriate in all circumstances. SpinningSpark 13:38, 6 August 2013 (UTC)[reply]

  • It may make it clearer if an intermediate diagram was provided. That is, after the additional T-section has been added but before the Bartlett transformation is carried out. I had considered doing this, but frankly, the article would have ended up more diagrams than text. Let me know if you think that would be useful.

  SpinningSpark 18:23, 5 August 2013 (UTC)[reply]

  I don't have a problem with more diagram than text; it might not look nice but will be more informative. A picture is worth a thousand words.Corvus coronoides _talk 03:31, 6 August 2013 (UTC)[reply]

  Done SpinningSpark 09:55, 7 August 2013 (UTC)[reply]

Coverage — Article seems to provide an appropriate description of the topic, and detail level seems appropriate. Two questions that I will defer to the nominator's expertise:

• Article describes antimetry with respect to impedances and S-parameters -- are there other kinds of antimetry which are not discussed? I wouldn't fuss if there were one definition applicable to all, but the definitions with respect to impedance and with respect to S-parameters are not the same, so I want to check to see if there are missing definitions not covered.

  It is not a different kind of antimetry, it is just a different way of representing it. As far as I know, the s-parameter representation is completely equivalent. I don't know of any corner cases where they diverge. If you want a definitive answer to that question you might try user:Catslash who seems to know an awful lot about s-parameters. Antimetry could be defined in terms of other sets of two-port parameters. For some, z-parameters for instance, the relationship is simple and obvious. For others, h-parameters for instance, the formulae would be somewhat more complicated. I have singled out the s-parameters because unlike most of the other parameters described in the article, the s-parameters are not based on measurements of voltage and current (that, and there was a source to hand). This becomes important at microwave wavelengths where voltage and current are impratical to measure and at optical wavelengths impossible. However, power is readily measured and s-parameters are defined in those terms. SpinningSpark 18:55, 5 August 2013 (UTC)[reply]

  Well, two points: a) I think the sentence "Other network parameters may also be referred to as antimetric." makes it sound like you can define antimetry with respect to different parameters in the same way that you could define orthogonality with respect to different inner products, if that makes sense. It's not immediately obvious to me that S-parameter antimetry is equivalent, so I think it's worth explicitly stating. b) one of the GA criteria is addressing main aspects of the topic. If the impedance definition is overwhelmingly the most common definition, then I think the article is fine as is. If it is also common to define antimetry in terms of these other parameters, I think it becomes a case where the article has holes in its coverage. You tell me which it is. Corvus coronoides _talk 03:31, 6 August 2013 (UTC)[reply]

  I have moved the two-port parameter discussion to its own section, made it clear that this is not a separate definition (just another representation), expanded, and included z-parameters. SpinningSpark 11:13, 7 August 2013 (UTC)[reply]

• Is there anything special about an antimetric electrical network? Does it have special applications or special properties, whether physical or mathematical?

  The physical and mathematical properties are what they are. I have added something about Butterworth filters by way of an example. SpinningSpark 07:32, 6 August 2013 (UTC)[reply]

Images — No copyright violations here, but I have some suggestions to clarify the illustrations:

• Humor me and tell me in the first image, what is considered an "input impedance" in the network shown? What is the resistance R_0 with respect to which the impedances are the duals of each other? Is this expected to be general knowledge to someone in this field?

  Hopefully, these concepts are now explained a little better in the article.

  • The input impedance is not a physical component. It is the impedance "looking into" the port in question.
  • R₀ is also not a physical component. In terms of the theory it is merely an arbitrary constant, often set to unity to simplify calcualtions (all components can later be scaled to the actual required values using the procedure explained in prototype filter). All EEs will automatically read Z₀ as characteristic impedance and hence R₀ as characteristic resistance. We just need to say it is a nominal value here in this article. However, in a real design, the circuit will expect to be terminated in the nominal impedance and the designer will strive to make the input impedance match it, at least approximately within the passband (few circuits, including the examples in this article, are capable of presenting a truly constant and resistive impedance). Often, the nominal impedance will be chosen to match the characteristic impedance of the cables used (an almost universal standard is 50 ohms for RF and 75 ohms for video). Something can be said on all this, but frankly, these are general considerations of circuit design, not especially relevant to Antimetric networks and are best left to other, more appropriate, articles. SpinningSpark 20:17, 5 August 2013 (UTC)[reply]

  oh so what I meant was, in the image example caption, could you tell me what the value of R_0 is in terms of L and C? I didn't mean that it was a physical component; I just thought it might help the uninitiated reader understand if the sentence read something like "the network on the right is antimetric with respect to R_0 = f(L,C)". Corvus coronoides _talk 03:31, 6 August 2013 (UTC)[reply]

  I don't think that would be a good idea. Although the article does not say so, the example circuits are image parameter filter designs. In this design R₀ = √ (L/C). I chose this design because it commonly uses simple symmetric and antimetric designs which are good for examples. However, modern filter design techniques are more complex and mathematical and that equation would be meaningless and/or misleading. The most generally applicable and relevant thing to say in relation to this article is that R₀ is chosen to equal the terminating impedances. How terminating impedance relates to network component values is an issue for individual designs of network, not for the property of antimetry. SpinningSpark 11:40, 7 August 2013 (UTC)[reply]

  Ah I see. That's a good point. Corvus coronoides _talk 17:55, 7 August 2013 (UTC)[reply]

• First image caption: seems to contain a more general definition of antimetry than that given in the prose. I believe the prose should always contain the more general definition and an image ought to illustrate either the general case if possible, or a specific case.

