Fully-metallic Luneburg lenses for satellite communications at Ka-band

Authors: Oscar Quevedo-Teruel

Source: FERMAT, Volume 33, Communication 1, May.-Jun., 2019

Abstract: Luneburg lenses have a response that is very a suitable for antenna designs for satellite communications [1]. A Luneburg lens is a rotationally-symmetric graded-index lens that transforms a point source (cylindrical or spherical wave) into a plane wave at the opposite direction in which it is fed [2]. One excellent characteristic of Luneburg lenses is that they finalise with a refractive index of 1 at their contour. Therefore, a perfect matching with free space is achieved and no reflections at the borders are expected. Reflections in a Luneburg lens are only produced at the transitions between materials defined by the required discretization in a practical implementation. Although the original idea of Luneburg was to implement a dielectric lens, dielectric materials produce high losses when the frequency increases.

To overcome this limitation, non-Euclidean transformations were proposed to produce fully-metallic solutions [3-6]. This idea has recently been implemented for satellite communications in Ka-band [7]. In this case, a third dimension is used to produce the equivalent refractive index required for the lens, being all the propagation in air.

A second possibility consists of using periodic structures, also named metasurfaces, such as metallic pins with different heights to tailor the required refractive index [8,9]. Differently to these works, it has recently been proposed the use of periodic glide-symmetric holes [10,11]. Holey structures are easy to mill, and more costeffective than pin-type solutions. However, holes may require of small distances between plates to provide a sufficient increase of the equivalent refractive index [12]. In order to increase the distance between parallel plates, the refractive index provided by conventional holes was enhanced by using glide symmetry [13-15].

In this presentation, we describe these two techniques: non-Euclidean transformations and periodic structures; and we summarize their advantages and drawbacks.

Index Terms: Luneburg lenses, non-Euclidean transformations, glide symmetry, geodesic lenses, satellite communications, Ka-band, fully metallic lenses, beam-scanning, metasurfaces

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Fully-metallic Luneburg lenses for satellite communications at Ka-band