Ultracompact all-dielectric superdirective antennas
  We demonstrate a simple way to achieve superdirectivity of electrically small antennas based on a spherical dielectric particle with a notch. We predict this effect theoretically for nanoantennas excited by a point-like emitter located in the notch, and then confirm it experimentally at microwaves for a ceramic sphere excited by a small wire dipole. We explain the effect of superdirectivity by the resonant excitation of high-order multipole modes of electric and magnetic fields which are usually negligible for small perfect spherical particles. 
Alexander E.Krasnok, Dmitry S.Filonov, Pavel A. Belov, Alexey P.   Slobozhanyuk, Constantin R. Simovski, Yuri S. Kivshar
physics.optics physics.class-ph