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Monday, April 15, 2013

Luneburg Lens

The Zeus Acquisition Radar and smaller Target Track Radars on Kwajalein Island, Republic of the Marshall Islands

The idea of a 1,000 ton radar unit piqued my curiosity, so I looked into it a little bit. I was picturing some giant radar dish mounted on giant pivots being pushed around by giant hydraulic rams. Not the case. It's more like a building, a large static structure that just sits there. Nobody measures buildings by weight, well, except reporters maybe. Anyway the thing is more like one of the Elephant Cage antennas that the US armed forces built for radio direction finding. So it was big and no doubt expensive, but there were no giant hydraulics. Darn.



    Luneburg Lens was the operative principle, although Luneburg envisioned a sphere and what we are using is more like a truncated cylinder, i.e. shaped like a tuna can. The Luneburg Lens would be really cool if anyone could ever build one, but as near as I can tell it is only a theoretical construct. Supposedly it would work equally well for any kind of electromagnetic radiation: light, radio, microwave, or as in this case, RADAR. Obviously you would need different materials for different kinds of radiation, but the principle is the same. However, as far as I can tell, no one knows how to create a substance whose index of refraction varies continuously and evenly from one point to another, which is what you need to make one of these things. Some people are making stepwise approximations of them for RF (radio waves), and some other people tried to make a better one using foam, but it didn't work out so well.


    There is one other issue that I wonder about. Supposedly a Luneburg Lens focuses the radiation on its outside surface, so you need to have your detector out side this giant circular cage, and you need to move it around in order to determine the direction of your signal, but I haven't come across any mention of traveling detectors. So maybe they just had a bunch of fixed detectors all operating simultaneously. I suppose that might work better. Just look at the signal strength meters and you could tell which direction your target was.

2 comments:

Anonymous said...

There was a High Frequency radio wave version of the Luneburg Lens antenna used by FAA/FCC and was pictured in a manufacturing brochure of long ago ('60s).
Zoom into Kodiak, AK and look at the island just SW of there, for what it looked like.
DOD chose the elephant cages known as CDAA or CDAA.
Pat Ryan KC6VVT

KC6VVT Blog said...

Use sat view at:

https://maps.google.com/maps/ms?msid=214921740929160404673.0004e64796ef673fdd399&msa=0&ll=57.775044,-152.339891&spn=0.002251,0.004823