Talk:Yagi–Uda antenna

Traps

A trap is not just a coil, it is a combination of a coil and a capacitor in parallel. The values for the capacitor and coil are chosen such that the trap is resonant in the middle of the band for which it is designed.

For example, if you were to design a triband yagi for 14, 21 and 28 Mhz, you would have the 2 28 MHz traps located closest to the boom, then the 2 21 MHz traps, followed by the final length of element beyond the trap.

The resonant circuit of the trap isolates the outer portions of the element from the inner portion. If you were to look at the representation for an yagi antenna element, you would see that it has 2 traps on each side of the boom. The trap's function is to isolate the outer portion from the inner portion of the element. For example, if you were to use this antenna on 21 MHz (i.e. the 15 meter band), only the portion of the antenna between the '21MHz' traps is active.

"------21MHz-----28MHz-----X-----28MHz-----21MHz------"

X = Boom

A dip meter is typically used to determine the resonant frequency of a trap.

Source: The ARRL Handbook for Radio Amateurs (1991). Antenna Fundamentals p. 17-14. Newington CT: American Radio Relay League.

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Energy Flow Diagram

Nice article! Possibly a bit too deep too quickly. Remember, we are not all wireless communications experts ;-)

Can you please provide a key for the energy flow diagram on this page? What is electric field, what is magnetic filed, what is physical antenna etc...

Perhaps we could also provide a link from here back to Tesla's experiments with wireless transmission of electrical energy.

darkside2010 00:26, 2 January 2006 (UTC)

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As you say, not everyone is a wireless communication expert, but one would be even less of one if one believed much of what is written here. I've no idea what that is supposed to be showing. Since you raised this point more than 3 years ago, and nobody has substantiated it, I think I'll remove it. Drkirkby (talk) 09:21, 18 October 2009 (UTC)

Element Spacing & Design

The statement about spacing between elements being "approximately 1/4 of a wavelength" is wrong. While spacing varies depending on design, the normal spacing is about 1/8 of a wavelength.

A good source we should footnote is http://www.cebik.com. Mr. Cebik has written a large number of articles on antenna design, many of which cover details of Yagis in far more detail than is appropriate for an encyclopedia.

Off2Explore 19:16, 27 April 2006 (UTC)

Diagram Inaccuracies

The diagram needs to be revised. The text suggests that the reflector and director are 105% and 95% of the driven element length, yet the artist has rendered .55 lambda and .45 lambda.

This article appears to contradict itself; the text has the elements on quarter-wavelength spacing (which is plausible) but the illustration image:Antena yagiuda500.png denotes one-tenth wavelength spacing. I'm presuming these aren't both correct? --66.102.80.212 (talk) 20:22, 19 March 2009 (UTC)

I found a calculator that uses a .15 lambda spacing (noted as ARRL's recommendation) and a .20 lambda spacing, referencing DL6WU. The diagram could be enhanced by indicating the range of acceptable element spacings (.10 through .25 or ?). The article could be enhanced by explaining the effects of spacing.

theoretically all spacings will work :) however, because spacing changes the impedance at the feed point of the driven element(dipole), and in the real world we only have the choice of a few cable impedances with which to connect our antenna you will see 1/10 to 1/8 wavelength typicallyBazzaar (talk) 23:36, 2 September 2009 (UTC)

Can you provide any professional reference (not amateur site) that theoretically all spacings will work? Of course you can not, since it is simply not true. Even among radio hams I have never herd that one. Drkirkby (talk) 09:17, 18 October 2009 (UTC)

I was taught that the reflector should be about half a wavelength behind the active element and that the director(s) are typically separated from each other and the active element by about a quater of a wavelength each but that there's more scope for variation with the directors. BrianDGregory (talk) 15:14, 18 November 2010 (UTC)

