Talk:Dipole antenna

Two of the same diagram...

Not sure why there are two of the same diagrams:

by user:LP

by user:LP

although neither of them are SVG so I just drew one:

here is the SVG version...

Any objections to replacing both? Anything wrong with my version? No pressure or rush... M∧Ŝc²ħεИ_τlk 19:04, 22 December 2012 (UTC)

These two diagrams should not be the same, nor do they look the same (to me); the differences are explained in the text of the article. The proposed new diagram is (again, to me), less clearly a torus; probably this is a result of the transparency of the surface, and the lack of shading. Nevertheless, it would be an improvement to replace each of the existing diagrams with an SVG version. --catslash (talk) 21:42, 22 December 2012 (UTC)

Yes, I know replacing the images by SVG equivalents would be an improvement - that's the whole point.

Fair enough, if this SVG form is unhelpful then it's unhelpful, and if two seperate ones are needed, then fine, but please suggest how they should be to improve the article. In this one, it was intentionally colourized, and was to show the vertical sections rather than horizontal circular contours. There is shading, but it has failed badly... Should I just trace over the JPG files in SVG form, all black and white? Then possibly add coloured opaque surfaces with clearer shading? M∧Ŝc²ħεИ_τlk 01:20, 23 December 2012 (UTC)

The balun diagrams could usefully be replaced by SVG versions, since they have some flaws which could be corrected in the process. --catslash (talk) 22:19, 22 December 2012 (UTC)

Yes, sorry... I meant to draw these in SVG once upon a time... I'll get round to them... Please list the suggestions/corrections to fix, before I start. Thanks, M∧Ŝc²ħεИ_τlk 01:20, 23 December 2012 (UTC)

Half-wave antenna: 'voltage distribution'

Does the discussion of voltages in the Half-wave antenna section make any sense? It's not clear what the y-axis is in the File:Dipole Antenna.svg graph, since potential difference is not well defined in a non-conservative field unless a path of integration is specified. Perhaps the intended path is a quarter-circle arc from the plane normal to, and through the centre of the dipole, to a point on the conducting element - but this is not stated. The statement: A standing wave on an element of length approximately λ/4 yields the greatest voltage differential is likewise unclear, and the sentence The larger the differential voltage, the greater the current between the elements. is perhaps a misunderstanding. I'm inclined to delete the voltage plot and any mention of voltages - or can somebody explain the intended meaning? --catslash (talk) 19:07, 25 December 2012 (UTC)

Fixed by Interferometrist - Thanks. --catslash (talk) 03:15, 2 December 2014 (UTC)

Element Length

The length of a quarter wave can be calculated simply by two formulas depending whether you wish to use metres or feet:

Quarter wave in feet is calculated by 234/f MHz, and in Metres it is calculated by 71.3/f MHz.

Many people will tell you that you cannot feed a dipole through an - AMU or Antenna Matching Unit - WRONG you can, as many hams will tell you.

Any antenna is resonant at one frequency, transmitting away from that frequency means that your Voltage Standing Wave Ratio rises. If you plot a sine wave for the voltage, on a graph along with a cosine wave for the current you get two waves that represent the phasing of the electrical wave, however it does not show what happens as your VSWR rises. You can easily plot the VSWR curve on the same graph - I use values of 1 to 10 and then plot the TANGENT value of each angle so that you can see how and why a VSWR rapidly peaks and drops and why it repeats every odd multiple of 90 degrees. Adjusting the length of the feeder so that from the AMU is approximately an odd number of 1/4 waves means that a dipole will radiate efficiently.

I work as an antenna designer and also hold my own ham licence and I have demonstrated to many how and why you can feed a dipole via an AMU much to their amazement.

It is only for the design engineer that the complex mathematics creep in, but for the average person the simpler the theory the better.

— Preceding unsigned comment added by user:90.244.53.168 (talk • contribs)

Billboard antenna

What is a billboard antenna? When I click on "billboard antenna" in some other Wikipedia article, I expect to go to an article that at least mentions the word "billboard". Instead, I end up here at the dipole antenna article, which currently never mentions the word "billboard". Is there maybe some other article that mentions "billboard antenna" that the redirect should go to instead, or does this article need to say a few words about "billboard antenna"? --DavidCary (talk) 16:06, 14 May 2014 (UTC)

See Reflective array antenna. Don't think it's a very common term though. --catslash (talk) 17:55, 14 May 2014 (UTC)

I've changed the target of the Billboard antenna redirect page from Dipole antenna to Reflective array antenna. --catslash (talk) 18:04, 14 May 2014 (UTC)

Thank you, catslash. --DavidCary (talk) 15:59, 21 May 2014 (UTC)

5.12 dBi perpendicular to the antenna axis,

What is 5.12 dBi? What is a dBi. Is that decibels of the current ratio? If so, what is the numerator and what is the denominator? WithGLEE (talk) 13:17, 9 October 2014 (UTC)

As the article antenna gain makes clear in its introduction, dBi is decibels isotropic, the ratio of the signal power radiated by the dipole in the direction of its main lobe to the signal power produced by an isotropic antenna, which radiates equal signal strength in all directions. It is the usual units used to express antenna gain. --Chetvorno^TALK 19:50, 9 October 2014 (UTC)

And I got the figure wrong. The figure that was in the article, 5.12 dBi, was for a quarter-wave monopole, not a half-wave dipole, which is 2.16 dBi. My bad. Thanks for catching that. --Chetvorno^TALK 20:06, 9 October 2014 (UTC)

Hertzian Dipole µH

In the Hertzian Dipole equation for µH, why isn't the µ subscripted with 0? Jim Bowery (talk) 20:36, 23 August 2015 (UTC)

Merge Doublet antenna here?

This is another term for a dipole antenna, and the Doublet antenna article is almost a stub. --Chetvorno^TALK 06:50, 4 September 2015 (UTC)

Done --Chetvorno^TALK 22:18, 16 November 2015 (UTC)

Feedpoint not always in center.

There seems to be a focus on feeding the dipole in its center despite the IEEE definition of a dipole antenna not dictating such feed placement. To wit...

"dipole antenna (antennas). Any one of a class of antennas producing a radiation pattern approximating that of an elementary electric dipole. Note: Common usage considers the dipole antenna to be a metal radiating structure which supports a line current distribution similar to that of a thin straight wire so energized that the current has a node only at each end. Syn: doublet antenna."

An additional definition is found in the EIA/TIA-329-B...

"A dipole whose electrical length is half a wavelength and is formed by a straight metallic radiator, one-half wavelength long, whose diameter is small compared to its length, so energized that the current has two nodes, one at each end, producing maximum radiation in the plane normal to its axis."

The dipole is defined more by its function, than form. It can be fed in the middle, end or anywhere in between and doesn't necessarily have to be two conductors as the text currently suggests (think J-pole). crcwiki (talk) 17:22, 28 April 2016 (UTC)

UPDATE Jan 13, 2017 - Reading no objections, I added language to the main article confirming the notion the dipole is not defined by form, but by function per the IEEE definition reference above. It is very important to not lead readers astray thinking, for example, the position of a feedpoint has anything whatsoever to do with the definition of a dipole antenna. crcwiki (talk) 19:43, 13 January 2017 (UTC)

References

Severe lack of references to back up content

This article is woefully short of references and some sections have none. Unless the points made are backed up with external references in a timely matter, I will begin marking problematic sections as Unreferenced or Refimprove. I will do my part to search and insert references, but in the mean time viewers need to be made aware of the missing and required references. crcwiki (talk) 17:31, 28 April 2016 (UTC)

UPDATE March 1, 2018 - Adding banners reflecting the lack of primary inline citations through this article.crcwiki (talk) 20:14, 1 March 2018 (UTC)

Animated graphic incorrect

The animated graphic purporting to show "the sinusoidal standing waves of voltage (V, red) and current (I, blue) on a half-wave dipole driven by an AC voltage at its resonant frequency" is very nice, but it is incorrect in that it shows the voltage and current 90 degrees out of phase. Voltage and current are of course always in phase in a resonant antenna (a purely resistive load).

I am not going to change this, since I lack the graphic skills as well as the credentials, but I would be interested to hear what one of Wikipedia's EE contributors has to say about it. Hopefully someone in authority will bring this to the attention of the right editors so it can be addressed by modifying the graphic; it would be a shame to do away with it altogether. — Preceding unsigned comment added by 107.77.222.209 (talk) 00:05, 20 May 2016 (UTC)

The graphic is correct. The misunderstanding arises from the misapplication of the statement " Voltage and current are of course always in phase in a resonant antenna (a purely resistive load)". The load seen at the feed point will be resistive in a resonant antenna (at the exact resonant frequency), and any energy being fed into the dipole will be composed of in phase current and voltage. However, the energy STORED in the antenna (and any resonant circuit) is stored in electric and magnetic fields which are continuously "sloshing" back and forth. In a high Q circuit the stored energy will dwarf the energy being added and lost. It is this stored energy that produces the current and voltage that is shown in the graphic. Energy is conserved. If the energy being added fro the source and that being radiated away equal each other, and if these are small compared to the stored energy, then we know that the energy stored in the electric field will be proportional to the square of the voltage on the ends of the dipole. The energy stored in the magnetic field will be proportional to the square of the current in the center of the dipole. For the total energy to be constant, the current and voltage MUST BE OUT OF PHASE. At one moment all the energy is in the magnetic field, 90 degrees later it is all in the elecric field. At any other moment it is shared but the total is not changed. This applies to all resonant circuits, not just a dipole. I hope this helps. — Preceding unsigned comment added by JNRSTANLEY (talk • contribs) 11:18, 20 May 2016 (UTC) JNRSTANLEY (talk) 13:45, 19 July 2018 (UTC)

The graphic may be correct in that it shows the 'circulating' energy stored in the resonant dipole, and the idea that the applied energy from the source tops up the stored energy at just the right time to keep it oscillating may also be clear, but the section in the article has Impedance in the title and it talks about impedance, and the graphic is under the same section, so when a normal person tries to relate impedance to the voltage and current in the picture, even if just for the fact that they are near each other in the article, it's very unclear if the voltage and current in the graphic are the conditions which actually determine the impedance seen at the feed point. So perhaps the article could in addition describe how the applied RF energy at the feed point relates to the incident and reflected waves at the ends of the antenna, how these result in standing waves, and the conditions of voltage and current and the phase relationships which determine the complex impedance for each point on the antenna. If the half wave dipole were compared to the last 1/4 wave section of an open circuit transmission line this would make it a lot easier to understand.

