Three-dimensional large-aperture lens antennas with gradient refractive index

We propose an accurate method for designing three-dimensional (3D) large-aperture metamaterial slab lens antennas with gradient refractive index (GRIN). According to the geometric optics, Fermat principle, ray-tracing technique and impedance matching, the 3D GRIN slab lenses with large apertures are accurately designed and simulated. With the aid of the effective medium theory, an X-band and a Ku-band conical horn antennas loaded with the 3D GRIN slab lenses of 250-mm diameter are experimentally realized using the drilling-hole technique on the printed circuit boards (PCBs) as the unit cells of metamaterials. Compared to the traditional dielectric lens with the same aperture, the proposed antennas have very good performance with high directivity, and the gain is increased by 2 to 5 dB. Using the same method, we design and realize a huge-aperture GRIN lens in the X band with a diameter of 1000 mm, which is composed of nearly one millions of inhomogeneous unit cells of square-ring resonators and dielectric blocks with drilling holes. Due to the huge aperture size, the electromagnetic ray paths inside and outside of the GRIN lens are verified and optimized using the ray tracing technique. Measurement results show good performance of the proposed antenna with high directivity.