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Talk:Distributed-element filter

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Latest comment: 15 years ago by Spinningspark in topic Prose comments by Cryptic C62
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Rewrote the lead

Latest comment: 15 years ago1 comment1 person in discussion

The old lead had some problems.

A distributed element filter is an electronic filter designed for frequencies above the VHF band or thereabouts. At these frequencies the wavelengths of the operative signals are shorter than the size of the device being constructed and it is no longer possible to use the more familiar lumped element model. Filters and other passive circuitry are instead designed using the distributed element model in which the components of the circuit are treated as being transmission lines, which indeed, they effectively are.

Note that at the top of VHF band the wavelength in air is ~1 meter. Lumped elements crap out about here but clearly "wavelengths of the operative signals" are not "shorter than the size of the device being constructed". I've also added some helpful wikilinks. I think the new language flows a bit better as well but YMMV. JPatterson (talk) 20:34, 15 February 2010 (UTC)Reply

Things to improve

Latest comment: 15 years ago10 comments3 people in discussion
  • Front figure: "for suppressing non-TEM modes of transmission" needs a cite. Adding a note on image width would help understanding the size - not everyone knows this connector type. Image file needs a better description, preferably explaining why rubber seal (moisture ?).
I have addressed the "through holes for TEM mode" issue. Image size is a bit problematic; it is not my image so I cannot retake it with a rule included. It would, of course, be possible to estimate the size from some of the circuit structures, but that is almost the definition of OR. I am against explaining the rubber seal (it is to give the enclosure an IP rating because the product is intended for outdoor use) - this is going way off-topic; there are any number of features that could be explained here. The only one mentioned, the through holes, are only described because they can easily be mistaken for a filter structure. SpinningSpark 20:48, 8 April 2010 (UTC)Reply
Regarding the via fences: there will be an internal metal lid cast with a pattern of walls on the underside, which corresponds to the pattern of via-fences. This lid is clamped down tightly onto the circuit by a large number of bolts - notice all the screw holes associated with the via fences (it can't have been screwed down very well in this example as the walls have not made a visible indentation in the metallization). The via fences connect the base of the walls to the ground-plane, so forming a number of near perfectly isolated enclosures, communicating only where the microstrip passes through a notch in the cast walls. This internal lid is in addition to a simple external lid which makes a seal with the rubber gasket.--catslash (talk) 10:41, 29 April 2010 (UTC)Reply
Regarding the photo: I've just put a more close-up view of a (just) a filter at File:Microstrip-bandpass-filter.jpg. I was going to use this to illustrate edge-coupling on the microstrip page, but never got around to writing about it. I haven't put the picture on this page, as you may feel that the existing one is better - take a look and see what you think. --catslash (talk) 16:35, 29 April 2010 (UTC)Reply
Nice picture. That would be great for the parallel-coupled lines section. I don't think we should expand on via fences in this article, it is only mentioned for clarification purposes. I have red-linked it with the intention that an article should go there someday. SpinningSpark 07:35, 30 April 2010 (UTC)Reply
OK. I just felt that the phrase for suppressing non-TEM modes of transmission though strictly speaking true, is rather misleading. --catslash (talk) 11:55, 30 April 2010 (UTC)Reply
  • There is some imbalance between figure captions - one cites references and others don't. I probably understand why, but this could be picked up at FAC.
There is usually no need to give citations to image captions unless they introduce facts not in the main text. All the figures here are described in the text where a citation is given. I have made an exception for figure 2 because it is a composite from a number of different sources and I wished to make it clear which filter structure came from which source. SpinningSpark 20:30, 9 April 2010 (UTC)Reply
  • Add history subsection?
I am actively looking into this. The history of the various technologies (co-ax, stripline, microstrip, waveguide etc) is well documented, mostly of them starting in radar in WWII and the filters in these technologies followed shortly after their first use. However, sources dealing with distributed element filtering as a general topic are a bit harder to find and I need to see if enough material can be gathered to write a worthwile section. SpinningSpark 20:30, 9 April 2010 (UTC)Reply
I have now started a history section. There is still a bit more that could go in, but I think the point is now addressed. SpinningSpark 18:13, 11 April 2010 (UTC)Reply
done SpinningSpark 12:21, 11 April 2010 (UTC)Reply