I drew the animation. I didn't draw it for this section but for Antenna to illustrate for general readers what a standing wave on a dipole looked like, so I didn't make it exactly mathematically correct. The determination of the exact current and voltage waveforms is complicated, because the antenna is losing energy as radiation along its length. Nobody caught the most obvious error: that the voltage is shown as a simple sine wave which goes to zero at the center. Since the feedline applies an oscillating voltage there should be a voltage step at the feed point. It is the voltage step applied by the feedline that must be in phase with the current, not the total voltage standing wave. I don't have time to change it now. I think the solution is to move the image to somewhere else in the article so people reading the "Impedance" section won't be confused by it. --Chetvorno^TALK 07:13, 29 June 2020 (UTC)

 Done --Chetvorno^TALK 07:30, 29 June 2020 (UTC)

Chetvorno, for a resonant half wave dipole the standing waves of voltage and current on the antenna are in phase in time. The animation clearly shows that the two wave forms are 90 deg out of phase in time. To understand from a graphical image the idea that there is no reactance present at the feed point because voltage and current there are in phase, the animation should show the two waves varying together in phase in time, especially if the animation is under the section entitled 'Impedance'. Animations like these are the first thing that people look at when they access an article like this. One correct animation can explain everything. Maybe there should be two animations, one for stored energy and one for standing waves of voltage and current. Placing that animation which shows stored energy in the 'Impedance' section is very confusing because the animation is not really relevant to the section. This is really simple, it just needs the same animation with the correct phase relationship between the waves and then it all makes sense. Also, the difference between wave impedance and feed point impedance could be explained, so that readers know that the wave impedance does not determine the impedance seen at the feed point.

No. Read JNRSTANLEY's post above. The dipole functions as a resonator, the stored energy is a lot larger than the energy added each cycle by the feedline. In a traveling wave that carries power the voltage and current are in phase, but in a standing wave like we have here, which doesn't transmit power but just stores energy, the voltage and current are 90° out of phase. You can see that the voltage and current have to be 90° out of phase at the ends of the antenna by looking at a short length of conductor at the end. Since the current can't go anywhere it acts as a capacitor. If its capacitance is C, $i=CdV/dt$ so if $V(t)=V_{0}\sin {\omega t}$ then $i(t)=\omega CV_{0}\cos {\omega t}=-\omega CV_{0}\sin {(\omega t-90^{\circ })}$. Since the antenna is radiating power the phase along the rest of the antenna differs slightly from 90°, but as in a high Q tuned circuit, not much. At the feedline there is a small oscillating voltage difference or step representing the feed voltage which I didn't include in the drawing. If the amplitude of the feed voltage is $V_{\text{in}}$ the amplitude of the voltage at the ends of the antenna will be $QV_{\text{in}}$. Since the Q of dipole antennas is usually over 10 the feed voltage is small compared to the voltage standing wave which is why I didn't include it. It is the feed voltage that must be in phase with the current in the antenna at resonance. --Chetvorno^TALK 17:51, 3 July 2020 (UTC)

The fact that the current and voltage standing waves on a dipole have a 90° phase difference is in most elementary antenna books; here are some sources: [1] p.134, [2], [3], [4], [5]. --Chetvorno^TALK 19:01, 3 July 2020 (UTC)

Chetvorno, thank you for the reply and your effort. Yes what you say does agree with all the antenna books around that i have read also. The problem is that no one understands this and most antenna books are not very good at explaining this topic. The misunderstanding is this : it is very hard to see which waves are in phase and which waves determine the feed point impedance. If the standing waves in your animation are the actual physical voltage and current on the antenna, it is difficult to see how these standing waves do not determine the reactance at the feed point. I myself do not understand still how the incident wave from the feed point and the reflected wave add to produce the total reactance at the feed point when these waves can't be seen or measured even though every one knows they are there. It is the phase relationships between the original applied AC, the incident wave at the end, the reflected wave, and the standing waves of voltage and current, and how these various things relate to the complex feed point impedance that needs further explanation and clarification otherwise normal people cannot work out what is going on because all the information is not there. Also wave impedance should be explained in my opinion. I hope what i say makes some sense. — Preceding unsigned comment added by 203.122.143.146 (talk) 02:27, 4 July 2020 (UTC)

I agree it's confusing. I have no education in antennas, and only a little experience, I'm just figuring it out like you. I'm drawing up a more accurate animation showing the waveforms including the feed voltage. One thing that makes it confusing is that in the animation the voltage waveforms are not referenced to one side of the feedline but to the "center" of the feedline. If the two antenna elements are considered transmission lines, referenced to a "ground" somewhere, the feedline is feeding them differentially, so for that reason the impedance across the feedpoint is not the same as the impedance that would be seen driving a single element from ground. I know the antenna functions as an underdamped lossy resonator, driven at resonance. In most dipoles the ohmic resistance of the elements is small, and most of the loss is due to the radiation resistance, which acts exactly like an ordinary resistance distributed along the elements. This is the really difficult thing to calculate, but in a half wave dipole it is equal to 73.1 ohms. The capacitive and inductive reactance must be much larger than this. I'm pretty sure that like a transmission line the waveforms can be calculated from the Telegrapher's equations, but I don't know how to calculate the capacitance and inductance per unit length of the rod. --Chetvorno^TALK 20:48, 4 July 2020 (UTC)

Chetvorno, thank you again for the reply. I am very happy that you are redrawing the animation. Please let me describe a couple of questions which are often not explained well in antenna books and if Wikipedia addresses these in an explanation of dipole operation then i think it would be a big step in the right direction in clearing up confusion for many. 1. It's obvious that the element lengths determine the resonant frequency, what determines feed point reactance, do the standing waves determine feed point reactance or is it the incident and reflected waves ? The standing waves cannot determine the feed point reactance because they are 90 deg out of phase and the feed point at resonance would then be (73 ∟ 90º), and how can the incident and reflected waves on the antenna determine the feed point reactance if they can't be measured because they got added together to produce the standing waves ? 4. Why doesn't wave impedance have a reactance ? 5. What's the difference between wave impedance and feed point impedance ? 6. How does the stored circulating energy relate to the original incident and reflected waves ? 7. Why even bother with resonance, excluding transmission line / antenna mismatch, does a resonant dipole work better and why ? Is it like a tuning fork ? 7. When waves are talked about, there is one original incident wave emanating from the feed point and then one wave reflected back from the ends, and these waves have a voltage and a current, and so you can plot the voltage and current distribution, but the voltage and current waves are not waves on their own, they are characteristics of the wave of energy which is really movement of displacement of electrons ? 8. What is the voltage measured with respect to ? 9. The distinction between the instantaneous values of voltage and current and the 'averaged over time' RMS value is never made. 10. A large animation showing the applied AC wave form at the feed point, the wave traveling along the antenna from feed point to end, the reflected wave, the standing waves, and the electric and magnetic fields would be super, amazing and awesome :) especially if it's all referenced to the applied RF at the feed point in a very obvious way so you can see what happens during one cycle. I hope everything i say makes sense.

Old animation

New animation

@203.122.143.146: Thank you so much for the detailed list of questions above! Feedback like this really helps to know how the existing article should be improved. I don't know the answer to all of your questions, and this page is supposed to be for discussions about improving the article, not general discussion of dipole antennas. However I've felt for years this article is inadequate and needs to have an explanatory section, which should address these questions. I think you're going to be disappointed at the new dipole animation; since the Q of a dipole is fairly large the driving voltage is just a small perturbation of the standing wave, so it's not much different from the previous animation. By the way, you can sign your posts by typing four tildes ~~~~ after them, this helps other editors see who is making the comment. --Chetvorno^TALK 15:17, 9 July 2020 (UTC)

@JNRSTANLEY: @107.77.222.209: @203.122.143.146: Okay, I have (at great personal sacrifice, groan, whinge) drawn an improved animation Dipole antenna standing waves animation 3-10fps.gif which corrects the omission in my previous animation Dipole antenna standing waves animation 1-10fps.gif, showing the effect of drive voltage on the standing waves. It is in the article section on "Half-wave dipole". You can see there is a sinusoidal voltage step $V_{\text{i}}$ (diagonal line) at the feedpoint, which is in phase with the current, so the impedance at the feedpoint is resistive. This provides the energy which is lost in the radiated radio waves. The waveforms shown are probably close to the waveforms in an actual dipole, at least qualitatively. I'd like to add that no antenna textbooks that I know of provide this level of detail, all just show graphs of the undriven standing waves shown in my old animation. --Chetvorno^TALK 15:17, 9 July 2020 (UTC)

Chetvorno, thank you once again for the reply and your excellent efforts. I think confusion still exists however. Your new animation is on the right track i think but it still doesn't show the in phase voltage and current (due to resonance) at the feed point. At any one point on a resonant half wave dipole there can only be one electric potential and one value of current at any one instant in time. For a resonant half wave dipole as everyone knows the voltage and current at the center feed point terminals are in phase. There cannot be in phase voltage and current at the feed point and then at the same two points on the inner ends of the dipole elements 90 deg out of phase standing waves. Your animations are self contradicting in that they show there is in phase current and voltage at the feed point and at the same time 90 deg out of phase standing waves also at the feed point, it doesn't make any sense. After all this time i still haven't found anyone who çan explain this apparent contradiction or explain to me what i am missing. All the antenna book's ive read don't come close and the ARRL antenna handbook is the worst of them all. If anyone reading this can give an explanation it would be very very much appreciated. Apologies if i am the only person confused by this. — Preceding unsigned comment added by 144.130.106.118 (talk) 11:09, 11 September 2020 (UTC)

Sorry but I haven't been following this discussion, but believe I can comment intelligently. First, the original illustration is correct (to the extent that the deviation from reality wouldn't be visible) and the new one is misleading at best (and wrong in scale). The voltage and current current curves are smooth and infinitely differentiable (being essentially a sine wave) EVERYWHERE except at the ends, and for the voltage at the terminals. The one "mistake" in the original figure (but which if corrected wouldn't look any different) is the wrong assumption that the voltage is continuous across the gap, which of course it isn't because that's the terminal voltage. However the (2N 1)/2 wave dipole at resonance has a very tiny feedpoint impedance (resistive) and thus the voltage on either terminal is TINY compared to the high voltages at the ends (where the impedance is huge), so any figure that shows the voltages at the ends would make the feedpoint voltages appear essentially zero, as the original figure CORRECTLY does. Correction of that figure just involves a (rather tiny) STEP of voltage right AT (i.e. across) the feedpoint, which is IN PHASE with the current (for a transmitting antenna) and not dependent on the precise spacing between the two terminals. I guess the new figure attempts to do that, but shouldn't try to depict any specific voltage in between the feedpoints (where there is no metal! I could put some metal there with 723 volts at a different frequency if I wanted!) but simply a small (difficult to see, but ok to exagerate if you say so in the caption) difference between them.

