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Talk:Planar transmission line/GA1

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Latest comment: 6 years ago by Mike Christie in topic GA Review

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Reviewer: Mike Christie (talk · contribs) 23:59, 4 January 2018 (UTC)Reply

I'll review this. Mike Christie (talk - contribs - library) 23:59, 4 January 2018 (UTC)Reply

Just starting to look at this now. A couple of notes on the sources:

  • You cite Franco De Flaviis under F in the bibliography and under D when citing him (footnote 4); should be consistent.
  • The cites to Garg should make it apparent whether you're citing Garg 2001 or Garg 2013.
  • You have both "Russer" and "Ruisser".
  • Several works in the bibliography aren't cited; it looks as if most or all of them are by authors you mention in the text, so presumably they cover the material mentioned. Completely optional, but you might consider separating them into a "Further reading" section. The ones I think would be in that category are Barrett (both), Cohn, Connor, Grieg, King, Meier, Pengelly, Robertson, and Wen.
    • That's right, the uncited publications are largely (possibly entirely) the primary sources reporting the discovery of the discussed effect/device. These were not used directly as sources for the article, later secondary sources were used for that, but it is useful to include them for readers who want to look them up. I am not in favour of putting them in further reading; if was asked to recommend further reading for this subject I would not point anyone to the historic primary sources unless that was what was explicitly asked for. SpinningSpark 16:09, 8 January 2018 (UTC)Reply
      Fair enough. Mike Christie (talk - contribs - library) 21:17, 8 January 2018 (UTC)Reply

Other than that the sources and citations look fine.

I'll add notes below as I go through the article. Please revert any copyedits I make if I screw anything up. -- Mike Christie (talk - contribs - library) 20:35, 7 January 2018 (UTC)Reply

Mike, many thanks for reviewing this. SpinningSpark 16:09, 8 January 2018 (UTC)Reply

Just a reminder as I start posting notes that I am not at all knowledgeable in this area; I have some (decades-old) undergraduate physics, but my degree is in maths. I've read the article a couple of times, skimming to get the structure and basic sense, and have done some reading in the connected articles to try and bring myself up to speed. I don't think there's any point in an article like this in asking for definitions of elementary concepts, but I am not always going to be sure what counts as elementary.

  • What's the asterisk for on "coplanar waveguide" in the lead? Is it just a typo? Is it intended to be replaced by the disconnected "[A]" at the foot of the lead?
    The footnote which is the target of the [A] is indeed intended to be the target of the *. [This edit] broke it. The edit could be fixed, but Spinningspark may prefer simply to revert it. --catslash (talk) 23:38, 8 January 2018 (UTC)Reply
    I haven't seen that approach used before but I don't think it's forbidden so I've struck the comment. Mike Christie (talk - contribs - library) 12:28, 9 January 2018 (UTC)Reply
  • I think the "Stripline was the earliest form" sentence is out of place where it is in the lead, between the list of four forms and the description of the same four. How about starting the paragraph "The earliest form of planar transmission line was conceived during World War I by Robert M. Barrett. It is known as stripline, and is one of the four main types in modern use, along with microstrip, suspended stripline, and coplanar waveguide. All four of these..." or something like that?
  • Many forms have a narrower bandwidth and in general they produce more signal distortion: it's not clear to me what the comparison is to -- narrower than what? More signal distortion than what? I think this must refer to those forms that can't support the same mode as a pair of wires, but it should be clear. The same is true of the last sentence of that paragraph, I think.
  • Planar transmission lines can be used for much more than interconnecting components. They can also be used to construct components. Suggest "Planar transmission lines can be used for constructing components as well as interconnecting them" as more concise.
  • Lumped passive components are often impractical at microwave frequencies for this reason, or because the values required are impractically small to manufacture: I don't understand the "or" here; what's the difference between the two points? Isn't it just "...often impractical at microwave frequencies, because the values required..."?
    • No, the first point concerns the physical size of components compared to size of waves. The second point concerns the electrical value of a component. For instance, making a capacitor with a capacitance less than a picofarad is a design nightmare. The conductors connecting to it are going to have a stray capacitance way more than the component you are trying to connect in the circuit. SpinningSpark 01:07, 9 January 2018 (UTC)Reply
      Are the two things connected? That is, if you were trying to build a component with a tiny capacitance, would you be doing so in order to make it small enough to fit into a lumped component? Also, why are lumped passive components specifically called out here? There's no mention of passive components in the body of the article, at least not using the word "passive". Mike Christie (talk - contribs - library) 12:28, 9 January 2018 (UTC)Reply
      • The two things are indirectly connected in that smaller values generally lead to smaller physical sizes. However, the small value is not chosen in order to produce a small size. Rather, it is a consequence of smaller values are required at higher frequencies to produce the same impedance. This is true of capacitors and inductors, but not resistors. Passive components are explicitly mentioned because it is precisely those components that can be replaced by transmission line circuits. Perhaps this should be explained in the body of the article, but this was the kind of ground I had intended to cover in the redlinked distributed element circuit article (unless someone else like Catslash gets there first due to my current Wikipedia laziness) SpinningSpark 14:36, 9 January 2018 (UTC)Reply
        I see the distinction, and I understand why the physical size prevents the components from being lumpable, if that's a word. For the point about electrical values, I'm not seeing why that's relevant in this sentence. Skipping the "for this reason" point we're saying "Lumped passive components may be impractical at microwave frequencies because the values required are impractically small to manufacture". I can see that a picofarad capacitor can't be built because of the stray capacitance issue, but why does that specifically affect the ability to treat passive components as lumped? Why isn't it a more general problem affecting circuits at these frequencies? Mike Christie (talk - contribs - library) 23:28, 11 January 2018 (UTC)Reply
        • For the point about electrical values, I'm not seeing why that's relevant... It's relevant because the inability to (easily) manufacture a lumped component forces the choice of DE circuits.
        • ...why does that specifically affect the ability to treat passive components as lumped? It doesn't, although failure to lump may also be a problem at the same time. The point is that it forces the designer to move to DE circuitry.
        • Why isn't it a more general problem affecting circuits at these frequencies? It is. SpinningSpark 16:26, 12 January 2018 (UTC)Reply
          I've struck this point, because now I understand there's nothing wrong with the sentence. I think it might help to add "component" before "values", and I'd like to find a way to recast the sentence so it's clearer the second problem doesn't only apply to passive components, but that's not necessary for GA. Mike Christie (talk - contribs - library) 13:36, 13 January 2018 (UTC)Reply
  • Whole circuits can be built this way, called distributed element circuits, particularly distributed element filters: The "particularly" threw me for a moment. I think "Whole circuits can be built this way, called distributed element circuits; the method is often used for distributed element filters" would be clearer, assuming that's the intended meaning. Could we just say "...often used for filters", since "distributed element" as a modifier is clearly implied here, retaining the link to distributed element filter from "filters"?
  • This gives the planar technologies a big economic advantage over other forms: what other forms are being referred to? If I've understood the lead, we haven't mentioned any non-planar technologies to this point; could a "such as" be added here?
    Added ", such as coaxial cable". (I have seen antenna feed networks being manufactured in coax. A machine cut a set of lengths that were then hand soldered together. It was slow, laborious, error-prone and expensive) --catslash (talk) 00:00, 9 January 2018 (UTC)Reply

