Low-Profile Fully Metallic Multiple-Ridge Luneburg Lens Antenna

The geodesic Luneburg lens has been revisited as a suitable solution for some applications requiring directive beams in the millimetre wave band. Among its advantages, its rotational symmetry and high efficiency stand out. However, one of its drawbacks is the need for a certain height to produce the desired focusing properties of the lens. Here, we propose a low-profile solution based on rotationally-symmetric ridges that mimic, similarly to geodesic lenses, the effective refractive index of a Luneburg lens. Moreover, we show that both rectangular and trapezoidal ridges perform similarly, opening the possibility for other manufacturing techniques. We demonstrate this concept with a prototype that is fully-metallic and provides a scanning range of ±62° over a broad band of operation, from 24 GHz to 34 GHz. In this prototype, the height of the lens is 18 times more compact than the original Rinehart-Luneburg lens, allowing the lens to be vertically stacked, which is beneficial, for example, for producing linear arrays. This technique could be used to produce other type of lenses.