Also note that what I just said goes for the resonant frequency where the feedpoint is resistive. Make the dipole longer or shorter, the sine wave of voltage that peaks at the ends no longer reaches zero at the feedpoint (no longer being 1/4 wave away) and all of a sudden you DO have a relatively large (i.e. not too small compared to the ends) voltage, which is in quadrature phase to the current. THAT voltage in quadrature (plus the small in-phase voltage present even at resonance) divided by the current, gives you the LARGE reactance now seen at the feedpoint in series with the original radiation resistance. Interferometrist (talk) 19:11, 11 September 2020 (UTC)

I drew all the animations. I drew the second as an explanatory tool, since in the original animation (top above) readers kept confusing the standing waves with the drive voltage at the center, and saying the diagram was erroneous because the current and voltage on the antenna should be in phase (see . To that end I exaggerated the drive voltage so it would be visible, so readers could see that it is in phase with the current at the center. That is also the reason I drew the potential graph across the feedline terminals - for visibility; I guess it might be clearer if I remove that portion of the graph, as you suggest. I mentioned repeatedly above that the Q of dipoles is pretty high so the drive voltage is actually insignificant compared with the standing waves. I think this diagram is still useful in the article, as long as we explain in the caption that the drive voltage is exaggerated for visibility. The previous animation (at top) just showing the standing waves, which is found in all the textbooks, does not give readers any concept of how the antenna is driven by the transmitter. --Chetvorno^TALK 19:56, 11 September 2020 (UTC)

Sure, great. One thing though: can you slow down the animation? I find it difficult myself to look at it and move my eye from the voltage to the current fast enough to be a human phase detector! Interferometrist (talk) 20:25, 11 September 2020 (UTC)

@Interferometrist: Oh, okay. When I'm making these things I tend to lose the ability to judge what is a good frame rate.

Thanks for all the great feedback above. The idea that the feedpoint current and voltage are in phase, but the standing wave current and voltage in the dipole elements are 90° out of phase, seems to be a difficult one to get across to readers. I was hoping that this 2nd diagram would clarify things, but readers don't seem to believe the phase relationships in this new animation are correct either (see last post above). Besides the graphical and scale details you mentioned above, you don't have any problem with the phase relationships shown in this animation, do you? For example, in a transmitting antenna, the voltage across the center feedpoint leads the voltage at the ends of the dipole by 90° as shown here, right? --Chetvorno^TALK 21:21, 11 September 2020 (UTC)

Oh yes, it's absolutely right, for a transmitting antenna (which is sort of stated. Did you want to mention in the already long caption that the feedpoint voltage would be reversed when used as a receiving antenna?). It might not look as cool, but I know I would find it easier to verify what you just said if it were 3x slower. And don't show any voltage in between the terminals, since that isn't really defined. But otherwise, yes, great! Interferometrist (talk) 23:17, 11 September 2020 (UTC)

Interferometrist and Chetvorno, apologies for the delay, the mechanisms surrounding a fundamental characteristic of the antenna which is what determines the reactance present in the impedance seen at the feed point is not mentioned at all in the article. A simple explanation would clear up a LOT of confusion regarding this topic. Most Ham radio operators think for example that there are the inductive and capacitive reactances which cancel at resonance and this is why there is zero reactance. This makes me very sad :(

This comment by Interferometrist :

"Make the dipole longer or shorter, the sine wave of voltage that peaks at the ends no longer reaches zero at the feedpoint (no longer being 1/4 wave away) and all of a sudden you DO have a relatively large (i.e. not too small compared to the ends) voltage, which is in quadrature phase to the current. THAT voltage in quadrature (plus the small in-phase voltage present even at resonance) divided by the (******* which current, standing wave current or source current ?? ******) ---> current, gives you the LARGE reactance now seen at the feedpoint in series with the original radiation resistance."

THIS IS THE ANSWER !!! to my main question, what determines the reactance in the feed point impedance. Can you please tell me if i understand this properly ? : at resonance the voltage of the standing wave at the feed point is always zero because it's exactly 1/4 wave length away from the end of the antenna, this standing wave of voltage is always 90 deg out of phase with the source current regardless of the length of the elements, when the length isn't 90 deg then the voltage is not always zero and it is THIS voltage of the standing wave which is out of phase with the applied current from the source and THAT in series with the radiation resistance is what determines the impedance at the feed point. Is that right ?? W0kacheeta (talk) 00:41, 26 November 2020 (UTC)

However Interferometrist's comment seems to be contradictory to JNRStanleys's earlier comment :

You can see there is a sinusoidal voltage step $V_{\text{i}}$ (diagonal line) at the feedpoint, which is in phase with the current, so the impedance at the feedpoint is resistive. This provides the energy which is lost in the radiated radio waves.

Definition of "Voltage"

You don't need metal to have a voltage. There is an electric field between the feedpoint, and at any point that field has an electric potential, measured in volts. I've said it before, now I'll say it again: part of what makes these images confusing is they don't specify precisely what they are illustrating. "Voltage" is anything measured in volts. Is that electric potential difference, and if so, relative to what reference? Electric field potential? 161.97.224.110 (talk) 14:19, 1 November 2020 (UTC)

Well, I have to agree, the animation does not specify what the voltage reference point is, and this has been confusing readers. Dipole antennas, like two wire transmission lines, are balanced loads. From symmetry, the voltage is referred to a "center" potential midway between the voltage on the two feedline conductors. As you mentioned, there doesn't have to be an actual metal terminal at this potential. You can imagine the AC voltage source at the bottom of the drawing split into two sources of half the voltage in series, and the wire connecting them grounded. I'll add something to the caption about this. --Chetvorno^TALK 21:18, 1 November 2020 (UTC)

I don't have any problem with the voltage in between the terminals being shown as a continuous slope from V to -V, which implies a constant electric field in that region. Except to point out that that doesn't have to be the case, I could place a battery somewhere in the space between the antenna terminals and then the voltage between the positions of the two battery terminals would always be 1.5v DC, contrary to the diagram (and the antenna wouldn't be affected). But on the more general point raised by 161.97.224.110, one can NOT generally talk about a unique voltage in between point A and point B except in a DC (static) situation, or where the distance between A and B is much smaller than a wavelength as it indeed is in between the feedpoints, which is why you CAN talk about the voltage being fed to the antenna. But the only reason we can talk about the voltage along the antenna, is because we've agreed to conform to the Lorenz gauge. What is well defined at any point and time is the electric field E, but not how that is divided between the gradient of the scalar potential V and dA/dt due to the vector potential A. This is fixed by agreeing to the Lorenz gauge which stipulates the divergence of A in terms of V. You cannot just ask for a "reference point" for 0v and measure with a voltmeter (or scope) since what the meter measures depends on the geometry of the two leads (since we're talking about points not much closer than a wavelength, they can't take the same net path, like the ground clip right at the end of a scope probe). Pointing all this out in the article would be distracting and showing the voltage as if it were a unique measure without caveats is justified, but the full answer to 161.97.224.110 is that we have agreed to call a certain thing voltage in order to make the mathematics workable, and makes the antenna element look similar to a transmission line. Interferometrist (talk) 16:32, 2 November 2020 (UTC)

Previous discussion

I want to ask one additional question, a very common way of feeding a half wave dipole is to not split it in the center and use a gamma match, this is probably used more than the split in the middle approach, do your comments and the diagrams above also apply to this configuration ? And also how about a folded dipole ? — Preceding unsigned comment added by 144.130.106.118 (talk) 23:16, 11 September 2020 (UTC) Maybe you need two animations, one which shows the seemingly correct out of phase in space and time voltage and current waves which result in the corresponding out of phase in space and time electric and magnetic fields (i believe this is the case), and then another animation which clearly shows the in phase feed point current and voltage, and then some more text which tells the reader this is hard to comprehend and explains this one point of confusion which is "how can the feed point current and voltage be in phase when the voltage and current standing waves at the feed point are out of phase ?". — Preceding unsigned comment added by 144.130.106.118 (talk) 23:28, 11 September 2020 (UTC)

Chetvorno, I would like to point out something else which causes confusion everywhere it seems, and i point this out at a risk because its not entirely clear to me if my understanding is correct. For a center fed resonant half wave dipole when transmitting, because the elements are 1/4 wave long the traveling waves which are reflected from the ends of the antenna arrive back at the feed point in phase with the next cycles of applied RF energy. I believe this is the reason why a half wave dipole is resonant and has no reactance in the impedance at the feed point, noting that the term "half wave dipole" inherently and necessarily implies resonance and there is no such thing as a non-resonant theoretical half wave dipole. The incident and reflected traveling waves on the antenna are in phase with each other. It is the resultant standing waves which are out of phase and which produce the electromagnetic field. The original incident and reflected traveling waves are obscured by the addition of each to the other which produces the standing waves. If what i just said is all correct, then i believe this needs to be explained so it's clear what are the factors which determine the feed point impedance and that it's the standing waves which are shown in your animation and the standing waves determine the wave impedance but not the feed point impedance. Again apologies if my understanding is incorrect and if anyone could comment on errors in my thinking it would again be very much appreciated. If the article explained half wave dipoles better then i wouldn't be as confused as i am. — Preceding unsigned comment added by 144.130.106.118 (talk) 22:23, 12 September 2020 (UTC)

Look, I'm afraid you are mistaken on several points that I don't have time to detail let alone your follow-up questions. But you are trying to oversimplify it but you need to understand that oscillating E, H and J together are simply not much subject to intuitive understanding and you can't even talk about "X causes Y" in most cases. If you're interested I suggest going to a theoretical antenna book first chapter which takes a current distribution, fixes the gauge, and calculates the A field and (voltage) which gives you the waves everywhere. Only the current is important (in a wire antenna. Voltage for a slot antenna) for determining the far field and indeed dipoles of different wire diameters with the same input current have very different voltage scales (and thus impedance at the feedpoint or anywhere else) but almost exactly the same radiation as is presented in chapter 1. It's really only the current that's important for radiation so even showing the voltage pattern is questionable as it only affects the impedance at the center feedpoint as is now correct in the animation (or other than center as you can see). If you want to see how non-intuitive the operation of a simple antenna is, look at the antenna articles' sections on finding the input impedance, Hallen integral equation, and mutual inductance and you'll see this is already getting to heavy for almost any likely reader. Interferometrist (talk) 21:45, 13 September 2020 (UTC)

144.130.106.118: Sorry for the late reply. I think you are on the right track. The standing waves of voltage and current are each composed of two oppositely moving traveling waves, and the traveling voltage waves (but not the voltage standing wave) are in phase with the feed voltage at the center, so the feed adds energy to the antenna. Agree this stuff should be explained in the article. I appreciate your discussions of what isn't clear, as I think it helps in improving the article (as well as helping me get my head round it). Although I've added a few items to the article, like the animations, I've held off from a rewrite because the whole article needs a rewrite, and I'm busy with some others now. This article is pretty opaque; it seems to have been written by someone who was more interested in showing off his math skills than making a coherent encyclopedia article. The endless math derivations need to be moved to the bottom (and edited down, hidden, or maybe deleted) and some new initial sections written explaining in English how the antenna works. Anyway thanks again for the great discussion. --Chetvorno^TALK 00:48, 14 September 2020 (UTC)

Chetvorno thanks again for the reply. Can we agree on some of the points made in this chat at least so that the facts are somewhere ? I have the time and would be happy to write some text for the article which explains properly voltage and current distribution and exactly why an antenna is resonant and why the impedance at the feed point has no reactance at resonance, subjects which it seems are sadly the cause of confusion everywhere including in some antenna books. Also agreed that often it seems explanations regarding antennas lack any kind of perspective or structure in relation to the technical level of the discussion and in my opinion the complicated mathematics which describes antenna theory doesn't belong in an introduction to dipoles which is what this article is. Agreed also that no one wants to see an exhibition of the technical skills of the authors of Wikipedia articles and the focus in my opinion should be on presenting information in the best way that the most people can understand or similar.

