VLA’s Original Hybrid Lens
The original design of the Very Large Array antennas used a hybrid lens between the subreflector (bowl at top) and the receivers (off camera below).
This strange-looking contraption gathered radio waves coming off the subflector into tighter formation before they entered the narrow funnels (feed horns) on the receivers. The nested rings in the center of this structure act like a Fresnel lens to bend inward radio waves that are farthest apart and slow down radio waves in the very middle to keep in formation. The ring of cylinders act like wave guides for the important 21-cm waves that come from neutral hydrogen.
Credit: NRAO/AUI/NSF
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