Prose comments by Cryptic C62

Latest comment: 15 years ago43 comments2 people in discussion
Resolved comments
  • "Its purpose is to allow a range of signal frequencies to pass, but to block others." What is a "signal frequency"? I would be satisfied with a simple wikilink, but there doesn't seem to be an article with such a title.
  • "There is no precise frequency beyond which distributed element filters must be used but they are especially associated with the microwave band (wavelength less than one metre)." The use of "beyond" seems a bit imprecise. Either "above" or "below" should be used instead. Also, why does the main sentence discuss frequency while the parenthetical uses wavelength? I'm aware of how the two are related, but this will probably be a source of confusion to those who are not already familiar with the terminology.
  • Fixed "beyond". I think the mixed use of frequency and wavelength is unavoidable in this article. There are good reasons why signals are invariably described in terms of frequencies, but circuit structures are described in terms of wavelengths. Length, in fact, is an additional element in distributed circuits, although the article has not delved into this aspect (but maybe a future one will). The way to deal with this is head-on in the lede, establishing that frequency rises as wavelength falls. Math markup could be used to give the exact relationship but I have tried to avoid that as much as possible in this article and I don't think that it is necessary for understanding. On a pedantic note, one metre is the formal boundary of microwaves. Many books will give this as 300 MHz, but the two are, of course, only approximately equal - and not equal at all in a high permittivity medium. SpinningSpark 21:58, 17 June 2010 (UTC)Reply
  • "All of the well-known filter classes used in lumped element designs (Butterworth, Chebyshev, etc.) can be implemented using a distributed element approach." I am of the opinion that the phrase "well-known" should always be avoided in an encyclopedia. In this case, the sentence implies that the lesser-known classes can't be implemented using the distributed approach, which is silly. Perhaps just "Most filter classes used in lumped element designs (such as Butterworth and Chebyshev) can be implemented using a distributed element approach." would work better.
    I think we can safely use "all filter classes" here. SpinningSpark 18:03, 18 June 2010 (UTC)Reply
  • I strongly believe that the first and third paragraphs of General comments should be contiguous, as they both discuss the actual topic whereas the second paragraph discusses the article itself. Whether the order should go 2-1-3 or 1-3-2 is up to you. Also, if the second paragraph discusses the format of the diagrams, shouldn't the accompanying image also be such a diagram?
  • 1-3-2 looks good to me. The reason the figure 2 image is in the article has nothing to do with the paragraph it is attached to, that is just a convenient place to park it. The article benefits from a photograph (as opposed to a diagram) of a DE filter. The lede image is good in that it provides a variety of filter structures, but it is busy with a lot of non-filter circuitry as well. This image shows a filter by itself. Such an image is best early in the article, but the lede position is already taken, and besides, the alternative of placing it in the parallel-coupled section is not viable because it has no room for another image. SpinningSpark 23:05, 18 June 2010 (UTC)Reply
  • "On the other hand, antenna structure dimensions" I'm thinking "antenna" would be a good thing to wikilink, but there are so many choices for articles to link to! Your call.
  • "...can be chosen by design to function, to a first approximation, like lumped inductors..." Yikes, the use of "to a first approximation" makes this sentence way more technical than it needs to be, especially since this is the only instance of "first approximation" in this entire article. How about "...can be chosen by design to function in roughly the same manner as lumped inductors..." ?
  • "The development of distributed element filters was spurred on by the wartime need of the military for radar and electronic counter measures during World War II." I suggest replacing "by the wartime need of the military" with "by the military need" or "by the military's need". The word "wartime" is very redundant given that the sentence ends with "during World War II".
  • "Development of distributed element filters was underway in the years before World War II." There is a bit of ambiguity with the phrase "the years before World War II". Some readers might interpret this as meaning the late 1930s, some (milhis buffs) might interpret it reaching all the way back to the end of World War I in 1918. Also, "was underway" is a useless phrase. Saying when something "was underway" gives no indication of when it started.
  • I don't really see the problem here. The opening sentence is a general statement that is then expanded on by the following sentences. The nature of the work is stated and the papers referenced. The probable birth is clearly identified as 1927, so no one should be thinking 1918. The real drive to develop this technology, however, was during WWII which is why the opening sentence references the war. SpinningSpark 23:23, 20 June 2010 (UTC)Reply
  • "The introduction of printed planar technologies greatly" Should "printed planar technologies" link to Printed circuit board or am I mistaken?