A good explanation would not address a "resonant" dipole (DP impedance resistive) but rather an exactly 1/2 wave dipole. In the latter case, the driving point impedance is 73 j43 ohms regardless of the wire diameter. And again, the emphasis should be on the current, while the voltage pattern is interesting but not very important, especially in the 1/2 wave case where it is highly dependent on the wire diameter EXCEPT at the feedpoint (the only place it matters!) where it is (73 j43)*I.

Also, I'm not sure what you mean by "explanation". The only way of explaining radiation from a dipole is already done concisely in section 5 for the Hertzian dipole. The radiation pattern of longer dipoles can be found by considering a collinear array of Hertzian dipoles (with differing current amplitudes). The easiest way of computing the radiation resistance is through power conservation, as in section 5.1, which is also be done for the half wave dipole in section 2.3 though the math is already becoming quite ugly. The driving point reactance is dealt with in section 6 which is already excessive detail for a wikipedia article in my opinion. And as I said before, any appeal to intuition in explaining any of these will fail. Interferometrist (talk) 14:29, 15 September 2020 (UTC)

@Interferometrist: It would seem to me that it would be more useful to analyze a resonant dipole, rather than one that is exactly 1/2 free space wavelengths long, since dipoles are more often fed at resonance.

The problem we were working on is deriving the current in the dipole; as you said, once one has the current distribution the radiation pattern, total power radiated and radiation resistance can be calculated. Most antenna texts don't bother with this, they simply start from the reasonable assumption that the current and voltage in a dipole are sinusoidal standing waves with a phase difference of 90°. Multiple readers have complained on this page that the standing waves shown in the animations must be in error, since "the current and voltage are not in phase", and the feed voltage is not in phase with the voltage standing wave on the antenna. It's a minor point, but it would be nice to derive the current and voltage by analyzing the dipole as a driven resonator. Can this be done using the Telegrapher's equations, accounting for radiation resistance by assuming the resonator has a distributed resistance of 73 ohms along its length? Or does one also need to solve for the fields? I've never come across a proof that the current and voltage in a dipole are really (approximately) sinusoidal, although it is a reasonable assumption. --Chetvorno^TALK 18:33, 15 September 2020 (UTC)

Again, a 1/2 wave dipole is complicated enough! If you want, you can make it resonant with an external capacitor (etc.), as well as the normal strategy of shortening it slightly. With a 1/2 wave dipole the voltage at the feedpoint indeed IS (as your animation shows) -- almost -- in phase with the current (the current being in the same phase everywhere), but off by about 30 degrees. So no room for complaints, except for the 30 degrees. The problem with illustrating a so-called resonant dipole is that its length, to achieve resonance, depends on the wire diameter. But for illustrative purposes you can certainly draw it, as you did in the animation, which is fine.

More difficult is explaining it, which you can't really do without math and numerical solutions that few (not I!) have actually carried out: solving the Hallen integral equation. But I know the result is this: for thin antennas, a very good approximation for the current is that it falls to zero at the end from the driving current (which we'll take as a given) as cos(kx), all in phase. The voltage along it (and also, "voltage" is not a unique quantity since we are not measuring around a loop! In the derivation used for the Hertzian dipole we adopt the Lorenz gauge) is approx V_1*cos(k(x1-x)) where x1-x is the distance from the end, for a THIN (hi-Q) antenna, which obviously doesn't take into account the effect of the radiation resistance which IS in phase with the current, but DOES explain the change in reactance (phase of that voltage AT the feedpoint) seen when slightly changing the elements' length. So IF you know the voltage at the ends V_1, you can figure out the change in reactance. But that's a big if.....

Because although the standing wave on the antenna resembles, and is physically related to, a standing wave on an unterminated transmission line, you do NOT have a characteristic impedance so the Telegrapher's equation doesn't exactly apply. In order to define a characteristic impedance you'd need the capacitance to be with respect to a conductor much less than a wavelength away. And again, inductance (like voltage) cannot be uniquely defined when there is no closed circuit. What you CAN do is model the entire antenna, as seen by the transmitter looking into it, (but only valid around the resonant frequency) as a series RLC circuit where R is the net radiation loss resistance and LC resonate at f. But what is the L/C impedance level? Again, determined by the wire thickness which enters into the Hallen integral equation. And I understand that the cosine patterns for the voltage and curent I just wrote are only APPROXIMATE solutions which work well for thin antennas but break down when L/d<<100 in which case detailed antenna design becomes purely computational electromagnetics. What I see as useful for Wikipedia, or education in general, is to concentrate on the quantities which have actual solutions, such as the impedance of a 1/2 wave dipole, or the way that the current is split between 2 elements in a folded dipole to quadruple its feedpoint impedance. And then on basic principles such as superposition of Hertzian dipoles, from which the radiation pattern of any wire antenna can be found. And finding the radiation resistance from power conservation. But surely not to try to explain WHY the current and voltage are as they are ALONG a dipole. That problem is extremely complicated (an integral equation, after all!) since the voltage differential (electric field) along the wire affects the current at that point while the divergence of the current (spatial derivative along the wire) determines the build up of charge along the wire affecting the voltage. THAT is the problem you just want to state has a sinusoidal approximate solution, period. Interferometrist (talk) 19:57, 15 September 2020 (UTC)

Well, thinking about it more, I DO see that you might be able to get somewhere viewing the antenna as a transmission line stub, as is used heuristically, but there are no dimensions from which you could determine the delta L and C from first principles. We DO have those effective numbers as could be inferred from the slopes of the curves in the graph which shows the reactance of dipoles of 4 different wire diameters. But again, the connection of wire diameter to that slope is the difficult part. But looking at that graphic I see that I made it myself, so I must have had some idea about it when I did, and I'll have to try to refresh my (leaky) memory ;-) Interferometrist (talk) 20:18, 15 September 2020 (UTC)

Yes, looking at it again and digging up my old code, I see what is known but also the problem. To make that graph I used the induced-EMF method described in section 6.1 to find the input impedance of the dipole given a wire diameter. That works except for the fact that it already ASSUMES the form of the current distribution as being sin(k(x_1 - x)). But that assumption is exactly what is difficult to show, and is only an approximation which becomes poor for larger diameter elements (like most practical antennas needing some frequency bandwidth!). So that's where things stand. Interferometrist (talk) 20:31, 15 September 2020 (UTC)

Interferometrist, thanks for the reply, if the explanation of a half wave dipole is limited to a theoretical ideal half wave dipole them most of the problems you mention disappear. You are making everything sound far too complicated. A dipole which has an impedance of 73 j73 ohms is not a half wave dipole because a half wave dipole by definition is resonant, the length of a real half wave dipole is the electrical length as determined by the velocity of the wave in the material the antenna is made of and not the free space velocity.

Hi, I don't know who wrote that (PLEASE sign your posts using 4 tildes), but I'm finding it a common misconception that the reason a resonant dipole is shorter than 1/2 wavelength is because of a slower speed of light along a wire. There is no such thing (except when surrounded by a dielectric other than free space) and I've removed (all?) such wording from the page which (if you read through enough of it, which I realize might be tedious) gives the correct forms for the current and voltage distributions AND explains why a dipole antenna which is electrically resonant (zero feedpoint reactance) needs to be cut shorter than an actual half-wave dipole.Interferometrist (talk) 14:37, 16 September 2020 (UTC)

@Interferometrist:: Thanks very much for the detailed reply above! That clears it up for me. So a derivation of the currents and voltages is out. I guess I should have realized that since none of the dimensions of the dipole are small with respect to $\lambda$ an equivalent circuit model was inadequate, and full solutions to Maxwell's equations must be used.

I still think that something needs to be said in the article about the heuristic model of the dipole as a linear resonator, to motivate the current and voltage distribution. Even if it doesn't have a characteristic impedance, a thin element dipole seems to function similarly to a driven transmission line resonator (analogous to an acoustic bar resonator). That is how virtually all engineers think of it, and that is how it is intuitively analyzed. The nomenclature used to describe it is that of a resonator: not only equivalent circuit parameters such as resonant frequencies, resistance, reactance, Q factor, bandwidth, etc, but also standing waves of voltage and current, electrical length, phase shift, nodes, loops, harmonics, normal modes, capacitive and inductive loading, etc. The current article uses some of this terminology but does not explain where it comes from. As you say, for a thick dipole this model becomes inaccurate, but it is still widely used and is an important introductory model for newbies. We can simply explain the limitations, in the same terms you used above: for large length/diameter ratios the antenna acts like a transmission line resonator with a continuous "voltage" and "current" along it, but the underlying mathematics is more complicated, and for small length/diameter ratios the circuit model breaks down and numerical electromagnetic simulation programs like NEC have to be used. --Chetvorno^TALK 18:49, 16 September 2020 (UTC)

Well you are absolutely right that the voltage and current distribution along a dipole element closely resembles an open transmission line stub, and acts similarly, and this should certainly be part of the explanation. I was worried about taking this too far since there isn't a characteristic impedance that governs these curves, as there is for coax. Well sorry for the late reply, but I've been looking into this (thus OR, not for placement in Wikipedia!). And I found out I was wrong!

