Talk:Waveguide filter

Filter-like devices
[Please excuse my starting the talk page with unconstructive criticism (in user-space too).] The Filter-like devices section is somewhat off-topic. Diplexers and multiplexers involve filtering and so certainly should be described. The proposition that any device which employs steps (rather than tapers) is functionally a filter is an idea with some merit, but it is not usual to refer to such devices as filters and therefore WP may be the wrong place to air such an idea. In any case, the Moreno cross-guide coupler does not fall into this category, since it is not reliant on the phase-difference of the signals coupled through the two holes (though this helps). A one-hole cross-guide coupler will function perfectly well as it primarily depends on the relative phase of the two polarizations across the hole (parallel to the guide axis and parallel to the broad wall), or equivalently on whether the field in the hole is LHC or RHC polarized (which does not depend on the wavelength). --catslash (talk) 17:09, 21 April 2013 (UTC)


 * Thanks for noticing, I'm surprised your still watching after all these years, but now I'm retired I'm determined to finish it soon. As far as the steps=filters issue goes, one of my main sources is Matthaei et al who devotes a large portion of the book to the concept that impedance matching (stepped or otherwise) does equal filter design.  You have a point about the Moreno coupler (although I have not claimed that it is a filter in the article).  A multi-hole Bethe-hole coupler or similar would be better, but I can't find a free photo of one - except tangled in with a mess of other "plumbing".  Spinning  Spark  17:55, 21 April 2013 (UTC)


 * Watching dormant pages costs zero effort. Seeing the hours your were devoting to this work, I did suspect that you were free from paid employment.


 * The idea that multiple discontinuities (steps is too specific) necessarily constitute a filter is becoming more appealing to me. However attaching an over-generalized concept to a term ultimately renders it meaningless (see the Signal (electrical engineering) article for an example of an unhelpfully broad definition). That a smoothly tapered transition might constitute a filter seems indefensible. Perhaps it would be possible to say that devices such as (some) couplers and (some) transformers share the multi-section structure of filters and are regarded by authors such as Matthaei as being filters - that is, naming the author in the text in order to avoid giving undue weight. Should you disagree however, I shall not pursue this issue further.


 * When the critical structures of a device are internal (as with the Bethe-hole coupler), it's probably best to stick with diagrammatic representations, and use photographs when the structure can be seen from the outside (as with the transformer on the OMT, or with the post filter). --catslash (talk) 23:51, 22 April 2013 (UTC)


 * I don't really see the need to explicitly say the filter view of stepped impedances is due to Matthaei (actually, it is due to Leo Young - see this paper). Matthaei is very highly regarded and many other authors follow the same thinking.  For instance Das and Das talk about designing stepped impedance matching with a maximally-flat (ie Butterworth) or Chebyshev response.  Quite patently filter-like designs.  Not sure why you raised smoothly tapered transitions, that's not in the article at all so isn't really an issue.  But to take up your point, a smooth taper can be viewed as stepped impedances with an infinite number of steps, or equivalently, stepped impedances can be viewed as an approximation to a smooth taper.  Again Das & Das is an example source.  This is entirely analogous to a low pass filter divided into more and more smaller inductors and capacitors eventually taking on the nature of a smooth transmission line and is exactly how filters were invented in the first place!


 * On the Bethe-hole coupler, I already have a diagram which I did for the power dividers and directional couplers article, but I have an aversion to repeating the same diagrams in different articles. Maybe I'll replace the Moreno coupler later if nothing else turns up, but another issue is that I don't want the article to be all diagrams.  Real photos are beneficial to readers not familiar with the technology. Feel free to do something yourself if you like.  Spinning  Spark  08:46, 23 April 2013 (UTC)

Citation variation
Why were all my attempts at rather basic standardization of the references reverted and labelled "gratuitous"? It doesn't seem very relevant to evoke WP:CITEVAR either, since this doesn't adhere to any standard whatsoever. It's not like we're talking about a swtich from Harvard to parenthetical here or anything.