The diagram that shows the same one tenth wavelength between the reflector and active element as between the active element and director must surely be regarded as totally wrong. Simply making an element a little longer will not change it from a director into a reflector, it's mainly the spacing that does that. BrianDGregory (talk) 15:14, 18 November 2010 (UTC)

"I also took a specialist course in Antennas and Radar as part of an MSc. degree in microwaves and optoelectronics" did you pass? I cant tell, but your lack of understanding indicates not. —Preceding unsigned comment added by Bazzaar (talk • contribs) 14:14, 24 March 2010 (UTC)

Wording

"If one holds out one's arms to form a dipole and has the reflector behind oneself, one would receive signals with maximum gain from in front of oneself"

...Um, no, one cannot receive signals with one's arms. Not even if one wears a tinfoil hat. Why not just say that the antenna receives signals with maximum gain from the direction of the director (or smaller element)? —Preceding unsigned comment added by 99.231.124.188 (talk) 05:58, 16 June 2008 (UTC)

Cardioid?

Why exactly is Cardioid listed as a related article? The word shows up nowhere else in the entire article. Was it used in a previous version of the article? 67.82.99.84 (talk) 02:38, 26 October 2008 (UTC)

Whoops, I forgot to sign in. CarVac (talk) 02:40, 26 October 2008 (UTC)

It's not clear to me any relevance either. It has been removed Drkirkby (talk) 09:33, 18 October 2009 (UTC)

Probably had to do with a no-longer-present comparison of the radiation pattern between a yagi and a visually-confusable Log-periodic_antenna#ZL_special --Rob* (talk) 01:04, 22 September 2013 (UTC)

Description

description of this antenna type is confused with that of the log periodic type;

"directors progressively shorter than a half wavelength to couple signals of increasingly higher frequencies onto the dipole"

no, the elements in a Yagi are progressively shorter so that the phase angle of the signal in each director is changed in such a way that only in the desired direction do they combine in phase and cancel in all other directions, this is the fundamental property of the Yagi which is missing from this article

the log periodic has progressively shorter elements to allow it to cover a greater frequency range, but it has no "the dipole" the whole array is driven

excepting the use of traps, the Yagi is a narrowband antenna(a few percent of design frequency) and the log periodic a broadband antenna(octave frequency coverage)Bazzaar (talk) 23:27, 2 September 2009 (UTC)

Article is far too amateurish

Clearly most if not all of this article was written by amateur radio operator (a ham). I have nothing against them (I am one myself). But I know that a lot of this is very poor by the standards of Wikipedia. It is clearly within the scope of amateur radio, but I do not believe that the article should be written with only radio hams in mind. Specific issues I see:

• Terms like good match are not appropriate.
• I'm not sure what that energy flow diagram is supposed to say.
• The sentence Typically, all elements are arranged at approximately a one-quarter-wavelength mutual spacing, with directors progressively shorter than a half wavelength to couple signals of increasingly higher frequencies onto the dipole. is total rubbish. The directors need to be shorter even for use at only a single frequency.
• The sentence says a quarter wave spacing, the diagram a tenth of a wavelength.
• Talk of 15 and 20 meter bands is not professional.
• Many of the references are to poor sources. ham-shack.com and what-is-what.com are not in my opinion sensible references. There are plenty of good books written about this subject. One fairly good one was published by the ARRL, but was a lot more technical than most of the rubbish in ham journals.
• No mention is made of the fact that the physical length of the elements must be shorter than the electrical lengths.

The article is flawed in too may ways to list really. If this was a device not used by amateurs, then it would have been written in a completely different way. The fact it used by amateur radio operators (hams) means it is obviously attracts edits from hams, and some of the content needs to be understandable by them.

I'd personally like to see the name changed to Yagi-Uda, as it is known professionally. Yagi has taken almost all of the credit for this in the eyes of the public, yet Uda done more of the work. The reasons for it often being known as a Yagi are stated, but I believe personally it should be renamed.