So here is what I found, but DO make any quick checks you can to make sure that I have all my factors of 2 right (or made 2 such mistakes which cancel ;-)

I derived that for a coax stub of characteristic impedance Zo, at around 1/4 (electrical) wavelength long (where it appears as a short) the derivative of reactance per unit length/(electrical) wavelength is 2πZo. From now on consider air core coax. Now I dug up the old software I used to make that graph of the feedpoint impedance for near-half-wave dipoles of various conductor thicknesses, and "measured" the same derivative, for a SINGLE dipole element (1/2 of the dipole feedpoint impedance). The result is the black line in the figure I have posted at: [6]

Also, plotting the same result for coax of 3 different outer radii, I saw that it was the same slope! And in particular, I found (experimentally!) that the dipole element behaves identical to coax with R_outer = λ/2π. So I was wrong: you CAN model (approximately) the current and voltage (not including the effect of radiation resistance) as if it were a transmission line of the same conductor diameter and whose outer radius = λ/2π. I guess it's THAT SIMPLE. And not so simple since I do not have, nor have I ever seen a theoretical justification for this (or even the fact itself). Plus the approximation surely gets worse for larger conductors, where the induced-EMF method breaks down. But I'll be looking out for anyone (RS!) who has already written down what now seems like a rather glaring result.

As far as the article, I agree that any math that doesn't have to be introduced earlier, should be moved towards the end, with the earlier text concentrating on qualitative results or the simplest numerical results only. But it seems that is already the case, largely, with the exception of section 2.1 Short dipole which DOES have a bit of math that might turn away some readers before getting to the next sections. I think it would be best to integrate that math into section 5 Hertzian dipole, perhaps with parallel computations for the short and Hertzian dipoles, having pointed out that the former has an effective current moment (as seen from the far field) 1/2 as large, leading to the 4x difference in the feedpoint impedance and radiated power etc. And keep the main concepts in section 2.1 but not the explicit math, to make it more readable. How's that sound? Interferometrist (talk) 16:40, 21 September 2020 (UTC)

Good Job, Guys. It took a lot of work, but I think the result was worth it. JNRSTANLEY (talk) 12:14, 3 November 2020 (UTC)

Thank Chetvorno, he did all the real work! The rest of us were just here to complain and raise difficult questions ;-) Interferometrist (talk) 22:21, 3 November 2020 (UTC)

If Nothing Changes, Nothing Changes.

JNRSTANLEY, Chetvorno and Interferometrist. I agree, good job guys, the graphic was changed which is better, but apart from that, one year later after all of your good work and all that talking and explanation, nothing else in the article has changed ? :( so far it's all been a waste of time and readers of the article still can't understand how a dipole works in the most basic sense !

It's been clarified that the standing wave on a dipole is stored circulating energy due to resonance, voltage and current are out of phase, the phase difference between V and I of the standing wave does not determine reactance in the feed point impedance, but rather the difference in phase between source voltage and antenna current determines feed point reactance. No one mentioned the idea that the amplitude of the voltage of the source adds vectorily to that presented by the standing wave at the feed points ? The spinning source in the new animation should be replaced by small vertical lines at the feed point ...

How about providing the answers to these questions in the article ?

1. What's the voltage in the graphic, field potential or potential voltage with respect to ground, or something else ? Is it a differential voltage ? Is it a common mode voltage ?

2. Why don't the original traveling waves reflected back from the ends of the dipole go back down the transmission line ?

3. Does the current of the standing wave flow through the source ? Or is it just current on the antenna ? If it's just antenna current, why does it stop at feed points ? Because it gets cancelled out by the opposite polarity and thus cancelling differential current in the transmission line ? Does that work in coax which is unbalanced  ?

4. What determines the feed point impedance ? It's already shown in the equations for R and X that the feed point impedance is determined purely by the frequency of the applied source and the LENGTH and DIAMETER of the elements, the rest of the terms in the equations are constant, but what this really means is that the frequency, length and diameter determine the voltage and current distribution of the standing wave which results when the source of a particular frequency is applied ? Which phase relationships determine feed point reactance ? The equation for feed point impedance is there, it's not that complicated, what's the physical reason that there is reactance > - it was already said, the reason is that the zero crossing point for the (out of phase with source) voltage of the standing wave doesn't line up with the feed points - no one gets this point including all the vastly experienced amateur radio operators in the world ?? They all think the inductive and capacitive reactances cancel at resonance which is completely ridiculous and sad considering that they are the experts and we all look up to them. This idea isn't explained in the article.

5. For a dipole exactly 1/2 wave long, why is the reactance 45 Ω and not zero ? I checked it, it's true as per the equation for impedance, but it doesn't make sense. It should be zero, why is isn't it ?

6. Does the self inductance of wire change the frequency at which resonance occurs ? The waves don't travel slower in metal with no dielectric ? The equations for impedance don't include terms for anything which involves self inductance or velocity factor yet these things affect feed point impedance, does that mean a dipole exactly 1/2 wave long is resonant but at resonance there is 45 ohms reactance ? Is an antenna resonant because it is exactly the right length for the applied source to top up the circulating energy at exactly the right moments ? that means zero reactance doesn't equal resonance ! Is a full wave dipole resonant ? These are all such simple basic questions and no one knows the answers !!!

7. What's the difference between a dipole split in the middle with a source connected to the inner ends of the elements, and that of a dipole not cut in the center so its all one piece but fed with a gamma match ? what's the relationship between standing wave voltage and current and feed point impedance for this set up ?

8. A dipole spit in the center has two elements, each element contributes to feed point impedance, each element has half of R, how do the reactances of each element add together to give the total reactance ? It's not like a loop where everything is in series and it's simple, there is a radiation resistance and then two wires sticking out either side of the feed points, very confusing ?

9. What is the relationship between radiation and the difference in phase between V and I of the standing wave ? Everyone says that the phase difference is not exactly 90 deg but a bit less, and the bit less is caused by radiation ... ? How does reflected V and I from the ends of the antenna not reflect EXACTLY in phase and 180 deg out of phase ? They can't, so then were does the phase change happen ? I don't understand how this works.

Regards, Andrew (Darth), still very confused and sad.

Dear Darth:

1) Please get a username and sign your talk posts.

2) The fact that you could ask all of those questions means that you also should have the ability to think about possible solutions, work out the solutions, and/or research the topic further

3) If you find anything on the page that is actually inaccurate (rather than expressed in a way you don't like or don't understand) then of course call it to others' attention (or fix the mistake yourself, of course)

4) The article is already rather detailed and I don't see any clear holes in it, including after your above rant. Interferometrist (talk) 22:55, 15 August 2021 (UTC)

Darth, thank you for the questions. I understand Interferometrist's viewpoint, but my feeling is that the questions are nevertheless useful for improving the article. Interferometrist, I think Darth may have expected some changes due to my comment above, in which I said more should be written about the dipole as a resonator. Thanks to Interferometrist's work the article is a really excellent mathematical analysis of the dipole, but I feel it is kind of a steep learning curve for an amateur. I think it would help general readers to have some kind of introductory section describing the antenna's operation in nonmathematical terms, with a lot of diagrams. Here's an outline of what it could contain:

A conductive rod acts something like a transmission line. It is resonant at frequencies at which a current wave makes a round trip from one end to the other and back in one cycle, so at lengths of approximately a half wavelength or a multiple of a half wavelength. The dipole is the simplest example of a resonant antenna. The advantage of resonance is that the dipole stores energy in the form of standing waves of current. The phase angle between current & voltage is 90°, so the current nodes are voltage antinodes and vice versa. The ends of the antenna must be nodes. At resonance the stored energy in the standing waves is far higher than the energy input each cycle from the transmitter, so at resonant frequencies the antenna current is far higher. The radio power radiated by an antenna is proportional to the square of the antenna current, so at resonance the dipole radiates far more power than when fed off resonance. A half-wave dipole functions loosely analogously to a tuned circuit: the ends of the rod act as capacitor plates, storing energy in an electric field, while the middle of the rod acts as an inductor, storing energy in a magnetic field. The stored energy oscillates back and forth between the electric and magnetic field. Some of the fields leave the antenna as radio waves, taking energy with them. This makes the rod behave as if it has a distributed resistance, radiation resistance. So near resonance the antenna acts electrically like a lossy tuned circuit.

I have a backlog of unfinished articles I am working through so I haven't had time to work on this, but if no one else does I will take a whack at it in the future. --Chetvorno^TALK 09:25, 5 September 2021 (UTC)

Sure, if you want to write up something like that, then go for it! And integrate it into the current text preferably without excess repetition (some pages have the same thing said over, apparently written by different editors, neither one of whom would appreciate THEIR version being simply deleted so it stays like that!). But here are where I would differ somewhat from what you wrote, in terms of accuracy (and I realize that the intention is simplicity, but simplicity can't be at the expense of accuracy):

A conductive rod [such as a dipole antenna which is SHORTED at its feedpoint] acts something like a transmission line. It is resonant at frequencies at which a current wave ["current" ? Travelling wave, electrical wave, in either case link to transmission line waves] makes a round trip from one end to the other and back in one cycle, so at lengths of approximately a half wavelength or a multiple of a half wavelength. The dipole is the simplest example of a resonant antenna. The advantage of resonance is that the dipole stores energy in the form of standing waves of current. [well I would have said the advantage is that the impedance at the feedpoint is easiest to match] The phase angle between current & voltage is 90°, so the current nodes are voltage antinodes and vice versa. The ends of the antenna must be [current] nodes [since there can be no current beyond the end of the rod] so that if the total length is an odd multiple of lambda/2 there will be a low voltage at the feedpoint which is strongly desired from an impedance matching standpoint]. At resonance the stored energy in the standing waves is far higher [well, not THAT far higher except with an extremely thin - thus hi Q rod] than the energy input each cycle from the transmitter, so at resonant frequencies the antenna current is far higher [not exactly, and it depends on what you kept constant. In practice it really boils down to feedpoint impedance, though you haven't even mentioned the feedpoint yet]. The radio power radiated by an antenna is proportional to the square of the antenna current, so at resonance the dipole radiates far more power than when fed off resonance. A half-wave dipole functions loosely analogously to a tuned circuit: the ends of the rod act as capacitor plates, storing energy in an electric field, while the middle of the rod acts as an inductor, storing energy in a magnetic field. The stored energy oscillates back and forth between the electric and magnetic field. Some of the fields leave the antenna as radio waves, taking energy with them. This makes the rod behave as if it has a distributed resistance, radiation resistance. So near resonance the antenna acts electrically like a lossy tuned circuit.}}

I will finish this later, have to go now Interferometrist (talk) 17:56, 5 September 2021 (UTC)

Re. Darth's question no 5. "For a dipole exactly 1/2 wave long, why is the reactance 45 Ω and not zero ? I checked it, it's true as per the equation for impedance, but it doesn't make sense. It should be zero, why is isn't it ?"

Perhaps we could include a brief answer to this question. There are "end effects" for a physical half wave dipole, which can be visualized as the E fields that extend from the dipole end horizontally out then back around to the other end. These make the electrical length somewhat longer than the physical length and thus if the dipole is cut to a physical half wave it will have a reactive component. Were it possible to suppress these end fields by terminating the dipole in a material with a dielectric constant of zero, this would not happen. Alas, no such material exists.

