Luneburg Reflector
Stealth performance is critical in stealth aircrafts but it is good that the aircrafts be visible at appropriate times. To be able to appear at will on radars, these aircrafts are equipped with a very special device: the Luneburg Lens.
What is a Luneburg Lens?
The Luneburg Lens is an ellipsoidal multi-refractive lens, partially coated with a metallic reflective layer. This enables it to focus incident electromagnetic waves of pre-determined wavelengths and reflect them back in the direction of the original ray wave. When any radar wave passes through the lens, the focusing characteristics make the radar cross-sectional area (RCS) reflected by the lens much larger than its physical cross section. This feature makes the Luneburg Lens extremely useful as a radar reflector to manipulate RCS.
Working principle of Luneburg lenses
RCS can be increased with Corner reflectors constructed from several perpendicularly placed metal strips which are simple in construction and cheaper in cost. Why use complex Luneburg Lens?
It is because, compared to corner reflectors, Luneburg lenses are smaller and lighter, inducing less drag and have no impact on aerodynamics. They are also better reflectors with better directional pattern, lower side and back lobes.
Luneburg reflectors on a F-35
While stealth capability improves survivability of stealth fighters, there is always the danger of accidents such as collision when the aircraft cannot be detected by air or ground radar, especially while flying in friendly airspace. Adding a Luneburg lens allows monitoring by air and ground radars whenever needed and alleviates such potential incidents.
Furthermore, stealth fighters with Luneburg lens gives added capability of deception. By manipulating RCS, the true radar signature of the aircraft can be denied. This is particularly useful in information warfare. Deploying Luneburg lenses not only conceals stealth fighter radar signature, but also prevents anti-stealth experiments by adversaries. The Luneburg Lenses are removable during wartime when full stealth mode is required.