My understanding is that the correct terminology is 'Yagi-Uda array', not antenna. Can't find a ref, though. Was in a radio-engineering text book. 2001:44B8:3102:BB00:18C:A1DE:545B:36AC (talk) 20:18, 2 November 2017 (UTC)

I'm reluctant to try to clean this up, since I suspect 90% of the current editors of the page would hate me for it.

There might be some merit in having a section with a title something like Use in amateur radio and keep some of the more basic things there.

The Yagi-Uda antenna is more complex than the dipole, yet a comparison of the two articles shows the dipole is written in much better detail.

I'm trying to see this from two points of view. I am a ham, and have used Yagis on 2m. I also took a specialist course in Antennas and Radar as part of an MSc. degree in microwaves and optoelectronics.

I'm going to rate this as poor. Drkirkby (talk) 08:56, 18 October 2009 (UTC)

I agree with Drkirkby, much can be done to improve this article but I think improving Wikipedia is more important than hurting egos. I would therefore like to urge Drkirkby or any other knowledgeable users to jump in and start correcting where they can. Skaapgif (talk) 17:30, 24 May 2010 (UTC)

scale drawings

It is easy to locate online DL6WU ARRL k7mem javascript yagi calculators, and downloadable programs and spreadsheets. But they all seem to just generate numbers. Are there any custom generators of yagi layout scale drawings, html pdf jpg etc? For smaller indoor antennas 1:1 scale plots would be very useful, since anyone could just cut pieces of coat hangers and tape them to cardboard to assemble most of the antenna! -71.174.188.137 (talk) 20:02, 12 May 2010 (UTC)

This article contradicts itself in too many ways

In the diagram it says the reflector is .55 x wavelength longer while in the first paragraph it says 5% longer and shorter. Those are different by a little. Later, in the next paragraph, it says "all elements are typically placed a quarter of a wavelength apart" while the diagram shows them as being a tenth of a wavelength apart. Those are different by a lot. Daniel Christensen (talk) 09:08, 29 September 2010 (UTC)

Use as television antennas?

TELEVISON ANTENNAS MAY HAVE BEEN YAGI IN EARLY DAYS BUT ARE MOST COMMONLY LOG PERIODIC DIPOLE ANTENNAS https://en.wikipedia.org/wiki/Log-periodic_antenna THIS ARTICLE IS VERY WRONG AND MISLEADING — Preceding unsigned comment added by 107.3.141.164 (talk) 00:18, 22 September 2019 (UTC)

I think I know something about antenna theory and about yagis. But I repeatedly run into claims that directional TV rooftop antennas are often yagis, as is repeated in this article. I simply cannot believe that, due to the narrowband characteristics of yagis compared to the very wide frequency range of either the low or high VHF (or the UHF) TV bands. The bandwidth of a yagi wouldn't even cover the full bandwidth of a single TV channel! I know that bandwidth is increased by using thick elements, but not that much. Does anyone have a really good reason to believe that yagis are used as commercial rooftop TV antennas? (Having heard it 1000 times doesn't count!). I know that some, but I suspect all, are actually log-periodic dipole arrays (which ARE very wideband!) Interferometrist (talk) 16:10, 1 April 2011 (UTC)

I know live audio reinforcement more than broadcast, but I should think the TV reception antennas would be log periodic dipoles much like the Shure UA870X that I use to pick up wireless microphone signals between FOH and stage. Log periodic dipoles have a fairly wide bandwidth; same as desired in television. I don't have any sources. Binksternet (talk) 17:18, 1 April 2011 (UTC)

