Microwave superdirectivity with dimers of helical elements

Abstract

Superdirective end-fire radiation in the low GHz frequency range is demonstrated using magnetically-coupled structures of subwavelength metallic helices. 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) and provide close to theoretical maximum values of directivity without using complex feeding networks. The size, directivity, efficiency and operational passband width of such structures is optimized.