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The images below are of actual OneWeb satellites or models. There are two disk-like appendages and an array of linear gizmos which may be an array antenna.

Is it possible to explain how these two types of structures work in some detail? Are the linear ones pointed at the ground? Do they steer electronically, and if so why is each row at a different fixed angle? Do the disks talk to adjacent satellites? Do they steer?

A model replica of a OneWeb satellite Regis Duvignau / Reuters

above: From the New York Times article OneWeb to Launch 34 Satellites as Astronomers Fear Radio Chatter "A model replica of a OneWeb satellite. Credit: Regis Duvignau / Reuters" below x2: from Aerospace Technology's OneWeb Satellite Constellation

click for full size:

enter image description here enter image description here

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above: Cropped, rotated and sharped from www.ww01.net/en's Three ground stations will be built in China. What information does the “OneWeb” China Bank disclose?. below: From Caixin/com's U.K. Satellite Firm OneWeb Pushes Into China Market in Search of Scale

U.K. Satellite Firm OneWeb Pushes Into China Market in Search of Scale

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    $\begingroup$ It looks like a one-man-band getup with accordion and cymbals. media.gettyimages.com/photos/… $\endgroup$
    – Organic Marble
    Feb 6, 2020 at 23:02
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    $\begingroup$ Omg it does! Something seemed familliar; you've nailed it! $\endgroup$
    – uhoh
    Feb 6, 2020 at 23:03
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    $\begingroup$ English is not my first language, but I would prefer "how do" instead of "how to". But I may be wrong. $\endgroup$
    – Uwe
    Feb 7, 2020 at 16:26

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A complementary "rough" analysis to @prop-a-gator answer (taking as granted that a phased-array design was used):

  • The first step is to find the antenna designed beam pattern. It is given in OneWeb's application to FCC1, the so-called "Attachment A, Technical Narrative", Page 12, Fig A.3-1.

We can see that the pattern consists of 16 elliptical beams. To facilitate discussions, number these beams from 1 to 16 in the direction North-South.

enter image description here

  • The second step is to correlate the beams diagram to the antenna system in the picture.

In the picture, we can recognize 16 "rods", so we can logically infer that each "rod" is to produce one of the 16 elliptical beams. The 16 "rods" need to be "tilted" appropriately from the nadir direction to produce the pattern of 16 adjacent beams. The 2 middle rods correspond to the two external beams (1 & 16), hence their large relatve angle. The two external rods correspond to the 2 adjacent beams, each side of the nadir (8 & 9). We can assume that this particular arrangement facilitates the spill-over between adjacent "rods".

Those who are skilled in antenna design can guess the dimension of an equivalent aperture for each beam (the frequency is Ku-band) and correlate that with the dimension on the picture (if the dimension of the satellite is known).

1I do not have a direct link. But here is a way to download the document from the FCC site: Go to the OneWeb filing page of the FCC. On that page, find "Document View". Under it, you should have a link called "Attachment Menu". The "Technical Narrative" is in one of these attachments.

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    $\begingroup$ I do not have a direct link. But here is a way to download the document from the FCC site: Go to the OneWeb filing page of the FCC. On that page, find "Document View". Under it, you should have a link called "Attachment Menu". The "Technical Narrative" is in one of these attachments. $\endgroup$
    – Ng Ph
    Aug 12, 2021 at 21:21
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    $\begingroup$ Using 3.3 beam-widths = 223 km or beam-width of 67 km and an altitude of 1200 km I get $\theta$ = 3.2 degrees. $\theta = 1.22 \lambda/d$ suggest the bars are about 22 wavelengths tall. At $f$ = 15 GHz or $\lambda$ = 2 cm for example, that makes them about 44 cm. We don't know what the contours represent exactly, but if these are 150 kg spacecraft then that certainly sounds to be in the right ballpark. Thanks! $\endgroup$
    – uhoh
    Aug 12, 2021 at 22:48
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    $\begingroup$ @uhoh, the technical document ("Technical Narrative") says they are -3dB contours (page 11). Anyway, the angles are given in Fig. A.3-1. They don't specify the frequency of the plotted beams, but the ranges are given in the document (Table A.2-1, page 4). If they plotted the satellite transmitted beams, the frequency is in 10.7-12.7 GHz. $\endgroup$
    – Ng Ph
    Aug 13, 2021 at 9:43
  • $\begingroup$ Thanks! I'll leave a refined calculation to someone more "skilled in the art". :-) $\endgroup$
    – uhoh
    Aug 13, 2021 at 10:29
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    $\begingroup$ @uhoh, Yep. Indeed, "the purpose of computing is insight, not numbers" (can't remember who said that). $\endgroup$
    – Ng Ph
    Aug 13, 2021 at 11:02
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I might be mistaken, but when I went through OneWeb architecture proposals, they were ditching the idea of Inter-Satellite-Links (ISLs), while it would make their satellites more expensive, heavier and generally more complex. But this can be an outdated information.