Well I did a little research on Google to see what I would find if I were trying to buy a TV antenna over the internet, or other things written about them. And indeed there is a lot of poor and sloppy information, but the antennas (with a few exceptions) are not Yagis at all on closer examination even though they may have included that word in their general advertising. The ones that look anything like yagis are indeed log-periodic dipole arrays (LPDA). One was called a "LPDA-Yagi" so I looked closely and it was a LPDA for UHF TV with some Yagi directors on the front to assist the upper frequency range. And it was possible to buy ACTUAL Yagis but, as we were saying about the narrow bandwidth, you had to order it for a SINGLE VHF TV channel! (And they made ones for UHF where they divided the UHF TV range up into about 8 subbands and you could order one that would work over such a frequency range). So there might be people in very fringe areas who need to pick up a single channel from the nearest city and the Yagi could give them a lot more gain, but for a second station they'd need to buy a second antenna. Some of the other antennas included a plane reflector with a phased array of up to 8 dipoles, and ones based on a corner reflector. But as I suspected, almost all of the directional TV antennas that might have been confused with a Yagi were not, they were LPDA's. So knowing that I will know to change those mis-statements in WP articles where I run across them.

By the way, I find it surprising that the Shure antenna (I looked it up) is a log-periodic when in fact it was only using a narrow band (the only point of log-periodic antennas was to be very wideband). Perhaps they just made one model which could then also be used for other devices at different frequencies. The last time I was involved in sound reinforcement (long ago before I went back to grad school) every mike plugged into a big connector box with a huge cable, a "snake" which went all the way back to the soundboard. I remember hearing about wireless mikes which weren't considered reliable and even a wireless snake, but didn't stick around to ever see one. :-) Interferometrist (talk) 20:40, 3 April 2011 (UTC)

Hmm, that particular Shure model might not be the best example, though it certainly is a popular one. Other log periodic UHF microphone antenna models can be found with wider frequency range, around one octave—a doubling of frequency from bottom to top. There's an Audio-Technica model that goes from 440 to 900 MHz, an Audix model that covers 470 to 870 MHz, the Sennheiser A2003-UHF which stretches from 450 to 960, the Shure PA805SWB from 470 to 952, and the Shure PA705: 620 to 870 MHz. I pick antennas that are sensitive to narrower bands than these when I have a difficult RF environment to work with, so that my RF front end is not fighting through so many stray signals. The wider wideband antennas are handy for the generalist. Binksternet (talk) 21:13, 3 April 2011 (UTC)

OK, it was just that I was looking at a web page describing that model (maybe not the best place) and it mentioned using it over a 6MHz band at 800 something MHz which is quite narrowband, not a reason to use a LP antenna. But now you're mentioning wider frequency ranges. As I said, I have no knowledge about wireless mikes or how you're using them. Are you saying that there are a bunch of mikes on stage each at a different frequency (but nearby frequencies?) and that you aim a LPDA from the soundboard toward the stage to pick up all of them? Using one receiver, or multiple receivers fed from the same antenna? What about getting the mixer output to the power amps near the stage (if that's where they are) and the monitor signals to the stage, is that another wireless system altogether then?

Anyway, I don't know what frequencies are used by these mikes but now you're mentioning antennas that do work over a surprisingly large frequency range. As they should if they are LP. But I can't help but noticing that these are similar to the TV UHF band. Are you sure that these aren't just UHF TV antennas that have been repackaged (and surely jacking up the price!) for this application? The one you have: about how long is it and how many elements? If it goes down to 450MHz then its longer elements should be about 30cm wide and the length of the antenna (and number of elements) will be greater for more gain, though in this case I don't see why you would really need gain (are the mikes' transmitters weak?) or directionality (too much and you couldn't cover the whole stage at once, if that's what you're trying to do). But most LPDA's are just weakly directional, but mainly wideband. If you only needed a narrowband, then a simple dipole or 2-element Yagi would seem a better choice.

Now on to a different subject. Since you're in the field could you please look at http://en.wikipedia.org/wiki/Talk:Vacuum_tube#Vacuum_tube_mike_preamps_--_why.3F.3F and comment if you have an opinion. Thanks! Interferometrist (talk) 23:44, 5 April 2011 (UTC)

Got your tube answer in, but I hedged.

