Twin Spherical Antennae - What For?

To better penetrate aluminum foil hats ?>:-} ...Jim Thompson

I can see you have already been penetrated.

Getting back to my serious question, here is one example.

Klaus

Kirtland AFB? There's your answer >:-} ...Jim Thompson

Specified in IEC 61587-3 Part 3 for testing electromagic shielding: With the transmitter (or receiver) inside the sphere, it makes a rather good test source for producing a specific field strength, over a very wide frequency range, without having the test equipment interfere with the test.

However, the van is a very different application than for testing rack or box shielding. My guess(tm) is that the van was making measurements of ambient RF radiation levels and someone with a big budget demanded extreme accuracy.

That sounds like tracking microwave dishes. Dishes for geostationary satellites are a hemisphere so the ones you saw are probably for polar orbit satellites or ground stations.

The van could be a comms repeater.

Here are two other possiblities:

Spherical phased array antenna.

Luneburg lens antenna. Interesting design.

Here is an animation.

"4. the optical beam forming is inherently wide band, giving true time-delay beam forming throughout;

1. multiple beams and beam steering are simply achieved as outlined above."

Looks like a good canidate for adaptive beamforming. Capable of simultaneous beams and precise tracking during vehicle movement.

But what would two of them be doing on top of a van? Seems too exotic for just an EMI monitoring operation.

I do recall seeing a paper describing a surveillance system using reflected microwaves. Something analogous to the old laser on a window trick.

Klaus Jensen

If it is spherical, it would be an odd thing to rotate. Those antennas are usually already omnidirectional.

You already have half a dozen guesses. I suppose I could add the egg beater antenna, but they are more like two loops rather than a sphere.

This is a very common antenna for satcom. Military, hams, weather satellites, etc. For satellite work, it is useful up to UHF frequencies.

Nope. There are such constructs, where the phase shifters are liberally plastered all over the surface of the sphere. The big advantage is that it will track multiple targets coming from almost any direction. However, mounted on a van, that makes no sense as everything below the level of the horizon, will end up looking at the ground or the roof of the van.

Nope. A Luneburg lens is made from multiple layers of plastics and ceramics. The net result is a dielectric lens. There's nothing inside the sphere except dielectric material. Any receiver, probe, waveguide horn, or sensor would need to be attached to the OUTSIDE of the sphere in order to benefit from the dielectric lens gain. If one covers that entire surface of the sphere with electronics, there's no open space on the other side to view the target. This is what it looks like in practice. Note the external horn and LNB: More:

Also, with two of these spheres on the van roof, I would expect them to block each other's view of the horizon. Only pointing somewhat up is clear.