Answering other questions:

According to my colleague who have way more experience in Telecommunication, those are indeed phased arrays and they would look down to Earth. The sole purpose of them placed at certain fixed angles is to reduce the impact of the gain loss due to the electronic steering. So consider it as a 'mechanical' pre-steering. For instance, some Satcom-on-the-move terminals are also utilize the mechanical pre-steering, because electronic steering is limited and will provide poor results for very steep angles.

EDIT: Addressing the Uhoh's comment: at the moment, I was able to find single source that mentions the combination of mechanical and electrical beam steering for the Satcom-on-the-move terminal. Link is here. See section 4.7.4.2 and figure 4.23 (B). However, there are plenty of mechanical vs electrical tilt discussions, which are rather related to the terrestrial comms. Example here. See the 'what is Tilt?' section. It is also mentioned there that combination of both mechanical and electrical tilting at the same time might help you to satisfy your goals for a smaller budget.

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    $\begingroup$ I will ask my colleague, if he have some examples in mind. ISLs are Inter-Satellite-Links, I will edit it in my answer. $\endgroup$
    – prop-a-gator
    Feb 7, 2020 at 10:38
  • $\begingroup$ that's great, thanks! $\endgroup$
    – uhoh
    Feb 7, 2020 at 14:03
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    $\begingroup$ I'd like to click accept on your answer; is there any chance you can find at least a minimal supporting source or citation that mentions that these are phased arrays? Thanks! $\endgroup$
    – uhoh
    Feb 23, 2020 at 6:20
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    $\begingroup$ I believe that OneWeb keeps their antenna design as a commercial secret, so there is no way to we can 100% prove that those are phased arrays. However, considering their goal to serve as many users as possible, one may speculate that they would try to maximize the amount of connections per single satellite, hence the throughput. And besides, there are no other visible elements on the satellite that can serve that purpose (I don't believe those two horns are the main comms payload). $\endgroup$
    – prop-a-gator
    Feb 24, 2020 at 9:13
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    $\begingroup$ Now after I checked the Aerospace-Technology's article, it is stated there that: 'Other payloads onboard include two TTC omni antennas, two Ku-band antennas, two Ka-band antennas, and a three-axis stabiliser.' From that, I assume that those two horn/dishes are also part of comms payload (as for TTC only omni antennas are going to be used). $\endgroup$
    – prop-a-gator
    Feb 24, 2020 at 10:21
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I'm late to the party, but here's the link to the technical description: https://licensing.fcc.gov/cgi-bin/ws.exe/prod/ib/forms/attachment_menu.hts?id_app_num=108859&acct=510261&id_form_num=12&filing_key=-284244

Pick the "Attachment Technical Narrative" for a pdf with all the details.

From my reading of the document, I concluded:

  • The earlier answers were exactly right about the linear arrays on the nadir side of the satellite, and they handle satellite-to-user links at Ku-band. Although it's not obvious from the model, each is gimbaled and able to independently track different ground stations.
  • The two dish antennas are for satellite-to-ground-station links at Ka-band.
  • There is no mention of inter-satellite links.
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  • $\begingroup$ "Although it's not obvious from the model, each is gimbaled and able to independently track different ground stations." I think you mean the Ka dishes? From the linked document: "Each OneWeb satellite will have 16 nominally identical user beams, operating in Ku-band, each consisting of a non-steerable highly-elliptical spot beam5" $\endgroup$
    – Steve
    Nov 13 at 18:18
  • $\begingroup$ I think the gimbaled dishes are the Ku-band cross links. First of all, the satellites move relative to each other, so the antennas need to track that motion. Second, I'm pretty sure that the beam pattern shown in an earlier pattern is fixed with respect to the spacecraft body. The spacecraft points at nadir, and as it moves north to south in its orbit the beam pattern moves across the ground. In the third photo of the question, you can see 2 flat blue objects canted relative to the body. Those are fixed slotted waveguide antennas to generate the antenna pattern I just mentioned. $\endgroup$
    – John McCarthy
    Nov 14 at 19:51
  • $\begingroup$ If you mean the 2 sets of 8 canted antennas, then I think the statement above I shared applies: "Each OneWeb satellite will have 16 nominally identical user beams, operating in Ku-band, each consisting of a non-steerable highly-elliptical spot beam". In your answer, you say "they handle satellite-to-user links at Ku-band. Although it's not obvious from the model, each is gimbaled" These statements directly conflict. $\endgroup$
    – Steve
    Nov 14 at 20:12
  • $\begingroup$ The two Ka dish antennas are gimbaled, due to the motion around the Earth and the ground stations being in fixed locations. You mention in your comment "Ku band cross-links", but in your answer you say "no mention of inter-satellite links". I think this is because they dropped that whole idea and just use the ground stations. $\endgroup$
    – Steve
    Nov 14 at 20:14
  • $\begingroup$ Steve, I think you're right. Thanks for the information. $\endgroup$
    – John McCarthy
    Nov 15 at 21:10

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