About LPDA antennas: yes, they are aimed at a number of wireless microphones which send a very narrowband signal and which tried historically to slot themselves in between the UHF TV signal components. After recent FCC changes for the USA, fewer frequency bands are legally available but they are not clogged with analog TV signals. The wide-range antenna picks up a bunch of microphone RF signals that are around 5 to 10 milliwatts, and sends them to a receiver distribution amplifier which then sends this amplified mass to the individual microphone receiver front ends. Those front ends focus on the narrow region of interest and pick out the desired microphone signal. I like to make it easier on the front end by giving it more of what it wants; a task accomplished by narrower antenna designs such as dipoles and narrow band LPDAs. Binksternet (talk) 02:01, 6 April 2011 (UTC)

Here in the UK, the vast majority of broadcast receiving aerials are Yagi. Log-periodics are sometimes seen for UHF where that type's advantages (wide bandwidth and high front-to-back ratio) are needed in preference to the relatively low gain, but in most areas all you will see on roofs are Yagis of various types. Since most areas' channels are "grouped", wideband aerials are not normally required, though even these are Yagi.

We don't use VHF for television; Yagis for Band II (FM radio) and Band III (DAB) are designed to cover the entire band.

See http://www.aerialsandtv.com/aerials.html for a discussion on the various types. G7mzh (talk) 15:20, 15 April 2011 (UTC)

Hi, thanks for the comments and info. My previous web searches (above) naturally picked up mainly US sites, so I did another restricted to the UK (I hadn't realilzed that VHF television isn't used there). However based on that research my conclusion hasn't changed much, although the page YOU point to indeed DID discuss some Yagi antennas designed for a portion of the UHF band (not too different from what I mentioned in terms of the 6 or 8 Yagis sold for portions of the American UHF band which I think is a bit wider). And there were also some other antennas on that page that looked more Yagi-like than LPDA-like but weren't called either. However outside of the page you pointed me to, I didn't really find anywhere in the UK to buy an actual Yagi TV antenna..... but let me elaborate.

THIS one is called a Yagi and claims a 2:1 bandwidth which is way beyond belief:

http://www.moonraker.eu/TV-and-FM-Radio/TV-Uhf-Antennas/SUPER-18-YAGI-ANTENNA

No detailed specs are supplied but it mentions a gain of 12-13.6dB (consistent with an 18 element Yagi) but no details. It MIGHT be the same as the one I had seen earlier which was a UHF LPDA (which couldn't have had so much gain) that included a few directors (thus making it a Yagi -- not!) to help at the highest channels. Now this one only claims to be "Yagi style" and has even less detailed info:

http://stores.ebay.co.uk/Capital-Stores-Ltd/TV-Accessories-/_i.html?_nkw=yagi+antenna&_sacat=61394&_sid=104226305&_trksid=p4634.c0.m322

OK, I DID find an actual Yagi in the UK but this was 1) For the FM band and 2) Sold for broadcasting (presumably at a small or pirate station since it only accepts 800 watts):

http://www.broadcastwarehouse.com/label-/aky3/aky5-fm-yagi-antenna/59/product

Now the FM band is 20% wide which defies the conventional bandwidth of a Yagi (~5%). I do tend to believe (but this is hard to find in print) that Yagi's can be made wider band (conventionally with thicker elements, but further....) so this is not preposterous, though I still wonder if someone broadcasting with this wouldn't have it tuned to frequency. It claims SWR<1.35 over 88-108MHz which I really DON'T believe. The A-group Yagi antenna on the page you pointed to shows a gain within 3dB of peak over UK channels 25 - 40 (503 - 623 MHz), again a 20% bandwidth. It fails to mention the SWR change which would make it get more than 3dB worse when used for receiving (a transmitting antenna would usually have a matching device to tune it to the station's frequency so it would be less important then). As I said the Yagi's I found for the US VHF channels (intended for a rather select group of buyers) claimed to work for a SINGLE TV channel only (surely the upper VHF ones could work over 2 channels, 12 MHz, but you order it for the exact one you want to receive). This is all more believable. So are the Yagis sold in the UK for DAB which is a narrow band, among other narrowband apps such as CB.

