Talk:Parabolic antenna

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Untitled[edit]

I wanted to include the gain equation, but ended up re-writing the article to add links to other antenna topics. My apologies to the original author for this usurpation. Also, it tacked my IP address on as my username rather than k7jeb, which I got after the article went to press. Jim, K7JEB, amateur radio...

Major edit[edit]

I made some corrections to the part about off-set and Cassegrain antennas. Miikka - the off-set antenna feed does illuminate the entire reflector PLEASE NOTE. The diagram showing the three antenna types should identify the bottom antenna as Gregorian and not Cassegrain (see my edits). I don't have a graphics editor here that handles .PNG files, so I was not able to correct the diagram.

Regards, KI6JA - Sherrel 04:39, 19 July 2007 (UTC)[reply]

This page needs a major edit. Perhaps sections could be written on parabolic antennas used specificly with radio-astronomy, Wi-Fi and satellite-tv, them being the most common applications currently. I added a few basic drawings as well as paragraphs on structure and feeding. Also a description and comparison of general antenna characteristics should be added. Again from different perspectives: professional, amateur-radio, military signal and consumer equipment... OH3GPJ --Miikka Raninen 23:23, 14 April 2006 (UTC)[reply]

It seems to me that, rather than focus on individual applications of this antenna type, the article should draw together the common features exhibited across the application-specific designs. The fields of application should be mentioned in passing, but not have individual paragraphs dedicated to them.

But this being Wikipedia, there's nothing stopping anyone from adding whatever points they feel are necessary to the article. Jim, K7JEB 01:09, 16 April 2006 (UTC)[reply]

Jim, I am assuming that in the GAIN equation, G is linear (not dB) and measurements are metric (as in meters) ? boB K7IQ (talk) 06:08, 24 October 2022 (UTC)[reply]

File:Parabolic antenna types.png[edit]

The image caption for the third diagram says its "Cassegrain" but the diagram shows a Gregorian design and the image talk page says its Gregorian[1]. 75.197.132.10 (talk) 20:50, 3 April 2009 (UTC)[reply]

Units[edit]

There are no units, and the units of gain are often ambiguous (dB's?) —Preceding unsigned comment added by 92.8.52.42 (talk) 09:18, 8 April 2010 (UTC) this happens[reply]

Parabolic "antenna" vs. parabolic reflector, or perhaps parabolic dish?[edit]

Since the parabolic dish in this context serves only a reflector of RF energy, you should consider changing the actual title to either of these terms, since both are more accurate than "parabolic antenna." The actual antenna (i.e. the RF transducer) is usually placed at the focus. The reason that this matters is because the parabolic dish shape will bring many forms of collimated energy to a focus - light, sound, radiowaves, etc. This is one of the reasons that RF reflectors are never left shiny or painted with glossy paint - the heat generated by reflected and focused sunlight could destroy an LNA! — Preceding unsigned comment added by 129.55.200.20 (talk) 18:50, 13 February 2013 (UTC)[reply]

The usage in electrical engineering is "parabolic antenna". Also, as you point out, "parabolic reflectors" and "parabolic dishes" are used with many types of radiation. If the contents of this article, and all the other uses of parabolic reflectors, such as reflecting telescopes and parabolic microphones, were merged into the Parabolic reflector article, it would be huge and confusing. This article's scope is limited to radio wave antennas that use parabolic reflectors, and there is certainly enough content in this topic to merit a separate article. --Chetvorno^TALK 21:40, 13 February 2013 (UTC)[reply]

Technically, the antenna is the driven element at the focus of the parabola. However, the driven element of a yagi for example is not considered the only part of the antenna with the rest just being reflectors, etc., so I suppose the driven element of the dish plus the dish is fair to consider as an "antenna system" shortened to antenna... --ssd (talk) 14:51, 14 April 2013 (UTC)[reply]

Yes, many types of antennas, such as the horn antenna, loopstick, reflective array antenna, ground plane antenna, corner reflector, curtain array, patch antenna, dielectric resonator antenna, beam waveguide antenna, backfire antenna etc. include "passive" elements in addition to the "driven element" or "feed antenna" which actually produces the radio waves. The passive elements serve to direct the radio waves into the desired radiation pattern, and are considered integral parts of the antenna, which is not just limited to the "driven element". --Chetvorno^TALK 17:24, 14 April 2013 (UTC)[reply]

Plane wave vs. near field for parabolic antennas[edit]

The article states that a plane wave is emitted by the parabolic reflector. As such, a parabolic antenna should not have a near field. Yet various sources (e.g. RECOMMENDATION ITU-R BS.1698, section 2.2.4.1) indicate the presence of a near field and a transition to a far field based on the distance where the phase error drops to an accepted value. It would be helpful if this issue were addressed in the article. 70.83.121.105 (talk) 04:58, 13 May 2017 (UTC)[reply]

That's a good point. To create the narrow beamwidths which justify the expensive parabolic dish, parabolic antennas usually start at apertures of 5-10λ. With focal ratios (f-numbers) of 0.25-0.8, the focal length of the dish is virtually always over a wavelength, in the far field. In order to get the most resolution out of the dish, the feed antenna must act as a point source, and so the reflector must be in the far field of the feed. For smaller antennas the parabolic construction would not be economical, and cheaper corner reflector antennas or reflective array antennas would be used instead. I agree, this should be in the article. --Chetvorno^TALK 21:21, 13 May 2017 (UTC)[reply]

misleading sentence[edit]

The article says: "The 100 meter Green Bank Radio Telescope at Green Bank, West Virginia, the first version of which was completed in 1962, is still the world's largest fully steerable parabolic dish." This is misleading. The first version was only the largest steerable telescope for a few years, after which the Effelsberg telescope held the title for tens of years, before Green Bank's rebuild. Scummos (talk) 10:01, 22 June 2017 (UTC)[reply]

External links modified (January 2018)[edit]

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Qualitative terminology in feed antenna polarization section[edit]

I love this article! But the section on feed antenna polarization uses the adjective "severe." I would like additionally typical quantitative loss in dB. Is "severe" different from the typical loss for wrong polarization of a dipole? Idk! And what about circular polarization? 71.222.73.246 (talk) 00:05, 7 November 2022 (UTC)[reply]