I'm going to pause here for your replies just to make sure I'm not misunderstanding things too much to be useful. Mike Christie (talk - contribs - library) 22:26, 8 January 2018 (UTC)Reply

Struck some points and left a couple of notes above. I should have time to return to this tonight. Mike Christie (talk - contribs - library) 12:28, 9 January 2018 (UTC)Reply

Continuing the review:

  • The exact mode is identified by a pair of indices counting the number of wavelengths or half-wavelengths along specified transverse dimensions (for instance TE10): I don't really follow this. I understand the idea of counting the number of wavelengths to give an index, but the example only has one number, instead of a pair of indices, and without an example waveguide geometry I don't know how to interpret it. Would a diagram be possible, showing a particular example?
    • Mode numbers rarely (if ever) go beyond a single digit. The convention in virtually every book I have ever seen is to omit the separating comma. TE10 should properly be written TE1,0 but it never is.
      Could we say, parenthetically or in a footnote, that the two indices are not separated by a comma? Mike Christie (talk - contribs - library) 13:36, 13 January 2018 (UTC)Reply
    • The linked TEM mode article is actually a redirect to Transverse mode and covers more than TEM. It has some example diagrams which might help the reader but unfortunately none of them are for planar forms so are not appropriate here. I created those diagrams more or less freehand. Planar field patterns are more complex and would really need proper plotting tools to get right. Besides, the issue of transmission modes is a big can of worms and I feel we have already gone too deeply into it for an overview article. It's very hard to generalise the importance of modes without reducing it to a trite one sentence that explains nothing. SpinningSpark 17:02, 12 January 2018 (UTC)Reply
      OK; if it were easy to do a diagram it would have been helpful, but that's fine. Mike Christie (talk - contribs - library) 13:36, 13 January 2018 (UTC)Reply
  • For waveguide resonators a third index is introduced to the mode for wavelengths in the longitudinal direction: I don't follow this at all. I can see that we'd need a third index if we want to identify what's happening longitudinally, but why does that not apply to waveguides that are not resonators? And is it possible to link waveguide resonator to something explanatory? I have enough physics to get an idea of what could be meant here, but this is the first mention of resonance in the article, and it's neither linked nor explained.
    • I've wikilinked cavity resonator which is about the most relevant article we have for that passage. We also have resonator available if a you feel a more general article would be helpful.
    • why does that not apply to waveguides that are not resonators? A signal sent down a properly terminated line will never come back. The length of line is irrelevant; it is always the same result—nothing returns. For a resonator, the line is blocked causing the wave to be reflected back and it is this reflection that sets up the resonance. The length determines the resonant frequency. It's analogous to playing a note by blowing over the top of a bottle. SpinningSpark 18:13, 12 January 2018 (UTC)Reply
      OK; I think the misunderstanding here is just my ignorance of the topic, so I've struck it. The link is helpful. Mike Christie (talk - contribs - library) 13:36, 13 January 2018 (UTC)Reply
  • The explanation of cutoff frequency seems backwards to me. I think it would be more natural for an uninformed reader to start by saying that multi-mode propagation is possible, but undesirable; then say that each mode has a cutoff frequency, then define dominant mode.
    • I don't agree. Cutoff frequency is an important phenomenon in its own right. It's the essential reason why waveguides are not used at low frequencies. It just so happens that it is also a handy way of suppressing multi-mode mode transmissions.
    • The point that multi-modes are possible should have already been clear before this point in the article. I've added that explicitly to the opening passage of the section. I've also noted that some devices actually make use of more than one mode. SpinningSpark 18:13, 12 January 2018 (UTC)Reply
      That addressed what I was looking for. Mike Christie (talk - contribs - library) 13:36, 13 January 2018 (UTC)Reply
  • designing the enclosure to be too small to support frequencies as low as the operational frequencies of the circuit: is this the same as saying "...frequencies above the cutoff of the dominant mode"? If so I think it would help to find a way to say "dominant mode" here, in order to help the reader connect the concept from the previous paragraph with this.
    • is this the same as saying "...frequencies above the cutoff of the dominant mode"? No, the dominant mode here is TEM which goes all the way down to zero (DC) so all frequencies are above the cutoff frequency of the dominant mode. The cutoff frequency of the spurious modes has ended up greater than the operational frequency, but it has been done by making the enclosure small. So surely directly saying it is achieved by reducing the size of the enclosure is clearer to the reader. SpinningSpark 19:08, 12 January 2018 (UTC)Reply
  • I'm not sure why we mention circular TE and TM modes in coaxial cables at the end of that paragraph, unless it's just an illustrative aside, which is OK. If so, perhaps we could also add whether those modes can be suppressed in coaxial cables?
    • Illustrative aside. I thought the analogy to coax would be helpful because it is easy to imagine the outer conductor of a round cable acting as a circular waveguide. It is not quite so self-evident with planar formats. I've added a note on suppression in coax (at the risk of going too far aside here). SpinningSpark 19:08, 12 January 2018 (UTC)Reply
  • Alternatively, TSE{x} etc. can be written as TE{x} etc. to achieve the same result: we haven't used "TSE{x}" up to this point, so I'm not clear what is being explained here.
