Super directive Yagi–Uda nanoantennas with an ellipsoid reflector for optimal radiation emission

Abstract

In this paper, the optimal designs of silicon Yagi–Uda nanoantennas (NAs) with an ellipsoid reflector have been proposed and analyzed using the 3D finite-difference time-domain method. The combination of nanospheres, nanowires, and ellipsoid reflectors has been employed to enhance the antenna directivity. The nanoantenna geometrical parameters are optimized using the particle swarm optimization algorithm. The optimized spherical NA with an ellipsoid reflector shows high directivity of 19.89, which is higher than the conventional counterpart by 65.75%. This enhancement is attributed to the different supported modes by the ellipsoid reflector, which increases the forward radiation and suppresses the backward one. Further, the optimized nanowire design with an ellipsoid reflector has achieved a directivity of 23.4. In addition, the radiation efficiency has been increased to 80.2% and 75.9% for optimized spherical and nanowire antennas, respectively. This enhancement is attributed to the efficient coupling between array elements as well as reduced sidelobe and back-lobe levels.