Superdirective Antennas of Coupled Helical Elements

Using magnetically-coupled structures formed of subwavelength metallic helices, we demonstrate superdirective end-fire radiation in the low GHz frequency range. Numerical, experimental and analytical results are presented on superdirective dimers that are almost three times smaller compared to previously demonstrated dimers of split-ring-resonators (0.09λ compared with 0.25λ). Optimisation of such structures in terms of their size, directivity, efficiency and operational passband is demonstrated.