So in summary I'm still puzzled as to whether a "Yagi" can work with a 20% bandwidth. But EVEN if so, most people (including in the UK) need a wider bandwidth if they are just looking for a "TV antenna" and indeed I didn't find Yagi's sold in the UK beyond what I just reported (of course I didn't search all day long, but as long as the average shopper would). You repeated what everyone else says, the conventional wisdom, found on several Wikipedia articles (for now....) but not backed up by either theory or Google shopping results. Thanks for your input though, -- Interferometrist (talk) 16:06, 18 April 2011 (UTC)

Now I'm puzzled. If they're not Yagis, what are they? Admittedly, there are some wierd and wonderful designs that owe more to art than electronics, but they still follow the basic system of reflector - dipole - directors. Bandwidth can be altered by tweaking the length and spacing of the elements. In the old days of VHF television, aerials were generally single-channel (channel width 5MHz), since only one transmitter per band was available in most areas. (Which is why the old "ITV aerials" (Band III) won't work for DAB). G7mzh (talk) 19:47, 13 May 2011 (UTC)

Yes there is no question that Yagis have been used for television reception involving narrow bands (thus only 1-2 VHF or several UHF channels covered by one antenna). And that they are still available (as I pointed out) for special applications: I imagine that would include rural areas where a single VHF channel needs to be received with more gain than a LPDA supplies, and also for a repeater (or more likely a cable service) needing good reception of a single channel. But these exceptions do not include the average home with a roof antenna.

Yes, I am also puzzled and I do not claim to know what they are selling. To me the distinction is whether an antenna (regardless of its appearance or specifics) relies on electrical connections to multiple elements, or tuned parasitic elements. I consider the latter to be a "Yagi" of some sort, and cannot be very wideband. From browsing the web in search of the elusive Yagi TV antenna, what I have seen are:

• UHF LPDA antennas with added directors for the highest frequencies only, thus they become a bit "Yagi" at those frequencies only
• Antennas with a vertical corner reflector composed of horizontal elements. These could replace the single "reflector" element of a Yagi, but when they are part of a different sort of antenna, then no.
• Antennas which are long with shorter elements toward the front, and these are not properly characterized nor is it obvious from their pictures how many elements are fed.

I can only assume that any antenna with a bandwidth >20% is not a Yagi since I have not anywhere seen that Yagis can be made so wideband, and if that were not true then I would be interested in finding out about it myself and would write it into the article. Until then, though, and with lack of any very concrete evidence that home rooftop TV antennas sold are actual Yagis, I have to conclude (and Wikipedia in fact demands) that conventional wisdom about them being called Yagis not be repeated. But any additional information that you or anyone can add to these observations is highly welcome! -- Interferometrist (talk) 14:18, 14 May 2011 (UTC)

So all Yagis are beams, but not all beams are Yagis? (Not counting logs). Maybe someone ought to write a decent article at Beam antenna and separate it from Directional antenna. Sadly, I'm not in a position to do so. G7mzh (talk) 21:46, 7 June 2011 (UTC)

If anyone is still interested, those antennas referred to above are all Yagis. Although a basic Yagi has a narrow bandwidth of <5%, from what I understand, the UHF Yagi TV antennas shown above use verious techniques to broaden the bandwidth. The excellent website referred to above:

http://www.aerialsandtv.com/aerials.html

shows most of the techniques, although it doesn't really explain them. About 1/3 way down the page, under "Yagis, Double Yagis, Tri-Booms, and X-Beams" there is a block of four pictures, showing a "conventional", "double Yagi", "Tri-boom", and "X-Beam" antenna, that are good examples of the techniques used:

