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Hi - if there's anyone out there. I've created some 3D far field plots ( Image:Radiation-patterns-v.png), and intend to put them on this page. In order to have enough text to go with both the existing and new images, I reckon I'll add some words defining cuts (great-circle and maybe conical cuts) through the pattern. Stop me now if you don't agree! -- catslash 00:25, 1 August 2006 (UTC)
...but instead I added a section on reciprocity of antenna patterns, as this seemed a major omission. I was going to put this on the reciprocity theorem page, but that article is already long enough, and too nice for me to mess with. But- should this article be called antenna pattern (which currently redirects to this one)? -- catslash 22:15, 30 August 2006 (UTC)
Since you are taking the Lorentz reciprocity theorem as a given, I don't understand why the proof that an antenna works equally well as a transmitter and receiver, for the same radiation pattern, needs to be so long. It seems like you can prove it in a few lines:
Note that this proof is equally true in the near and far field, in inhomogeneous materials (e.g. if the antenna is placed inside a waveguide, as an extreme example), and tells you that the polarization sensitivity of the antenna is reciprocal and not just the angular pattern. Hence, it is both simpler and more general than the argument that currently appears in the article. Moreover, the argument currently in the article says that "reciprocity requires that the power transfer is equally effective in each direction," which isn't a very precise statement of the reciprocity theorem.
Am I missing something?
—Steven G. Johnson 01:50, 3 September 2006 (UTC)
You wrote: Re. Circuitous; Sorry that wasn't a fair description. I meant do we need to go from the reciprocity theorem stated in terms of spatial integrals, down to a result for a single point, then (via our knowledge of the possible modes), to the amplitude of the signal (which is an integral over the feed cross-section). I suspect there must be a more direct way, because this method breaks down once we consider more than a handful of modes (because there will be no suitable point).
Yes, I do think you need to start from the reciprocity theorem stated precisely (i.e. as integrals of the fields/currents). The essential fact is this: you have to define what you mean by the "power" in a "channel", and in particular relate it to the fields. For a single mode, the power can be defined in terms of the field at any single point, so this is easy. For multiple modes/channels, you have to be able to decompose them somehow, which you normally do by orthogonality—that is, instead of using the field at a single point, you use an integral of the field against a mode pattern, or a current with the same pattern as the mode, so that you only couple to a single mode.
I would say that the theorem about the "radiation pattern" being reciprocal implicitly assumes a single operating mode in order for the "radiation pattern" to be uniquely defined. (There can be other modes, of course, but you can only use a single superposition of them in this simple version of the theorem.) As soon as you get to the more general multi-mode case you are really talking about the S-matrix, which should go into a separate article. My inclination would be to prove only the single-mode case in this article using the simple single-point argument, and refer to the (still to-be-written) S-matrix article for the multi-mode situation. (Or you can just prove the general S-matrix case on its page, and refer to reciprocity here as a special case. However, the single-mode case follows so simply from Lorentz reciprocity that I think it is probably worthwhile to prove it separately for pedagogical reasons.)
—Steven G. Johnson 21:13, 4 September 2006 (UTC)
I'm going to replace the article lead (?), to emphasize the distinction between the far-field pattern and the near-field pattern, and to reflect the fact that radiation pattern can mean either (I'll also make this distinction in the reciprocity section). Here's what I'm snipping out..
-- catslash 13:25, 7 September 2006 (UTC)
Thanks for the vote of approval - you'd better write a page on integrated optics now! There's still a lot to do on this page of course. -- catslash 14:46, 8 September 2006 (UTC)
I don't get the logic in the end of the proof: "Analysis of a particular antenna (such as a Hertzian dipole), shows that this constant is , where λ is the free-space wavelength. Hence, for any antenna". It seems to me like a generalization to the general from the particular that is not obvious. —Preceding unsigned comment added by 80.216.130.104 ( talk) 10:11, 7 March 2009 (UTC)
One question I always had on antenna gain plotting is the difference between rotating the antenna (with signal source attached) and recording the signal strength from a fixed location (same as walking around a fixed antenna with a receiver, taking the path of a constant radius circle and recording received signal strength), and walking around with a receiver and following the path of constant received amplitude. The latter is what you would see if the transmitted energy was visible, the true shape of the field in space. The former collects data about signal strength and therefore antenna gain at different angles, but if you plot it on linear or log scale, you don't get the real world spacial distribution of the energy. If you superimposed an antenna pattern on a map, and assumed that people (with a receiver of a certain threshold) could receive the signal if they were inside the pattern, it would be the latter pattern only that would work, not the standard log gain plot. In ideal space, the "walk around" iso-amplitude pattern would follow 1/r^2 rule after the antenna gain were applied in each direction. Another issue here is if, in the walk around process, you had an antenna null that caused you to travel into the near field area of the antenna, some strange things would happen. You would have to use enough power into the antenna so that your receiver would work everywhere outside the near field while walking the constant signal strength path.