  • That's a difficult one to answer, I would say no - it is linked already earlier in the article where it is made clear that pcb technology can be used to make planar DE circuits. That is a better link as pcb is linked directly, linking "printed planar technologies" has the potential to confuse the reader as the pcb article only discusses these briefly. SpinningSpark 23:23, 20 June 2010 (UTC)Reply
  • "He published a set of transformations known as Kuroda's identities in 1955, but his work was written in Japanese and it took several years to reflect his ideas in the English-language literature" How about "He published a set of transformations known as Kuroda's identities in 1955, but his work was written in Japanese and it took several years for his ideas to enter the mainstream English-language literature." instead?
  • I agree except that "mainstream" should be dropped, implying as it does that one has to publish in English to be mainstream. The current wording of this sentence is due to Materialscientist - it may be worth checking his original edit summary to see if he had a particular reason for stating it that way. SpinningSpark 23:23, 20 June 2010 (UTC)Reply
  • I disagree that the use of "mainstream" implies that one must publish in English to be mainstream. What I intended to convey was that within the English-language literature, there is a mainstream which it took a while for Kuroda's work to break into. However, rather than fussing around with word order, perhaps both issue can be sidestepped with a different rewording altogether: "He published a set of transformations known as Kuroda's identities in 1955, but his work was written in Japanese and it was several years before his ideas were incorporated into the English-language literature." Better? --Cryptic C62 · Talk 15:31, 22 June 2010 (UTC)Reply
  • "There are many component forms used to construct distributed element filters, but all have the common property of causing a discontinuity on the transmission line." I'm not sure of the exact meaning of "discontinuity" in this context, which I suspect will be the case for many other readers. At first I thought it meant a physical break in the wiring, but after reading the rest of the paragraph, that doesn't seem right. Reading transmission line doesn't help either, as that article doesn't use the word "discontinuity" even once!
  • The sense continuity is being used here is in the mathematical sense of a continuous function. The transmission parameters are normally continuous functions of distance along the transmission line. A discontinuity in the transmission parameters is caused by a sudden change in line geometry (this can be a narrow physical gap, but also a step change in conductor width will do it, or attaching a component at that point). There is a step change in the transmission parameters at the point of the discontinuity. Such functions are said to be piecewise continuous. I have endeavoured to avoid introducing unnecessary mathematical concepts into this article and it would also be sidetracking the article somewhat to give lengthy explanations of DE theory, there are other articles for doing that. Suggestions how this could be clarified while keeping the focus on filters are welcome. SpinningSpark 18:03, 18 June 2010 (UTC)Reply
  • I don't fully understand the material that's being linked to, but if you're confident that it's the best way to explain a discontinuity, then I'm all for it. I've gone ahead and added the link. --Cryptic C62 · Talk 15:31, 22 June 2010 (UTC)Reply
  • "Early stripline directly coupled resonator filters were end-coupled," Very awkward wording. I expected "stripline" to be the subject of the sentence and started hunting for the verb after "directly" and got very confused. Is "stripline" being used as an adjective here? Should "directly coupled" be interpreted as a single adjective ("directly-coupled")? --Cryptic C62 · Talk 15:31, 22 June 2010 (UTC)Reply
  • "by telecommunications companies to provide the "backbone" of their networks." Direct quotations should be followed by a citation. Did this come from Huurdeman or from some other source?
  • Perhaps I should have used italics instead of quotes. Or possibly wikilink backbone although sadly, the author of that article has written exclusively about computer networks even though the usage of backbone in telecommunications is much more general than just IT. SpinningSpark 21:25, 22 June 2010 (UTC)Reply
  • "...inductance and capacitance (and resistance, but that rarely features in filter designs) are distributed along the length of conductors, and the two..." It seems contradictory to have a parenthetical comment (intended to give "extra" details) in the lead (intended to give a broad overview of the topic). Unless you can think of a way to work it into the sentence without adding a huge amount of clunky commas, I suggest dropping the parenthetical altogether. Also, this seems somewhat contradictory with the opening sentence. Perhaps the opening sentence could be reworded to "in which capacitance, inductance and sometimes resistance" to avoid implying that all three are equally important.