Another suggestion is that we not say that "Some of the (reactive) fields leave the antenna as radio waves, taking energy with them." Under steady state conditions the driving current fully supplies the energy that converts to the EM wave, independent of the reactive fields. After the drive current goes to zero, the reactive energy sloshing back and forth will continue to maintain the current in the antenna for a time, and THAT CURRENT will keep the EM waves going until it dies out. The fallacy that reactive fields in space convert directly into EM waves is what led to the Cross Field and EM antenna delusions. Many textbook and other animations suggest that reactive waves in space somehow link together to change into an EM wave. This is not so. Only a CURRENT can produce an EM wave.via electron acceleration. These animations would be more accurate if they used a different color or something to show that reactive fields and the E and H fields that are coupled together in an EM wave are NOT the same thing and one cannot change into the other. One can produce the other only if a conductor is present. (such as the dipole) JNRSTANLEY (talk) 21:07, 5 September 2021 (UTC)

I haven't heard that particular explanation of "end effects", that it is due to the shape of the electric field lines near the ends of the dipole. Some textbooks just say it is due to "excess capacitance". If it can be sourced I think that would be a good addition to the article.

On "reactive" vs "radiative" fields, I'm sure you realize there is no physical distinction. There is a single electric field vector and magnetic field vector at each point of space at a given time. In the "reactive field" region, the phase difference between the sinusoidal electric and magnetic field is close to 90°, indicating that most of the energy flow is reactive power which averages zero over a cycle (the reactive energy just flows back and forth between the electric and magnetic field each cycle). As you go further from the antenna the phase difference decreases continuously until far away it approaches zero, indicating all the fields are in the form of electromagnetic waves. My feeling is explaining the near and far field regions, although it should be in the article, is too advanced for an introductory section. Some wording like: "The standing waves store energy in oscillating electric and magnetic fields around the antenna. Some of the fields leave the antenna as radio waves, taking energy with them." is about the level that general readers can comprehend. --Chetvorno^TALK 05:19, 6 September 2021 (UTC)

Thanks for your gracious reply. How about "The standing waves store energy in oscillating electric and magnetic fields around the antenna. Meanwhile, the EM wave, which also has electric and magnetic fields is transporting energy as radio waves which cannot be recovered." We could add (but in the interest of simplicity probably shouldn't here),"Since our measuring instruments which respond to the vector sum of all E or H fields cannot separate the reactive fields from those that are part of the EM wave, pattern measurements must be taken at a point where the reactive waves have fallen to a small value."

Let me add that this distinction arose when I was preparing an IEEE presentation on why "Poynting vector systhesis" on which the Cross field antenna (RIP) was based, doesn't work. That is the reason I am anxious to avoid promoting the idea that reactive fields in space somehow morph into EM waves once their phase somehow gets it right. The nearly out of phase condition you describe results from the vector sum of the two types of E fields, the stronger one being the reactive field and the smaller one the radiative. As the reactive one drops off faster, the NET fields come into phase, but not because the reactive fields are somehow changing their nature and "synthesizing" EM waves. I don't have references at the moment, except for my own work, so I am not interested in including in the article my (perhaps minority) view on this, but I think it valid to avoid stating things ways that promote a misleading view. Sorry forgot to sign JNRSTANLEY (talk) 11:48, 6 September 2021 (UTC)

Actually those equations ARE present in the article, under #Hertzian dipole (which is modified and complicated somewhat for a longer dipole, but that just comes from a superposition of such current elements). But while they give the fields properly, (agreeing with Chetvorno) I do not think there is any validity in talking about the radiating versus reactive component of the electric field, or of the magnetic field. Rather you need to talk about the Poynting vector, and the real part of the Poynting vector (for a Hertzian dipole) is always radial and falls off as r^-2, whereas the imaginary part is what has components in the theta direction as well as the r direction, and which quickly falls to zero as r increases beyond the nearfield (well I guess you could say the E_r component is always reactive inasmuch as it never contributes to S_r, but you couldn't possibly know that without knowing the direction of H). However I will rather propose wording focusing on the element current rather than the fields, for which the current wording I believe is good.

Also, the description of stored energy would be good for talking about an LC circuit, but a halfwave dipole antennas has a rather low Q and in fact the radiated power has only to do with the current actually flowing regardless of resonance. I will propose some wording to that effect which perhaps one of you can integrate into the article. Also, I'm not sure that "end effects" {CN} can account for the 43 ohm reactance, nor that we need to explain that further than it already is (with two graphs and a reference to the induced EMF method). Interferometrist (talk) 01:09, 8 September 2021 (UTC)

Proposed text (draft)

A conductive rod (such as a dipole with its feedpoint shorted) acts something like a transmission line, with electrical waves traveling in both directions. Like a transmission line stub, the electrical wave is reflected from each end (the currents due to the incident and reflected wave there must add to zero) and the net result is a standing wave with a current node at each end. If the length of the antenna is an odd multiple of λ/2, then there will be a voltage node at the center, which is where the feedpoint is (usually) placed. For traveling waves of ÷a given current I_0, that allows the feedpoint to have a relatively low voltage, whereas at any other position (or at the center of any other length dipole) the voltage would be much higher.

This is a great advantage in connecting the antenna to a transmitter or receiver, since the terminal impedance is equal to that voltage across the feedpoint divided by the current I_0. When the feedpoint is shorted, an incoming radio wave can induce a current in the antenna (in the form of such a standing wave) which will promptly be re-radiated. If the external circuit induces a voltage at the feedpoint in phase with the external current, then power will be added to the standing wave (from a transmitter). If the feedpoint voltage is of opposite phase from that current, then power will be drawn away from the standing wave (to feed a receiver). In all cases, a radio wave will be produced solely in proportion to the current I_0 in the conductor (see #Hertzian dipole), but in the latter case (a receiving antenna) that wave will be in a phase that removes power from the EM field.

In addition to the current through the antenna element, one can speak of the electric field at the antenna element. However the magnitude of that electric field can be large or small but has essentially no effect on the coupling of the antenna to the external EM field. The magnitude of those electric fields depend greatly on the diameter of the conducting rod. The amount of charge that is deposited, for instance, near the ends of the rod during each cycle, is dependent only on I_0 (and the frequency). For a rather thick rod, that charge will be distributed over the conductor's circumfrance and produce a rather small electric field. For a very thin rod/wire, the charge will be much more concentrated, resulting in a large electric field. That also means that the stored energy in the antenna is that much larger, resulting in a much higher Q (and consequently narrower bandwidth of the resonance). But the advantage of cutting the antenna length to a half wave, is that at the feedpoint the voltage will be quite small, regardless, resulting in a feedpoint impedance of 73 j43 Ω (the residual 43 ohms of reactance can be eliminated with a slight length adjustment, as detailed above).

How does that sound? Interferometrist (talk) 01:58, 8 September 2021 (UTC)

Interferometrist, your last paragraph states some important things very well. The diameter of the dipole does indeed determine the Q, (ratio of stored to radiated energy) as well as the amount of end effects, with more shortening needed for fatter dipoles. As to how the 43 ohms inductive appears, consider that excess capacity at the "hot" end, will transform to added inductance at the fed end, one quarter wave away. I am OK with no additional discussion of end effects for now. I have found a number of sources, the best two probably, http://on5au.be/Cebik-2/CalibratingKToNec.pdf which references S. A. Schelkunoff, Electromagnetic Waves (New York: Van Nostrand, 1943), p. 465 the latter of which I don't have access to. I am presently writing up a document that uses a FEA simulation to quantify the effect of the capacitive fringing fields off the ends of a typical dipole, and if and when it is published, we can perhaps pursue this further. JNRSTANLEY (talk) 11:50, 8 September 2021 (UTC)

Reactions, off the top of my head:

@Interferometrist: I definitely agree that my version needs more about impedance. But I think general readers, and even many radio hobbyists, do not understand the relation of resistance, reactance and impedance. In my draft above, I was hoping to start it off by answering two important questions before introducing technical terms like impedance, in a way that almost all readers could understand:

• Why is the dipole the most important and widely used antenna?

Because it is the simplest resonant antenna

• Why is it driven at resonant frequencies? Why is resonance important?

Because at resonance the antenna stores energy as standing waves. Therefore the antenna current is higher at resonance, therefore the radiated power is higher.

A more complete explanation, that the higher current at resonance is due to minimum impedance due to zero reactance, or no reflected power, could go later in the section.

I like the heuristic explanation of the lower Q of a thick dipole as due to difference in the electric fields. But I'm wondering if that level of detail needs to be in an elementary how-it-works section? Maybe it could go further down in the article. I am rewriting Monopole antenna (see the draft at User:Chetvorno/work6) and it seems to be clearer to explain details like end effects and bandwidth in separate sections (any criticism or advice on the draft would be welcome!) --Chetvorno^TALK 22:20, 10 September 2021 (UTC)

@JNRSTANLEY: your point that the inductive reactance of a half wave dipole element is due to end capacitance transformed by the $\lambda /4$ section sounds great! Again, I'm wondering if that technical detail should be in an introductory explanation, or further down in the article. --Chetvorno^TALK 22:20, 10 September 2021 (UTC)

@Chetvorno:Thanks for your additional constructive comments. I am fine with putting the items you mentioned later in the article. My one question about your proposed text relates to this: Because at resonance the antenna stores energy as standing waves. Therefore the antenna current is higher at resonance, therefore the radiated power is higher.

This could be taken to mean that a higher Q dipole would radiate more than a lower Q one The radiated power will be the same as the input power (less losses) independent of the stored energy. But as you next point makes clear, getting the power into the dipole is easier when it is resonant.

JNRSTANLEY (talk) 11:08, 11 September 2021 (UTC)

@JNRSTANLEY: @Chetvorno: Yes, that's exactly the problem. It is wrong to say that the resonance of the antenna has to do with it radiating well. A .5 wave and .4 wave dipole driven with the same feedpoint current have almost exactly the same radiation pattern and total radiated power, because it is only the current elements integrated that result in the radiating field. The voltage present has a lot to do with GETTING that current into it, but not on the radiated power (the dual, a 1/2 wave slot antenna, likewise radiates according to the VOLTAGE across the slot regardless of the current needed to achieve that voltage).