I wish this Wikipedia article addressed these not so obvious issues with measuring and plotting radiation patterns. I personally don't feel qualified to do this. 192.80.95.243 ( talk) 16:33, 28 December 2010 (UTC)
Someone remarked the proof of this is long, but I don't see why such a proof is needed. That's a completely separate topic. You wont find the proof of the reciprocity theorem in any antenna book in a section devoted to the radiation pattern.
It just strikes me someone knows a proof of it, so they thought they would write it in the section on radiation pattern. IMHO, the reciprocity theorm should just be reffered to, and a link to it on another Wikipedia page. It is unneeded in a section on radiation pattern. Sure, it is helpful to know about it for antenna analysis, but so are dB too, and its useful to know what a transmitter is. Is there a need to explain all them?
IMHO, the whole section should be removed. Drkirkby ( talk) 23:15, 15 April 2012 (UTC)
The figure showing a rectangular radiation plot is mislabeled as showing directivity in dBi. It is actually showing a normalized power pattern in dB relative to peak, because a 0 dBi antenna can only be an isotropic radiator.
This is the
talk page for discussing improvements to the
Radiation pattern article. This is not a forum for general discussion of the article's subject. |
Article policies
|
Find sources: Google ( books · news · scholar · free images · WP refs) · FENS · JSTOR · TWL |
![]() | This article is rated Start-class on Wikipedia's
content assessment scale. It is of interest to the following WikiProjects: | ||||||||||||||||||||||||||||||
|
Hi - if there's anyone out there. I've created some 3D far field plots ( Image:Radiation-patterns-v.png), and intend to put them on this page. In order to have enough text to go with both the existing and new images, I reckon I'll add some words defining cuts (great-circle and maybe conical cuts) through the pattern. Stop me now if you don't agree! -- catslash 00:25, 1 August 2006 (UTC)
...but instead I added a section on reciprocity of antenna patterns, as this seemed a major omission. I was going to put this on the reciprocity theorem page, but that article is already long enough, and too nice for me to mess with. But- should this article be called antenna pattern (which currently redirects to this one)? -- catslash 22:15, 30 August 2006 (UTC)
Since you are taking the Lorentz reciprocity theorem as a given, I don't understand why the proof that an antenna works equally well as a transmitter and receiver, for the same radiation pattern, needs to be so long. It seems like you can prove it in a few lines:
Note that this proof is equally true in the near and far field, in inhomogeneous materials (e.g. if the antenna is placed inside a waveguide, as an extreme example), and tells you that the polarization sensitivity of the antenna is reciprocal and not just the angular pattern. Hence, it is both simpler and more general than the argument that currently appears in the article. Moreover, the argument currently in the article says that "reciprocity requires that the power transfer is equally effective in each direction," which isn't a very precise statement of the reciprocity theorem.
Am I missing something?
—Steven G. Johnson 01:50, 3 September 2006 (UTC)
You wrote: Re. Circuitous; Sorry that wasn't a fair description. I meant do we need to go from the reciprocity theorem stated in terms of spatial integrals, down to a result for a single point, then (via our knowledge of the possible modes), to the amplitude of the signal (which is an integral over the feed cross-section). I suspect there must be a more direct way, because this method breaks down once we consider more than a handful of modes (because there will be no suitable point).