• Thick elements The elements in all the UHF Yagis are generally thick and stubby, having a smaller length/diameter ratio than other Yagi antennas, and this increases the bandwidth (BW). This is particularly noticeable in the "conventional" Yagi (upper left). In addition many have folded dipole driven elements. By itself the folded dipole has a BW of an octave; in a Yagi it wouldn't have that much, but it would broaden the BW. substantially.
• Corner reflectors All the UHF Yagis have corner reflectors, some quite a bit bigger than the parasitic elements. This is a major source of wide BW. A corner reflector antenna can have a gain of 10-15 dBi over a wide BW. I have heard these antennas really act as two antennas; a wideband corner reflector that covers the lower end of the band, and a Yagi that provides extra gain at the upper end where it is needed.
• Multiple Yagis The "double Yagi" (upper right) and the "Tri-Boom" (lower left) have multiple Yagi arrays that are tuned to different portions of the band, giving the combined antenna wide BW. The "double Yagi" is really two Yagis side-by-side; each parasitic element is two rods insulated from each other in the center. The "Tri-Boom" is three Yagis.
• X-Beam The elements in the "X-beam" antenna (lower right), driven and parasitic, are "bowtie" ("butterfly") dipoles made of a pair of V-shaped elements. These same type of elements are used in reflective array UHF TV antennas; their wide BW is enough to cover the band.

--Chetvorno^TALK 02:44, 23 September 2014 (UTC)

The article is not comprehensive enough.

Nowadays, Wikipedia is synonymous with quality information on the web. The article about Yagi-Uda antenna is not self explanatory. An average reader like me had to branch out to several other pages to understand the working completely. I find the "for dummies" books really enjoyable. If only the articles her were written in that way, life would be a lot easier. — Preceding unsigned comment added by N sanjay n (talk • contribs) 08:44, 28 August 2011 (UTC)

Analysis - confusion - edit needed

In the 2nd paragraph (as of Jul 16, 2014) of the Analysis section, the parasitic element (director) and the driven element are taken "for now" to be the same length. In the next paragraph, it is claimed that the director is shorter than the driven element and this 'explains' certain features of the Yagi. You can't have it both ways. You can't explain the theory by assuming equal lengths, then explain other features assuming different lengths...at least not without a clear explanation of why you can hold two contradictory models at once (before breakfast?).Abitslow (talk) 22:05, 16 July 2014 (UTC) A user has been defacing this article repeatedly, and they appear to be registered. If possible, the user should be warned and the page should recieve a lock (confirmed protection or extended confirmed) — Preceding unsigned comment added by Gadgetboy456 (talk • contribs) 11:15, 2 February 2019 (UTC)

Names Yagi and Uda

Chapter 11 in the ARRL Antenna Book (copyright 2003) confirms this article's statement that Uda "did much of the development work." But it states that Yagi introduced the array to the world outside Japan through his writings in English. It may be referring, at least in part, to a patent, but this isn't stated.

Pretty much everybody calls them Yagi antennas. "Yagi-Uda" may be better at crediting Uda's work, but it's not the name people actually use. Geoffrey.landis (talk) 18:59, 20 July 2020 (UTC)

A physically consistent model of the passive radiator - changes of September/October 2021

This is to explain the editing of September/October 2021. I did some intense research in the older literature trying to find a clear and consistent explanation of the passive radiator under far-field conditions. I am currently working on a paper on an antenna that uses passive radiators at some distance and wanted to find a clear conceptual explanation (before introducing mutual impedances), but this seems to be difficult to find. The best reference I found is the RWP King book (one has to interpret the formulas given on the cited page) or H.Zuhrt, Elektromagnetische Strahlungsfelder (1953, in German).