I understand the desire to make it simple enough to understand to a wider audience, and that's good as long as it's accurate. You don't have to use the word impedance, but anyone who understands what both voltage and current mean already has at least an intuitive idea of impedance, which is what I was getting at when I wrote ".... a given current I_0, that allows the feedpoint to have a relatively low voltage ...... is a great advantage in connecting the antenna to a transmitter or receiver...." -- whether you use the word impedance or not. Because, after all, it is ONLY the terminal impedance that changes remarkably at resonance. Thus the same antenna, but with very different conductor diameters ALL radiate similarly at resonance, even though one has a much higher Q than the other. The greater stored energy in the thin antenna doesn't help it radiate any better at all, and if both are 1/2 wave you can't even tell the difference without looking at it. If anything, the LESS resonant (fat conductor) antenna is preferable (regarding performance) because it has a wider operating bandwidth. But if you MUST use a thin conductor (like if it's 100 meters long strung between two poles) then you want it resonant so you can radiate 100w with less than 100v, not the kilovolts you'd need if it were 5% shorter. Again that has to do with impedance, whether you use the word or not (and moreover with impedance being largely reactive in that case, a further issue not needing to be detailed in the simple explanation). So for explanatory purposes, I would suggest text like that, saying that you can get the same power with a much lower voltage, and THEN say "impedance" even if that word goes over some readers' heads.

Now I'm interested in the explanation of the shift in the electrical resonance being due to "end effects" but am a bit skeptical, or at least would want to see it quantified. Yes, I understand very well how a capacitive impedance at the end of the antenna can transform to an inductive impedance at the feedpoint, as with a transmission line, but that doesn't quite explain the quantitative results. In particular, I would ask how it is that dipoles cut to exactly 1/2 wave but of different diameters (and different Q's) ALL have exactly the same 43Ω reactance (and 73 ohm resistance) driving point impedance. If the 43j ohms is from an end effect, how is that computed (and the same for conductor diameter) with 1/2 wave, and then very different with respect to conductor size at a different length? I don't think this is an easy problem (in fact it requires numerical solution) and just calling it an "end effect" doesn't help unless those words point you to a solution that gives you quantitatively valid results. And what about, for instance, a resonant loop antenna? It doesn't even have ends. Interferometrist (talk) 22:00, 24 September 2021

@Interferometrist: I hadn't remembered that ALL dipoles have 43 ohms reactance when cut to a physical half wave, even though it is indicated in one of the graphics already included, and I have verified it within the accuracy of the NEC simulation. If we make the dipole fatter, two things happen. The end capacity is increased, but also the Zo of the wire acting as a transmission line is lower. This possibly is what brings the reactive part back towards 43 ohms. At least this is my guess as to HOW this happens. It seems obvious that a fatter dipole will have more capacity in the fringing fields, and yet somehow this does not change the 43 ohms figure.

If the fat dipole has greater bandwidth, as we seem to agree, then a fatter dipole will have to be shortened more to get to resonance, as NEC also confirms, since the reactive part will change more slowly than with a thin dipole. This was known in 1952 empirically as curves were published (1952 ARRL handbook)to show the value of shortening due to "end effects" (This is already well covered in the section "Impedance of dipoles of various lengths") The 1952 ARRL value for a thin dipole is 2% and for an L/d ratio of 10 (fat dipole)it is shown as 8%. (NEC shows the same trend, but with even larger differences). The empirical values likely included the effect of end insulators for the thin dipoles, but not the fat ones.

If we ONLY add capacitance to the ends of a physical half wave, (called a "top hat" when done with vertical monopoles), the inductive reactance at the feed point changes. In this case only the end capacity changes but the wire (mast) Zo does not. I imagine these things can be confirmed with other types of analysis other than NEC, and no doubt has been done, but I am not one who can do that. All of this is important in the design of conical dipoles which have very wide bandwidth. Strongly tapered AM towers that are fat at the bottom show the opposite effect, that is, they have to be more than a physical half wave to resonate. Perhaps including a mention of the change in the resonant length with tapered dipoles is worthwhile. NEC users with tapered aluminium yagi elements are well aware of this necessary correction factor. JNRSTANLEY (talk) 12:32, 25 September 2021 (UTC)

DAB - digital radio.

There is no information specifically relating to DAB. — Preceding unsigned comment added by 84.93.82.80 (talk) 20:23, 7 October 2016 (UTC)

Same kind of antennas work for DAB, just have to be suitable for the frequency. The bandwidth of DAB is not cause for concern. Graeme Bartlett (talk) 10:33, 16 August 2021 (UTC)

External links modified

Hello fellow Wikipedians,

I have just modified one external link on Dipole antenna. Please take a moment to review my edit. If you have any questions, or need the bot to ignore the links, or the page altogether, please visit this simple FaQ for additional information. I made the following changes:

• Added archive https://web.archive.org/web/20111222223519/http://www.aroesner.homepage.t-online.de/balun.html to http://www.aroesner.homepage.t-online.de/balun.html

When you have finished reviewing my changes, you may follow the instructions on the template below to fix any issues with the URLs.

This message was posted before February 2018. After February 2018, "External links modified" talk page sections are no longer generated or monitored by InternetArchiveBot. No special action is required regarding these talk page notices, other than regular verification using the archive tool instructions below. Editors have permission to delete these "External links modified" talk page sections if they want to de-clutter talk pages, but see the RfC before doing mass systematic removals. This message is updated dynamically through the template {{source check}} (last update: 5 June 2024).

• If you have discovered URLs which were erroneously considered dead by the bot, you can report them with this tool.
• If you found an error with any archives or the URLs themselves, you can fix them with this tool.

Cheers.—InternetArchiveBot (Report bug) 03:07, 11 September 2017 (UTC)

The adjustment factor k is equivalent to v/c.

I've marked the sentence in the main article, topic heading above, as needing some verification the mildest way Wikipedia allows. The goal of compensating for the feedpoint inductance with antenna shortening has everything to do with maneuvering overall reactance of the antenna elements, not the velocity of propagation of the wire. I'd love to be proven wrong. If someone can provide a good reference from a college text book or engineering paper backing up the claim k = v/c, please do so. crcwiki (talk) 20:15, 30 October 2017 (UTC)

@Crcwiki: Yes you are absolutely right: the wire itself propagates signals at the speed of light, period. With the end reflecting the signal and the wire radiating some of its energy, you get a voltage & current pattern from which this isn't clear, but that confusion is not a property of the wire. The only reason I haven't changed it is that I was overruled when I attempted to, though this was on the Antenna page (but I think I remember it happened on this page too) see Talk:Antenna (radio)/Archive 1#Invalid reference to "velocity factor" . But you are right, v<c is just wrong and should be fixed. Interferometrist (talk) 16:13, 4 June 2018 (UTC)

External links modified

Hello fellow Wikipedians,

I have just modified 3 external links on Dipole antenna. Please take a moment to review my edit. If you have any questions, or need the bot to ignore the links, or the page altogether, please visit this simple FaQ for additional information. I made the following changes:

• Added archive https://web.archive.org/web/20070508221040/http://www.ycars.org/EFRA/Module C/AntDip.htm to http://www.ycars.org/EFRA/Module C/AntDip.htm
• Added archive https://web.archive.org/web/20060907074441/http://stewks.ece.stevens-tech.edu/sktpersonal.dir/sktwireless/lin-ant.pdf to http://stewks.ece.stevens-tech.edu/sktpersonal.dir/sktwireless/lin-ant.pdf
• Added archive https://web.archive.org/web/20070926195106/http://www.nt.hs-bremen.de/peik/asc/asc_antenna_slides.pdf to http://www.nt.hs-bremen.de/peik/asc/asc_antenna_slides.pdf

When you have finished reviewing my changes, you may follow the instructions on the template below to fix any issues with the URLs.

This message was posted before February 2018. After February 2018, "External links modified" talk page sections are no longer generated or monitored by InternetArchiveBot. No special action is required regarding these talk page notices, other than regular verification using the archive tool instructions below. Editors have permission to delete these "External links modified" talk page sections if they want to de-clutter talk pages, but see the RfC before doing mass systematic removals. This message is updated dynamically through the template {{source check}} (last update: 5 June 2024).

• If you have discovered URLs which were erroneously considered dead by the bot, you can report them with this tool.
• If you found an error with any archives or the URLs themselves, you can fix them with this tool.

Cheers.—InternetArchiveBot (Report bug) 12:08, 11 December 2017 (UTC)

Recent changes to animated diagram caption

I'm concerned about the recent wording changes User:87.254.86.39 made to the caption of the dipole antenna animation. Since this animation is virtually the only nontechnical explanation of how a dipole works in this very technical article, this caption is important for general readers.
The original caption read:

A half-wave dipole antenna receiving power from a radio wave. The electric field of the wave (E, green arrows) pushes the free electrons in the antenna elements back and forth (black arrows), charging the ends of the antenna alternately positive and negative. Since the antenna is a half-wavelength long at the radio wave's frequency, it excites standing waves of voltage (V, red bands) and current in the antenna. These oscillating currents flow down the transmission line through the radio receiver (represented by the resistor R). The action is shown slowed down in this animation.

The new caption reads:

A metal half-wave dipole antenna receiving power from a radio wave at that wavelength, in slow motion. The electric field of the radio wave (  E, →) acts on the free electrons in the antenna forming a current (  →, magnitude exaggerated). As this is a half-wavelength antenna, the voltage it excites form standing waves (  V, bands). Oscillating currents then flow across the poles of the antenna; here, connected to a resistor, R, but generally to a radio receiver.

I think the original wording was better and should be restored. My objections are:

• "The electric field...acts on the free electrons in the antenna forming a current (magnitude exaggerated)." :

How does it act on them? The previous wording clarified this for nontechnical readers; it exerts force on them, "pushes [them] back and forth". Also, what does "magnitude exaggerated" mean? That the currents in the drawing are shown with too large a magnitude? How? They are just arrows in a drawing; no magnitude is specified.

• The new text references to color-coded parts of the drawing are much more cryptic than the previous format: Referring to the electric field arrows, (E, green arrows) was clearer than (  E, →)
  (V, red bands) was clearer than (  V, bands). These violate MOS:COLOR; color alone should not be used to distinguish parts of text.
• "Oscillating currents then flow across the poles of the antenna...".

The point where the antenna connects to the transmission line is called the "feed point", not the "poles". It is important to introduce correct terminology so that general readers can understand the rest of the article.

• "...connected to a resistor, R, but generally to a radio receiver."

As the original text made clear, the resistor represents the radio receiver.

• "A metal half-wave dipole antenna receiving power from a radio wave at that wavelength..."

What wavelength? This is not as clear as the previous wording "...the antenna is a half-wavelength long at the radio wave's frequency...".

• "As this is a half-wavelength antenna, the voltage it excites form standing waves..."

Besides the awkward syntax and grammatical mistakes, it is important to make clear that both the voltage and current form standing waves.

--Chetvorno^TALK 07:28, 31 January 2018 (UTC)

I think all of the above cited technical objections are valid. I will also take the style objection as valid and revert to the earlier version (before I edit further).

Also (applying to both versions) it is not really correct to say that the current ("electrons are pushed") is due to the electric field of a received wave. If there were only an electric field then it would not lead to a large current (even considering a shorted feedpoint) as the field gets reduced near the metal. But for an EM wave the curl of the propagating magnetic field (minus the current already created in the conductor) creates an E field inside the conductor regardless, which is responsible for creating that opposing current. For a 3/2 wave dipole the current in the outer limbs is opposite the one on the inner portion. We should avoid oversimplification.