  I don't think that is exactly right. The prose has the general and exact definition. The definition in the image caption is specific to ladder networks. But see an earlier comment where I floated possible alternative/additional descriptions that could be added. SpinningSpark 20:34, 5 August 2013 (UTC)[reply]

  I see. Corvus coronoides _talk 03:31, 6 August 2013 (UTC)[reply]

The above represents some points where the article could be improved. I am going to ask for a second opinion on the GA status of this article simply because I have never reviewed an article with this kind of technical nature before. Best, Corvus coronoides _talk 13:13, 5 August 2013 (UTC)[reply]

Hi there. I was fortunate to have some expeditious responses when I requested a second opinion here. One point raised by User:Andy Dingley is that the concept of a transfer function may merit discussion. I am thinking that this may (or may not) fall under the area of "special properties" of antimetric networks alluded to above. If not, please say so. I am hoping that Andy will elaborate on his comments here, as well. Corvus coronoides _talk 14:12, 5 August 2013 (UTC)[reply]

Transfer function is certainly an important concept, but it is hard to see what Andy expects this article to say about it. The two concepts do not really intersect; one can design, for instance, a low-pass filter with either a symmetric, or an antimetric topology. They still both have low-pass filter transfer functions. The transfer function depends on the number, type and configuration of elements used, but not directly on symmetry. The most that could be said, taking the LPF ladder in the article as an example, is the rather trivial observation that a symmetrical ladder must have an odd number of elements and an antimetrical ladder must have an even number of elements. The corresponding transfer functions thus have odd and even orders respectively.

I agree with Andy's comment that EEs would always say "S-paramater", but the title of our article is actually scattering parameters. On the principle of least astonishment that is what I have linked. I am happy if Andy wants to change it, but then I am an EE and already understand it. SpinningSpark 16:43, 5 August 2013 (UTC)[reply]

Your answer regarding the transfer function is pretty much what I had surmised. Corvus coronoides _talk 03:31, 6 August 2013 (UTC)[reply]

Thanks for the review Corvus. If you don't object, I will reply to your comments immediately after each point to save having to repeat them. SpinningSpark 15:09, 5 August 2013 (UTC)[reply]

No objection at all. See replies in-line above. Also, I am going to consider this article on hold now. You've answered most of my questions; I just have a few remaining suggestions. Corvus coronoides _talk 03:31, 6 August 2013 (UTC)[reply]

I believe I have now responded to all points raised. Is there anything else? SpinningSpark 11:45, 7 August 2013 (UTC)[reply]

Looks good. I have one nitpicky comment at this point - regarding the section title "Two-port parameters". I am thinking that it may be a more informative title if it were something like "Definition in terms of two-port parameters" or "Other formulations of antimetry conditions" or something like that. The title Two-port parameters makes me think it's going to be a list of two-port parameters in some ways. Corvus coronoides _talk 17:55, 7 August 2013 (UTC)[reply]

The whole point of this change was to make it clear that these were not alternative definitions. We don't now want to be go saying that they are. We could have "Effect on two-port parameters". SpinningSpark 18:25, 7 August 2013 (UTC)[reply]

Yes, I see what you're saying. Well, it may be unavoidable in the section title. If readers read the text it should be fine, I think. Corvus coronoides _talk 18:34, 7 August 2013 (UTC)[reply]

GA review (see here for what the criteria are, and here for what they are not)

Good work on a technical subject.

1. It is reasonably well written.

   a (prose, no copyvios, spelling and grammar): b (MoS for lead, layout, word choice, fiction, and lists):

   Prose is clear enough, math is inserted where appropriate. I believe this article is accessible to the technically cognizant reader not necessarily in the field of EE.

2. It is factually accurate and verifiable.

   a (reference section): b (citations to reliable sources): c (OR):

   adheres to standards for citations in scientific articles, and links to related concepts.

3. It is broad in its coverage.

   a (major aspects): b (focused):

   defines antimetry, gives examples, and discusses practical examples. Detail not excessive.

4. It follows the neutral point of view policy.

   Fair representation without bias:

   Not an issue.

5. It is stable.

   No edit wars, etc.:

   No edit wars here.

6. It is illustrated by images and other media, where possible and appropriate.

   a (images are tagged and non-free content have fair use rationales): b (appropriate use with suitable captions):

   Images created by nominator and licensed appropriately. Captions good.

7. Overall:

   Pass/Fail:

   Thanks for bearing with me as I attempted to sort through the unfamiliar technical details. Corvus coronoides _talk 18:34, 7 August 2013 (UTC)[reply]

   No, thank you for taking the trouble to review. SpinningSpark 18:53, 7 August 2013 (UTC)[reply]