I found the previous "Theory of Operation" section mostly incomprehensible, as it was physicaly wrong due to its implicit assumption of excitation of the passive radiator without taking any electromagnetic propagation between driven and passive elements into account. In addition, the argument was based on a voltage excitation of the passive antenna, but half-wavelength dipoles are excited by a current. Therefore I deleted this and replaced it with a correct explanation (which took some time, because the problem is really quite difficult). To make sure that I was not missing any signs, I checked all the explanations with 3D simulations in HFSS. Sometimes the formulas are easy to misinterpret, as in the usual cartesian and spherical coordinate systems E_z and E_theta point in opposite directions in the xy plane, so a minus sign may easily be missed (which would change a 90° lagging phase to a 90° leading phase). Zuhrt and King clearly show that the current on the passive element (when it is at resonance, so that its self-impedance is real) is in phase with the incident electric field and the simulations support this! This shows that most of the explanations that I deleted were indeed wrong.

Now we have to understand where the phase differences between incident radiation and reradiation come from. Here, the diagrams in the "Analysis" section may be easily misleading. We have to distinguish between the near field amplitude (which is never shown) and the far field amplitude, which is drawn also in the diagrams in the "Analysis" section. The far-field amplitude is given as

${\begin{aligned}E_{\theta }&=\zeta _{0}\,H_{\phi }=i{\frac {\zeta _{0}\,I_{h}\,L\,k}{4\pi \,r}}e^{i\,\left(\omega \,t\,-\,k\,r\right)}\,\sin(\theta )\end{aligned}}$

(see dipole antenna - short dipole). As E_theta points into the opposite direction as the current, we have to add a minus sign when comparing the phase of emitted field (in z direction) and exciting current (in z direction). The exponential describes the propagation delay between current and field and, in effect, we have an additional 90° lagging phase offset due to the factor -j. So the theory shows clearly: there is no phase offset between the incident electric field and the current in the passive element excited exactly at resonance. The 90° lagging phase that we observe in the reemitted field is a result of the excitation of the radiation field at the dipole.

If the dipole is shorter or longer that the resonant length, the current will receive a phase shift with respect to the incident field (or with respect to the open-circuit terminal voltage of the dipole)- either a leading phase shift for the shorter capacitive director element or a lagging phase shift for the longer inductive reflector element. The two-step explanation using transmission line theory and reflection at a short termination seems ok (except that it ignored the direction of the current of the reverse wave, which I corrected), so I left it. However, King and Zuhrt also give formulas for the open-circuit termial voltage of a receiving dipole as well as for the current of a loaded receiving dipole, so strictly the explanation could be further shortened by just using the formula for the current with a zero load impedance - but both explanations lead to the same result.

Unfortunately, the diagram for the explanation of the Yagi using a single director is partially wrong. The field emitted by the director is never more than 90° out of phase with the incident field (in the diagram it is 110° out of phase). I tweaked the numbers a bit so that we have physically correct numbers in the text, which are also roughly consistent with the diagram. Maybe someone who is more involved with wikipedia could create a better diagram. In this case I would recommend also to improve the numbers: the current numbers don't actually produce a very pronounced directional effect.

The analysis part discussing mutual impedances is correct. This can be found in many books. As the Yagi-Uda antenna cannot be fully understood without taking mutual coupling into account, most books omit a simplified explanation of the passive radiator under far-field conditions and only discuss the passive radiator on the basis of mutual impedances (e.g. Balanis or Kark).

I am full professor of microwave engineering at a university in northern Germany. I spent a few days in understanding the issue. I also double-checked that everything is correct with 3D simulations and some simple modeling (the results will become part of a lecture on electromagnetic wave theory) - so please consider this before editing or reverting the changes I made. — Preceding unsigned comment added by 90.187.42.73 (talk) 15:26, 7 October 2021 (UTC)

Sunderland

Kudos to whoever added the correct origin of the Sunderlands "Flying Porcupine" nickname. One of the very few places where I have seen that, and not the universal "because it was so heavily armed" nonsense (in spite of it not being much more heavily armed than numerous other aircraft of the period). Even though someone had to reference that myth as well, just out of tradition. Idumea47b (talk) 00:01, 19 September 2023 (UTC)