  • Decline to do this. All three are equally important and resistance absolutely has to be mentioned. The filter designer does not want it: it is parasitic to his design as they say in the terminology, but he is going to get it anyway. It does not feature in the design in the sense that the designer has deliberately introduced capacitance and inductance, but resistance has crept aboard uninvited like a ship's rat. I might also mention that there are some rare filter designs that do deliberately incorporate resistance, see this patent by Hendrik Bode for instance. The lede should be readable by anybody, as reviewers never cease to remind me, and we should not assume prior technical knowledge. Equally, we should not assume that the reader does not know what the basic three passive elements are and feel we are free to leave one out thinking it will not be missed. In fact, a reader who has come to this article probably will know this, and almost everybody has at least heard of resistance and knows that it is an element of electrical circuits. To not mention resistance will leave the reader asking what has happened to it. I will, of course, welcome rewording to make it less clunky. SpinningSpark 21:58, 17 June 2010 (UTC)Reply
  • Very well explained. The question now is how to make it less clunky. I think the phrase "but that rarely features in filter designs" does not adequately explain what you've just told me, nor would it even be possible to concisely explain the matter without cluttering up the lead. Why not just "...inductance, capacitance and resistance are distributed..."? --Cryptic C62 · Talk 01:51, 18 June 2010 (UTC)Reply
  • Because the lede has already opened with "capacitance, resistance, inductance". It then goes on to say LE filters usually consist of capacitors and inductors. The secondary point is that resistance is not usually "designed in" with filter circuits. To not say this leaves the reader wondering where it has gone in this story. SpinningSpark 18:03, 18 June 2010 (UTC)Reply
  • Two options that have not been explored: First is to use a footnote, which would allow you to explain the matter in more sufficient detail without clogging the lead. The second would be to simply add another sentence after the end of this one. The sentence that currently follows it, ("There is no precise frequency above...") doesn't seem closely related to this sentence, so the flow of the paragraph wouldn't be lost. --Cryptic C62 · Talk 19:51, 18 June 2010 (UTC)Reply
  • "The increasing miniaturisation of electronics means that circuits which were once large compared to λ no longer are." This (quite wrongly) implies that an individual circuit will physically shrink over time. Perhaps "The increasing miniaturisation of electronics means that, unlike their older counterparts, modern circuit elements are generally not large compared to λ." ?
  • I sincerely doubt that anyone will put that reading into the sentence, but I have no objection to a rewording in principle. Your suggestion, however, is confusing components/elements/circuits and it is also incorrect that "modern circuits are generally not large compared to λ." There is a trend, but there is still a point (implementation technology dependant) beyond which DE is still required. SpinningSpark 23:05, 18 June 2010 (UTC)Reply
  • My suggestion was merely an attempt to make it clearer that it is not the individual circuits themselves that are shrinking, but instead the designs for the circuits. Since I'm quite evidently not an expert on the subject, do you have any ideas for how to make this distinction clearer? Also, it would be nice to rid the sentence of the awkward ending "no longer are." --Cryptic C62 · Talk 15:31, 22 June 2010 (UTC)Reply
  • Reworded to get rid of the ugliness. The idea that this could be misread as circuits physically shrinking is pedantic nonsense. "The increasing streamlining of automobiles" would be understood by no one as meaning the "sit up and beg" radiator grille of ones Rolls-Royce Silver Shadow has slowly been worn away by air resistance over the years. SpinningSpark 12:24, 26 June 2010 (UTC)Reply
  • "Such applications are part of large capital investment programs. However, mass-production..." The use of "however" should set up a contrast between two ideas or two time periods. I fail to see such a contrast between these sentences.
  • The contrast was supposed to be between the initial applications where cost was not the overriding issue (the major costs of setting up a telecommunications network are getting all that kit to the top of obscure hills in inaccessible places and building towers to house it all. A piddling little electronics gadget does not really enter the economics, even if it is not made in the most cost effective way) and equipment for the consumer market where shaving fractions of a penny from unit costs can be significant for profitability because of the high volumes. SpinningSpark 21:25, 22 June 2010 (UTC)Reply
  • "(often quarter wavelength)" I'm thinking that this can be replaced with "(0.25λ)" to make it consistent with the General comments section.
  • it can be, although some reviewers might prefer it in words. I would write it as "(often λ/4)"; stating as a fraction is more normal for mutiples of λ/4 and make the function clearer; "often" is still needed because other lengths can have a useful function as well. SpinningSpark 18:45, 24 June 2010 (UTC)Reply
  • "These multiple element filters can implement any of the filter families..." I'm confused. The lead explicitly states that all filter classes can be implemented using a distributed element approach. This is the only instance of "multiple element filters" in the entire article, leading me to believe that "these multiple element filters" refers to the "hybrid mixture" in the previous sentence.
  • You are confused because element is not being used with the same meaning here. This is bad, let me think of a better way of writing this. I guess component will have to be used but I don't entirely like that because stripline circuits are made as a single piece, not from components joined together. SpinningSpark 18:45, 24 June 2010 (UTC)Reply

