Superdirective mixed-multipole-based unidirectional spherical dielectric lens antennas

Studies of superdirective dielectric lens antennas are reported emphasizing unidirectional properties. The developed antennas are based on the higher-order transverse electric and magnetic modes present in a multilayered sphere realized with high-permittivity dielectrics. The superdirective properties of the lenses are empowered by exciting them with a basic unidirectional mixed-multipole antenna. Genetic algorithm optimization was employed to identify configurations that yielded both large directivity and front-to-back ratio outcomes. The analytical evaluations of several example systems of spheres having different outer radii, numbers of layers, and permittivities are described. Their radiated field patterns are presented along with comparisons with known directivity bounds to confirm their superdirective performance characteristics. Subsequent numerical assessments with commercial full-wave finite-element simulations of more realistic versions of several selected examples illustrate their potential for experimental realization.