Yes, I do think you need to start from the reciprocity theorem stated precisely (i.e. as integrals of the fields/currents). The essential fact is this: you have to define what you mean by the "power" in a "channel", and in particular relate it to the fields. For a single mode, the power can be defined in terms of the field at any single point, so this is easy. For multiple modes/channels, you have to be able to decompose them somehow, which you normally do by orthogonality—that is, instead of using the field at a single point, you use an integral of the field against a mode pattern, or a current with the same pattern as the mode, so that you only couple to a single mode.
I would say that the theorem about the "radiation pattern" being reciprocal implicitly assumes a single operating mode in order for the "radiation pattern" to be uniquely defined. (There can be other modes, of course, but you can only use a single superposition of them in this simple version of the theorem.) As soon as you get to the more general multi-mode case you are really talking about the S-matrix, which should go into a separate article. My inclination would be to prove only the single-mode case in this article using the simple single-point argument, and refer to the (still to-be-written) S-matrix article for the multi-mode situation. (Or you can just prove the general S-matrix case on its page, and refer to reciprocity here as a special case. However, the single-mode case follows so simply from Lorentz reciprocity that I think it is probably worthwhile to prove it separately for pedagogical reasons.)
—Steven G. Johnson 21:13, 4 September 2006 (UTC)
I'm going to replace the article lead (?), to emphasize the distinction between the far-field pattern and the near-field pattern, and to reflect the fact that radiation pattern can mean either (I'll also make this distinction in the reciprocity section). Here's what I'm snipping out..
-- catslash 13:25, 7 September 2006 (UTC)
Thanks for the vote of approval - you'd better write a page on integrated optics now! There's still a lot to do on this page of course. -- catslash 14:46, 8 September 2006 (UTC)
I don't get the logic in the end of the proof: "Analysis of a particular antenna (such as a Hertzian dipole), shows that this constant is , where λ is the free-space wavelength. Hence, for any antenna". It seems to me like a generalization to the general from the particular that is not obvious. —Preceding unsigned comment added by 80.216.130.104 ( talk) 10:11, 7 March 2009 (UTC)
One question I always had on antenna gain plotting is the difference between rotating the antenna (with signal source attached) and recording the signal strength from a fixed location (same as walking around a fixed antenna with a receiver, taking the path of a constant radius circle and recording received signal strength), and walking around with a receiver and following the path of constant received amplitude. The latter is what you would see if the transmitted energy was visible, the true shape of the field in space. The former collects data about signal strength and therefore antenna gain at different angles, but if you plot it on linear or log scale, you don't get the real world spacial distribution of the energy. If you superimposed an antenna pattern on a map, and assumed that people (with a receiver of a certain threshold) could receive the signal if they were inside the pattern, it would be the latter pattern only that would work, not the standard log gain plot. In ideal space, the "walk around" iso-amplitude pattern would follow 1/r^2 rule after the antenna gain were applied in each direction. Another issue here is if, in the walk around process, you had an antenna null that caused you to travel into the near field area of the antenna, some strange things would happen. You would have to use enough power into the antenna so that your receiver would work everywhere outside the near field while walking the constant signal strength path.
I wish this Wikipedia article addressed these not so obvious issues with measuring and plotting radiation patterns. I personally don't feel qualified to do this. 192.80.95.243 ( talk) 16:33, 28 December 2010 (UTC)
Someone remarked the proof of this is long, but I don't see why such a proof is needed. That's a completely separate topic. You wont find the proof of the reciprocity theorem in any antenna book in a section devoted to the radiation pattern.
It just strikes me someone knows a proof of it, so they thought they would write it in the section on radiation pattern. IMHO, the reciprocity theorm should just be reffered to, and a link to it on another Wikipedia page. It is unneeded in a section on radiation pattern. Sure, it is helpful to know about it for antenna analysis, but so are dB too, and its useful to know what a transmitter is. Is there a need to explain all them?
IMHO, the whole section should be removed. Drkirkby ( talk) 23:15, 15 April 2012 (UTC)
The figure showing a rectangular radiation plot is mislabeled as showing directivity in dBi. It is actually showing a normalized power pattern in dB relative to peak, because a 0 dBi antenna can only be an isotropic radiator.