Unresolved comments

Here are some comments on the article's prose intended to help make the article accessible and precise:

  • "The generic term stripline in modern usage usually refers to the form then known as triplate" Let me just check to see if I'm reading this correctly: Barrett invented something which he called "stripline". That particular technology received competition from another technology called "triplate". Today, the term "stripline" no longer refers to Barrett's technology but to triplate instead. Correct?
  • Not quite as clear cut as that. Stripline has become a generic term in the same way as hoover refers to vacuum cleaners and xerox machine means a photocopier regardless of who the manufacturer really is. Most of the time triplate would be meant in modern usage but it still could be applied to Barrett's original form, or some other variant. SpinningSpark 23:23, 20 June 2010 (UTC)Reply
  • I see. Such subtleties are often difficult to accurately convey in an article. How about Replacing the aforementioned sentence with the more general "In modern literature, stripline has become a generic term to describe several variations of the technology"?
  • While that is true, I would still like to say that stripline unqualified most often means the triplate form. Some authors use stripline and triplate interchangeably, some will use a qualifying adjective where distinction is necessary, such as air stripline, triplate stripline or dual stripline for instance. SpinningSpark 21:25, 22 June 2010 (UTC)Reply
  • If triplate is the more common meaning of the modern term stripline, does that mean that triplate has become the more popular format? If so, how about "Though triplate has since become the more popular format, stripline is often used as a genericized trademark." or something like that? --Cryptic C62 · Talk 01:17, 28 June 2010 (UTC)Reply
  • That would not really be accurate. If anything, microstrip is now the most popular format, and although a planar strip, the term stripline is rarely, if ever, applied to it. It is more usual that stripline and microstrip are counterposed, both terms being used generically. Unless you have a source that states x, y, or z is the most popular format I would be very uncomfortable making any such statement. It might be true that triplate is the most popular form where the medium above and below the strip are identical (this is what distinguishes it from microstrip which is air dielectric above the strip) and I can verify that was true in the time-period I was involved in design in low-power applications. But it may not be now, and high-power applications usually require an air-dielectric format. I appreciate you would like to say something more definite, but as I say, I would not want to make any sweeping statements about popularity without references. SpinningSpark 17:02, 1 July 2010 (UTC)Reply
  • "The simplest structure that can be implemented is a step in the characteristic impedance of the line" Suggest adding "in a distributed element filter" after "implemented", unless you meant that an impedance step is literally the single simplest structure ever in the history of the universe.
  • Actually, now that I think about it, there is an ambiguity here that may need correction: does this sentence mean the specific "the simplest structure that can be implemented in a distributed element filter" or the more general "simplest structure that can be implemented in the distributed element model"? --Cryptic C62 · Talk 01:17, 28 June 2010 (UTC)Reply
  • "behave as shunt LC (anti-)resonators" Very awkward construction, and the meaning isn't entirely clear. Suggest replacing with "behave as shunt LC resonators or antiresonators", assuming that that is the correct interpretation.
  • "they have the drawback that it is impossible to create an ideal open circuit" Because I'm a physics nerd, I automatically assume that "ideal" has some special meaning, as is the case for ideal gas. What meaning is it intended to convey here?
  • "and consist of a coil of wire, on a former and core" What is a "former"? The article former is of no help.
  • The following two sentences seem to contradict each other: "While open-circuit stubs are easier to manufacture in planar technologies, they have the drawback that it is impossible to create an ideal open circuit (see figure 4(b)), often leading to a preference for short-circuit stubs (one can always be used in place of the other by adding or subtracting λ/4 to or from the length)" and "Coupled lines tend to be preferred in planar technologies, where they are easy to implement, whereas stubs tend to be preferred elsewhere." If open-circuit stubs are easy to manufacture in planar technologies, then how can it be that coupled lines are preferred in planar technologies because they are easy to implement?

More to come. As you make changes in the article, please respond below individual concerns so I know which are done and which need further discussion. Thanks! --Cryptic C62 · Talk 00:52, 15 June 2010 (UTC)Reply

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