Optical nanoantennas with tunable radiation patterns.

We address new optical nanoantenna systems with tunable highly directional radiation patterns. The antenna comprises a regular linear array of metal nanoparticles in the proximity of an interface with high dielectric contrast. We show that the radiation pattern of the system can be controlled by changing parameters of the excitation, such as the polarization and/or incidence angles. In the case of excitation under the total reflection condition, the system operates as a nanoscopic source of radiation, converting the macroscopic incident plane wavefront into a narrow beam of light with adjustable characteristics. We derive also simple analytical formulas which give an excellent description of the radiation pattern and provide a useful tool for analysis and antenna design.