  • A general question: why is the description of the formats themselves left so late in the article? As I read I keep wanting to skip forward to find out what is meant by finline or microstrip. I do see that whichever you cover first will lead to questions about the later material, since the discussion of the formats makes reference to concepts currently explained earlier in the article.
    • Honestly, this is the section of this article I have really struggled with. It is much longer than I would like it to be, and you are right, ideally it should be later in the article. It is where it is because the formats all talk about the modes they support so defining mode first makes sense. Possibly, a solution is to move it down and wikilink on first use. Against that, there is the question of whether to wikilink in-article to modes that already have articles. Also, "General properties", "Modes", "Other important parameters" form a logical progression and work together. Even "Substrates" is part of a trans-format description. How does moving the "formats" section to just below "general properties" work for you? SpinningSpark 19:48, 12 January 2018 (UTC)Reply
      After thinking about it I don't think a change is needed. It's a bootstrapping problem; you have to start somewhere, and this organization does work. Mike Christie (talk - contribs - library) 13:39, 13 January 2018 (UTC)Reply
  • Is there a possible link for "loss tangent", perhaps to dielectric loss?
  • Should "plated through holes" be hyphenated: "plated through-holes"? I see the hyphenation in the target article and it would make it easier to parse for a reader unfamiliar with the term.
    • Don't ask me, I'm no good with things like that. Logically, it makes sense as it is a through hole that has been plated. However, a more common hyphenation (including in the Wikipedia article) is "plated-through hole". Arguably, a hole that has been plated through is also correct. "Plated-through-hole" is also pretty common, as is no hyphenation at all. SpinningSpark 20:57, 12 January 2018 (UTC)Reply
      Striking since it's not an issue for GA. "Plated through-holes" makes the most sense to me, but since there's variation in the literature I won't try to impose a preference. Mike Christie (talk - contribs - library) 13:36, 13 January 2018 (UTC)Reply
  • FYI, the {{delta}} template, with no parameters, gives a much nicer-looking delta than the default font: δ instead of δ.
    • done.
  • Why is the section heading "Suspended stripline" but the related main article "air stripline"? You say "suspended stripline is a type of air stripline"; so there are other types of air stripline?
    • Yes, as the air stripline article explains, there is more than one form. This article concentrates on the printable forms, the overwhelming form used in manufacturing today. Any one of the sections could be expanded with more obscure or historic forms, but the overview article should concentrate on the main forms and let the subsidiary articles deal with some of the less common. SpinningSpark 21:30, 12 January 2018 (UTC)Reply
  • The idea of two conductor stripline is to compensate for air gaps between the two substrates: The diagram for stripline makes it seem that the strip conductor is embedded in one of the ground planes so that it is flush with the surface. From that, the description of two conductor stripline made me think it would be stripline in which both ground planes had a strip conductor, flush with the surface. The picture of two conductor stripline shows the conductor is not flush in either ground plane, though. What am I missing?
    • I don't think you can be reading the diagrams right. First of all, the strip is not embedded in the ground plane, it is embedded in the dielectric. See the colour key on the first diagram. Secondly, the usual method of embedding the strip is to make two separate boards with the srip on just one of them, then sandwich them together. The strip is not flush with the surface of either board, but is slightly proud of the one it is printed on, and when fully assembled, proud of the blank one as well. Two conductor stripline has a strip printed on both boards, again both proud of their respective dielectric. SpinningSpark 21:58, 12 January 2018 (UTC)Reply
  • The bilateral structure can also be used to couple two independent lines across their broad side. This gives much stronger coupling than side-by-side coupling: I don't understand what's meant by "coupling" here. Is there a linkable article?
  • There's no discussion of B and D in the "Coplanar variants" section.
  • Any reason why there's no diagram for SIW ridge waveguide? You have a diagram for everything else.
    • Partly, it was diagram exhaustion by the time I got to it. An article can become overloaded with diagrams and we can't possibly document the entire zoo of variants in an overview article. Partly, its because the source cited did not provide a diagram to refer to. This would be a subject to expand on if the ridge waveguide article ever gets written. SpinningSpark 00:14, 13 January 2018 (UTC)Reply
  • Just checking: is "Jameison" a typo? It's usually "Jamieson".
  • As far as I can see the abbreviation "MIC" used in the history section is not introduced above; similarly for MMIC.
  • I don't know if the sources have anything to say on this, but it's interesting that imageline was introduced in 1952 but is still "largely experimental".
    • Seems to be one of those things that academics love to play with and write papers on, but it has not caught on with the manufacturers as it doesn't yet work very well in practice. This could well change with the current rapid rise in optical electronics. Its still a developing field and hard to say what direction it will take. But given the heavy investment in planar forms of manufacturing that already exist, some kind of planar format is likely to prove popular through familiarity if nothing else. I might also mention that coaxial cable was invented by Heaviside in 1880 but didn't see any real use until the 1930s. Sometimes it takes a long time for these things to be taken up. SpinningSpark 00:43, 13 January 2018 (UTC)Reply
  • related by a reciprocal function: might be simpler to say "inversely related".

