The YouTube video in the WIRED article Inside Facebook’s First Efforts to Rain Internet from the Sky shows a dish antenna (starting after 02:00) with what looks like a Cassegrain secondary reflector. The context of the video and article suggests it is for testing E-band millimeter-wave data up/down link to an aircraft (about 60 to 90 GHz according to the article, or 5 to 3 millimeter wavelength).

I noticed that the secondary mirror is spinning. By watching the wobble and checking individual frames it seems to be turning at at least 4 revolutions per second. It could be much faster and aliasing makes it look this slow.

I can not think of any reason why this would be turning. It's rotating about the optical axis, so it's not switching between primary and secondary horn locations.

Why is the reflector on this millimeter-wave antenna spinning?

above: GIF made from extracted and cropped frames from this WIRED YouTube video.

above: Right-click for larger view; Ground station for millimeter-wave data linking to aircraft, from WIRED. Photo credit Damon Casarez.

The WIRED YouTube video Inside Facebook's Quest to Beam the Internet Via Solar Drone and article Inside Facebook’s First Efforts to Rain Internet from the Sky show a dish antenna (starting after 02:00) with what looks like a Cassegrain secondary reflector. The context of the video and article suggests it is for testing E-band millimeter-wave data up/down link to an aircraft (about 60 to 90 GHz according to the article, or 5 to 3 millimeter wavelength).

I noticed that the secondary mirror is spinning. By watching the wobble and checking individual frames it seems to be turning at at least 4 revolutions per second. It could be much faster and aliasing makes it look this slow.

I can not think of any reason why this would be turning. It's rotating about the optical axis, so it's not switching between primary and secondary horn locations.

Why is the reflector on this millimeter-wave antenna spinning?

above: GIF made from extracted and cropped frames from this WIRED YouTube video.

above: Right-click for larger view; Ground station for millimeter-wave data linking to aircraft, from WIRED. Photo credit Damon Casarez.

The YouTube video in the WIRED article Inside Facebook’s First Efforts to Rain Internet from the Sky shows a dish antenna (starting after 02:00) with what looks like a Cassegrain secondary reflector. The context suggests it is for testing millimeter-wave data up/down link to an aircraft.

I noticed that the secondary mirror is spinning. By watching the wobble and checking individual frames it seems to be turning at at least 4 revolutions per second. It could be much faster and aliasing makes it look this slow.

I can not think of any reason why this would be turning. It's rotating about the optical axis, so it's not switching between primary and secondary horn locations.

Why is the reflector on this millimeter-wave antenna spinning?

above: GIF made from extracted and cropped frames from this WIRED YouTube video.

above: Full frame extracted from this WIRED YouTube video.

The YouTube video in the WIRED article Inside Facebook’s First Efforts to Rain Internet from the Sky shows a dish antenna (starting after 02:00) with what looks like a Cassegrain secondary reflector. The context of the video and article suggests it is for testing E-band millimeter-wave data up/down link to an aircraft (about 60 to 90 GHz according to the article, or 5 to 3 millimeter wavelength).

I noticed that the secondary mirror is spinning. By watching the wobble and checking individual frames it seems to be turning at at least 4 revolutions per second. It could be much faster and aliasing makes it look this slow.

I can not think of any reason why this would be turning. It's rotating about the optical axis, so it's not switching between primary and secondary horn locations.

Why is the reflector on this millimeter-wave antenna spinning?

above: GIF made from extracted and cropped frames from this WIRED YouTube video.

above: Right-click for larger view; Ground station for millimeter-wave data linking to aircraft, from WIRED. Photo credit Damon Casarez.