I’m always running into interesting things while doing research for content here. Yesterday, I ran into something called the Luneburg Lens.
Let’s start with the picture:
A radar reflector can be made from a Luneburg lens by metallizing parts of its surface. Radiation from a distant radar transmitter is focused onto the underside of the metallization on the opposite side of the lens; here it is reflected, and focussed back onto the radar station. A difficulty with this scheme is that metallized regions block the entry or exit of radiation on that part of the lens, but the non-metallized regions result in a blind-spot on the opposite side.
This is an Edwards AFB, F-22 Raptor launching an AIM-9L Sidewinder during testing. If you look aft of the missile’s exhaust plume you’ll notice an odd shape dorsally mounted on the aircraft fuselage. At first you may think it’s a camera that mounted to record launch of the missile but it’s a device meant to enhance the radar signature of the aircraft, called a Luneburg Lens.
Luneburg Lenses are used in radar reflectors to enhance radar signature of low-observable aircraft to operate in airspace that’s being controlled/observed by air traffic control. Here’s a closer look on how it appears on the F-22:
It’s kind of a grainy image so we’ll try another view of the lens on the F-22:
Here’s a close-up (again apologizes for the graininess):
The Luneberg Lenses are also used in target drones such as this Teledyne-Ryan Firebee II drone (the lens appears above the forward wheel of the dolley and aft of the air intake):
In this case the Lenses are used to enhance the radar signature in order to more accurately simulate radar signature of threat aircraft.
I’m sure that most readers are already familiar but, since I don’t work in aerospace, I thought it was an interesting aside.