That's everything I can see. Mike Christie (talk - contribs - library) 11:58, 12 January 2018 (UTC)Reply

convenience heading

edit

I'm going to go ahead and pass this for GA; there are a couple of remaining minor points, but they're not issues for GA.

  • I think a footnote explaining that the indices are not comma-separated would be helpful.
  • The two-conductor stripline diagrams and the text still seem to me slightly out of sync. (Yes, I forgot the key; I meant dielectric in my comment above.) Your explanation in the notes on this page makes everything clear, but the diagrams are slightly inconsistent with each other and the text doesn't clarify the point I was asking about. In the stripline A diagram the metal line appears to be flush, but at any rate there is certainly no air space between the upper and lower dielectric. In D there's an air gap that is not that different in size from the ones shown in B and C, but the description makes it sound as if the whole point of D is to eliminate air gaps. Based on your comments above I think I now understand what's really going on, but the text and images aren't working together at this point.
  • I've redone the diagram to more realistically show the gaps on the D diagram. The diagram is not accurately to scale, it is just a diagram. The strips in reality are much thinner, more like kitchen foil, but have been enlarged to make the structure clear. SpinningSpark 15:17, 13 January 2018 (UTC)Reply
    The revised diagram makes it much clearer; I think that's a big improvement. Mike Christie (talk - contribs - library) 18:28, 13 January 2018 (UTC)Reply

Other than that I think everything is fine; in some cases I misunderstood the article, from a lack of expertise. I hope my ignorance hasn't made this review too painful; thanks for an educational experience. Mike Christie (talk - contribs - library) 13:47, 13 January 2018 (UTC)Reply

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