Shrinking a gradient-index-lens antenna system with a spaceplate

The miniaturization of optical systems is an ongoing challenge across the electromagnetic spectrum. While the thickness of optical elements themselves can be reduced using advances in metamaterials, it is the voids between these elements—which are necessary parts of an optical system—that occupy most of the volume. Recently, a novel optical element coined a “spaceplate” has been proposed, which replaces a region of free space with a thinner optical element that emulates the free-space optical response function—thus having the potential to substantially shrink the volume of optical systems. While there have been a few proof-of-principle demonstrations of spaceplates, they have not yet been deployed in a real-world optical system. In this work, we use a bespoke-designed spaceplate to reduce the length of a gradient-index- (GRIN) lens microwave antenna. Our antenna is designed to operate at 23.5 GHz and the incorporation of a nonlocal metamaterial spaceplate enables the distance between the antenna feed and the GRIN lens to be reduced by almost a factor of 2. We find that the radiation patterns from a conventional and space-squeezed antenna are very similar, with a very low cross-polarization, and only a minor increase in the side-lobe levels when introducing the spaceplate. Our work represents a demonstration of a spaceplate integrated into a real-world optical system operating in microwave spectral region, highlighting the potential for this concept to reduce the physical size of systems in applications including imaging, spectroscopy, radar, and communications.