Understanding an antenna receiving a wave from a particular direction is difficult. The figure shows only the incident wave but ignores the E field (let alone H) reradiated by the antenna. A better approach is to analyze a transmitting antenna and then appeal to reciprocity.

And yes, no one talks about "poles" in an antenna. Such wording is not acceptable, and editors DO need to "engage". Interferometrist (talk) 23:12, 31 January 2018 (UTC)

Section: Dipole antennas of various lengths

I challenge the notion the longer antennas described in the "Dipole antennas of various lengths" section of the main article meet the definition of dipole antenna according to the IEEE-100-1984 and ANSI/EIA/TIA-329-B-1999. According to the definition a dipole antenna has no more than two current nodes. This rules out longer antennas with three or more current nodes that are more like long-wire than discrete dipole antennas.crcwiki (talk) 20:27, 1 March 2018 (UTC)

I am not familiar with ANSI / EIA / TIA-329-B-1999. I have owned a copy of the IEEE standard dictionary (I don't recall which edition I had). The IEEE standards dictionary just copied definitions from various IEEE standards, out of context. Definitions that made sense in the context of a particular standard do not make sense outside of that context. I found the dictionary so unreliable that I threw it away. Jc3s5h (talk) 20:43, 1 March 2018 (UTC)

Yes I noticed IEEE-100-1984 is a compendium of definitions from other documents as well. The dipole definition comes from a predecessor of IEEE-145-1993 (that I have in front of me) that states the same definition as seen in another talk section above. IEEE-100 and now also IEEE-145 are currently our only primary references to the definition of a dipole from none other than the IEEE. The key part of the definition is "Any one of a class of antennas producing a radiation pattern approximating that of an elementary electric dipole." Any definition of a dipole that includes more than two current nodes violates this. If you have a primary reference that carries more weight than a standard from an organization catering precisely to work in electromagnetics, let's see them.crcwiki (talk) 21:26, 1 March 2018 (UTC)

Yeah, that definition doesn't seem to be consistent with usage in most of the literature. The antenna textbooks I've looked at include dipole antennas with more than 2 nodes; the 3/2 wave dipole, the 5/2 wave dipole, etc. [7], [8], [9], [10], although some technology encyclopedias seem to restrict the def to the half-wave dipole [11]. --Chetvorno^TALK 04:51, 1 April 2018 (UTC)

I see the same as you in some of the literature. Most annoying is the text books rarely get around to actually defining what a dipole is. It's as if it is assumed. All that said, that IEEE definition just didn't come out of thin air. The contributors to IEEE-145 are likely antenna nerds from industry, research and universities. For them to come together on something like this definition of a dipole says a lot and carries some weight.crcwiki (talk) 15:08, 11 September 2018 (UTC)

I took that qualification out of the "definition." It is clearly wrong, whoever came up with it. Also wrong (marked CN) is saying that its radiation pattern must be similar to a short dipole. Maybe unqualified "dipole" doesn't have a concise definition. Interferometrist (talk) 18:44, 3 June 2018 (UTC)

Actually I see now I shouldn't have marked it CN since that there IS a citation. I'll invite someone else to deal with it. No definition is better than an incorrect one IMO. Interferometrist (talk) 18:48, 3 June 2018 (UTC)

Now I've reconsidered the objection to the portion of the "definition" about only 2 nodes. Indeed the resonant portion of the current that dominates the current along the antenna (especially if hi Q) is a standing wave in quadrature with the voltage pattern and crosses zero where the voltage is at a maximum (including at the ends). But that ignores the smaller out of phase (thus in phase with the voltage) component that is NOT zero at an intermediate node, so not technically a node. It occurred to me, that if there were really no current at some point along the element, then it wouldn't be possible for power to be electrically transferred to (and then radiated from) the outer portion of the element (just as the voltage doesn't go to zero at the feedpoint, just the component of voltage in quadrature with the current). Which doesn't completely settle the matter since it could be that the outer segment of the element doesn't radiate net power, just resonates (receiving power from the field), but I don't think that's the case. (Though I still wonder why this fine point is an important defining quality of the dipole.) So sorry, I edited without really being sure of what I was saying or thinking it through. Interferometrist (talk) 14:40, 4 June 2018 (UTC)

I will remove the citation needed then.crcwiki (talk) 15:08, 11 September 2018 (UTC)

Introduction: "monopole antenna" is a misnomer?

I am concerned about these sentences recently added to the introduction:

"However "monopole" is somewhat of a misnomer since the source exciting far-field radiation can only be an oscillating electric dipole (or magnetic dipole), never a higher multipole order (quadrupole, octupole, etc.) nor a monopole (isolated positive or negative charge). The feedline injects an equal and opposite current into the ground (or ground plane) as it supplies to the radiating element, resulting in fields and currents at and above ground of the same form as for a dipole with two such elements opposite each other."

I wouldn't mind this issue noted briefly in the body of the article, but it shouldn't be in the introduction, this technical digression will just confuse general readers (WP:EXPLAINLEAD, MOS:JARGON, WP:SURPRISE). It is unnecessary; any reader who knows what monopole, dipole, and quadrupole radiation is already knows that EM waves are dipole radiation and how a monopole antenna works. I particularly object to calling the term "monopole antenna" a "misnomer"; the adjective "monopole" modifies "antenna", and simply refers to its single driven element. No antenna text that I can find calls it a "misnomer". The single supporting citation given (Pfaff) does not support it. The Pfaff source is not calling all monopole antennas a misnomer, it is specifically referring to a monopole antenna on a spacecraft. It is saying that the body of the spacecraft is too small to act as an adequate ground plane, so "...the spacecraft body effectively acts as the second element of a dipole", it acts as a radiator, its potential oscillating 180° out of phase with the monopole element. Obviously does not apply to monopoles with adequately sized ground planes. --Chetvorno^TALK 03:16, 1 April 2018 (UTC)

Well I'm sorry anyone wasted their time with this as clearly there is (probably) no citation. And so yes, it can be removed. I was the one who inserted it but never said there was a RS (someone else added the erroneous ref), just that it's clearly so......

the adjective "monopole" modifies "antenna", and simply refers to its single driven element.

Yes that's why the misnomer works, but that's also why it's problematic. Do you call a turnstile antenna a quadrapole? No, of course it's a pair of dipoles (unless you fed it very wrong!). A similar 3-phase antenna isn't called a tripole, its effectively 3 dipoles, in terms of how it radiates. So a monopole is a dipole too. Interferometrist (talk) 02:18, 4 June 2018 (UTC)

I see your point, but different names are needed to distinguish these two important classes of antenna, and "monopole" and "dipole" are at least visually evocative. It's probably too much to expect that all scientific names can be made completely consistent (I'm still wondering how the two words "flammable" and "inflammable" came to be used for the same property :D) --Chetvorno^TALK 20:55, 5 June 2018 (UTC)

Gain calculation of a half-wave dipole is wrong

The calculation of gain is given as 4/Cin(2 Pi) = 1.64 = 2.15 dBi, where Cin is the cosine integral.

However, when I compute that in Mathematica, I obtain 4 / CosIntegral [ 2.0 * Pi] = -177.3, rather than 1.64. An online calculator for the cosine integral at https://keisan.casio.com/exec/system/1180573424 shows the cosine integral of 2 Pi to be -0.02256066, so 4/-0.02256066 is -177.3, which confirms the Mathematica result. As such, I conclude the Wikipedia calculation is incorrect. Drkirkby (talk) 13:52, 26 December 2019 (UTC)

It seems that there are two different but related functions called the cosine integral. The relationship is

$\mathrm {Cin} (x)=\gamma \ln(x)-\mathrm {Ci} (x)$

where $\gamma =0.577216$ is the Euler–Mascheroni constant. The aforementioned online calculator gives

$\mathrm {Ci} (2\pi )=-0.0225607$

and so

${\begin{aligned}\mathrm {Cin} (2\pi )&=\gamma \ln(2\pi )-\mathrm {Ci} (2\pi )\\&=0.577216 1.83788 0.0225607\\&=2.43765\end{aligned}}$

and

${\frac {4}{\mathrm {Cin} (2\pi )}}=1.64092$

which is 2.15088 dBi catslash (talk) 03:20, 27 December 2019 (UTC)

Yes, you are correct. I have put a note in the article to say that they should not be confused Drkirkby (talk) 10:49, 28 December 2019 (UTC)

The term "directive gain" is repeatidly used, when directivity should be used instead

The article makes repeated use to the term "directive gain" which is a term I see rarely used elsewhere. The 1983 edition of the "Use of Standard Definitions of Terms for Antennas & Propagation": IEEE Std. 145 says:

"A substantive change included in this revision is the deprecation of the term directive gain and its replacement by the term directivity. This change brings this standard in line with common usage among antenna engineers and with other international standards, notably those of the International Electrotechnical Commission (IEC)."

Given the term "directive gain" was depreciated 36 years ago, it makes sense to use directivity instead of directive gain. The latest edition of the IEEE standard just says "directive gain: [Deprecated.] See: directivity." Drkirkby (talk) 11:03, 28 December 2019 (UTC)

Hertzian dipole time dependence

This is kind of minor but Hertzian dipole should either have $e^{-i\omega t}$ or $e^{j\omega t}$ dependence by convention; $e^{-ikr}/{r}$ in the dipole field formula (which comes from the Green function) indicates a converging (not diverging from the source) spherical wave as well. Classical Electrodynamics uses $e^{-i\omega t}$ dependence as well, while Microwave Antenna Theory and Design, which the section cites, uses $e^{j\omega t}$. -Myxomatosis57 (talk) 21:27, 13 February 2020 (UTC)

Two botched edits in a row.

I changed the chart to say "Resistive and reactive" rather than "Real and imaginary" and tried to make the comment "'j' is imaginary but reactive impedance is very real." Twice in a row the edit Published before I was ready. I don't know why, but I'm using a (rather clumsy) tablet and must have slurred a key - but I'm pretty sure I didn't hit the Enter button. Nor did I get a final look at what I was about to submit. Could someone who knows how please submit this comment to the appropriate area, with the request "Please add more confirmation before a mobile device Publishes an edit". And I have previously had the comment (not quite as bluntly put): "Mobile devices are crap; why are you using one". No, I think it should be possible to use a mobile device to make a minor edit and have it work the way you would expect. 203.220.159.238 (talk) 10:44, 8 October 2022 (UTC)

Mobile devices are intended only for displaying advertising; you'd be better off using a Morse key for editing. --Wtshymanski (talk) 04:05, 17 October 2022 (UTC)