Phys. Rev. X 7, 031017 (2017)

The realization of highly directional antennae with needle-like radiation patterns would be useful for communication between multiple transmitters and receivers, and researchers have long considered ways to achieve such a feat. Recently, significant progress has been made with the realization of micro- or even nanoscale directional antennae based on dielectric and metallic nanoparticles. However, in miniaturized systems it has proven difficult to achieve extreme directivity due to the physical limitations and difficulty in fabricating structures. Now, Richard Ziolkowski from University Technology Sydney in Australia has theoretically demonstrated how to achieve true needle-like radiation from currents driven on a spherical surface. Importantly, limitations on how small the sphere can be, and still achieve good directivity, are defined. Ziolkowski investigated a variety of Huygens source set-ups and superdirective radiation is predicted from an annular array of dielectric resonators. This design of dielectric resonator antenna is a good candidate for experimentally realizing a Huygens multipole system as it should be feasible to fabricate. The antenna concept may have applications not only for communications but also for subwavelength imaging.