Shrinking a gradient index lens antenna system with a spaceplate

TL;DR

This paper demonstrates the integration of a spaceplate into a microwave gradient index lens antenna, effectively halving its length while maintaining similar radiation patterns, showcasing a practical step towards miniaturizing optical systems.

Contribution

It presents the first real-world application of a spaceplate in a functional optical system, reducing antenna size without significantly affecting performance.

Findings

A spaceplate can nearly halve the antenna length.

Radiation patterns remain similar with low cross-polarization.

Minor increase in side-lobe levels observed.

Abstract

The miniaturisation 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' was proposed, that 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 two. We find the radiation patterns from a conventional and space-squeezed antenna are very similar, with a very low cross-polarisation, and only a minor increase in the side-lobe levels when introducing the spaceplate. Our work represents a first example of a spaceplate integrated into a functional optical system, highlighting the potential for this concept to reduce the physical size of optical systems in real-world applications.