Peter Isotalo 11:52, 5 May 2013 (UTC)


 * doesn't adhere to any standard whatsoever, isn't that the whole point? No citation style is preferred over any other. I don't see how you can think that "[e]ditors should not attempt to change an article's established citation style merely on the grounds of personal preference, to make it match other articles, or without first seeking consensus for the change" is not relevant here.  I am aiming this article at FA and that will inevitably mean a number of reworkings along the way and additional sources and citations.  Are you proposing to take part in this work? Or add substantively to the article?  If not, you change of citation formatting is only having the effect of forcing me to use it in the future, or else risk FA rejection for inconsistent style.  I find it a little irritating being forced to either accept a mode of working I don't like or else get into reverting people.  We can talk about my specific reasons for using particular styles if you like, but unless their is a special relevance to this article I would prefer that happened on a user talk page, or the talk page of a relevant guideline.  Spinning  Spark  13:21, 5 May 2013 (UTC)

Tuning screw insertion
Is this correct: ''However, when the screw has been inserted a distance λ/4 it resonates equivalent to a series LC circuit. Inserting it further it causes the impedance to change from capacitive to inductive, that is, the arithmetic sign changes.''? Surely λ/4 means touching the other side and therefore certainly inductive? --catslash (talk) 00:15, 22 December 2013 (UTC)
 * It's λ/4 of the free space wavelength, not the guide wavelength. The source is here.  Spinning  Spark  01:46, 22 December 2013 (UTC)
 * Of course: only at cutoff is λ/4 is the guide height - at higher frequencies it is somewhat less. Please excuse my stupidity. --catslash (talk) 02:50, 22 December 2013 (UTC)

Circular definition
Could the lede be made to sound less like a circular definition?I had to laugh when I saw this was the start of a featured article: "A waveguide filter is an electronic filter that is constructed in waveguide technology." Sounds too much like "A mush wump is a wump made from  mush." Perhaps spell out "waveguide technology" briefly in the first sentence by combining it with the brief explanation in the second sentence. Edison (talk) 15:53, 10 January 2014 (UTC)
 * It's saying that it's an electronic filter (in a particular medium). --catslash (talk) 23:26, 10 January 2014 (UTC)
 * cf. A waveguide filter is a filter for removing waveguides from soup --catslash (talk) 23:36, 10 January 2014 (UTC)


 * The beginning of the lede should define the topic of the article per MOS:BEGIN. Does User:Edison have a suggestion for a better definition?  Spinning  Spark  00:34, 11 January 2014 (UTC)


 * In the context of the first paragraph, I think the first sentence is fine. It defines the topic in terms of filter and waveguide. Then in the second and third sentences, waveguide and filter are explained. If the reader is willing to read the whole paragraph, they will be able to understand the topic in terms of simpler concepts. The main gap in the explanation that I see is that a reader would need to realize that electromagnetic wave and signal represent the same thing here. --Mark viking (talk) 01:25, 11 January 2014 (UTC)


 * How does this sound?


 * A waveguide filter is a type of waveguide comprised of hollow metal tubes used to electronically filter electromagnetic waves transmitted though it, allowing certain frequencies to pass through (the passband), while others are rejected (the stopband). Ward20 (talk) 03:48, 11 January 2014 (UTC)


 * Not very good. How much of the article are you proposing to replace?  As a replaement for just the first sentence it is repetitive of subsequent sentences.  Waveguide filters are not a type of waveguide, unless automobiles are a type of sheet metal.  You have conflated the description of "waveguide" with "waveguide filter".  The description of waveguide was deliberately given its own sentence for the benefit of the general reader.  Contiguous links are not recommended by the style guidelines, one of the links is a dab page, and if it were not a dab page it now has to be piped instead of a direct link.  Not quite an Easter egg but moving that way.  Filtered electromagnetic waves are not "transmitted through" - unless the filter is not working.  You have a spelling mistake and "comprised of" is poor grammar where "comprising" would do.  Spinning  Spark  10:31, 11 January 2014 (UTC)


 * How about just "A waveguide filter is a filter for use in a waveguide system, that removes certain frequencies in the signal.", or words to that effect. MinimanDragon32 (talk) 12:05, 9 May 2014 (UTC)
 * How about just leave it as it is?


 * Why do people want to change a simple, direct, correct, and understandable statement to something that is more complicated or even wrong. There is no need to go banging on about what kind of filter function or the system that it is used in.  That doesn't matter.  It's made of waveguide; that's the only relevant thing needed to define it.  Other than that, it can be any function or applicaton.  Take a look at this dielectric resonator filter.  It has coaxial connectors so is clearly not intended for use in a "waveguide system".  Yet it's internal construction is identical to what it would have been if it had waveguide connectors.  Has it suddenly stopped being a waveguide filter because of that?  Waffle-iron filters are unarguably a type of waveguide filter yet they are commonly used to screen the output of commercial microwave ovens operating a continuous process.  That is not being used in a "waveguide system"; it is being used in a biscuit baking system.  Spinning  Spark  13:00, 9 May 2014 (UTC)

Stub filter
I haven't got a copy of Matthaei, but the filter presently shown in Fig. 12 is a bandstop with a stop-band of approximately 1.15 fcutoff to 1.35 fcutoff (it would benefit from the stubs being a bit closer together - the stub spacing (measured centre-to-centre) appears a little greater than the stub length). If the filter described is the same as that pictured, then it is likewise a band-stop. It is possible that the stubs are supposed to be in the narrow wall, but it seems unlikely (they would probably need alternate between the two sides to fit them in). Perhaps you could re-examine Matthaei? --catslash (talk) 11:44, 20 January 2015 (UTC)
 * Hi Catslash, thanks for responding. If it had been anyone else but you, I would have reverted without thinking too much about it, but as I know you know what you are talking about, I checked the sources carefully before reverting.  Still, it's always possible that I have a huge misunderstanding of what's going on.  The Matthaei source (p.726) has a waveguide bandstop filter with stubs on the broad wall of the waveguide spaced 3λg/4 apart and coupled into the main guide with small irises.  The stubs are approximately λg/2 in length.  This is stated explicitly, not just derived from the drawing dimensions, and later in the chaper (p.753) the exact lengths are calculated.  The Ke Wu source shows a similar, but undimensioned, bandstop filter which has about the same ratio of dimensions.  Now if λ/2 stubs are bandstop, then λ/4 stubs are going to be bandpass surely?  Or am I missing something basic?  Das & Das  (a different book to the source in the article) gives the impedance for a stub on the broad wall of length less than λg/4 as jZ0tan2πl/λg.  Now as l approaches λg/4 the impedance approaches infinity, suggesting a parallel LC equivalent circuit is required.  That in turn suggests a bandstop filter.  So perhaps an iris coupled filter is a completely different beast with a large capacitance from a stub slightly less than λg/2 resonating with the iris inductance.  This section clearly needs either new sources or rewriting to comply with the ones we already have.  I'm going to self-revert to your version. SpinningSpark 13:35, 20 January 2015 (UTC)
 * Yes, I have in the past seen a bandstop filter with broad-wall λg/2-long stubs 3λg/4 apart and coupled to the main line through small-aperture irises. It gave a narrow notch in the transmission (not a broad stop-band). The irises turn the stubs into resonant cavities perhaps - I need to go away and think about this. --catslash (talk) 14:47, 20 January 2015 (UTC)
 * Matthaei agrees that it is a narrowband design. And on p.275 the filter "uses band-stop resonator cavities which are coupled to the main waveguide by inductive irises." SpinningSpark 15:11, 20 January 2015 (UTC)
 * Having gone away and thought and also found a sketch of the filter I mentioned earlier, I find it is exactly as you describe: the irises are inductive at all frequencies of interest, while the stubs/cavities are 0.45λg (i.e. capacitive) at the stop-frequency. Essentially each section is a capacitive stub shunted by a lumped inductance (except that the cavities/stubs have tuning screws). --catslash (talk) 22:08, 20 January 2015 (UTC)