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We study the directional properties of a radiation field emitted by ageometrically small system composed of two identical two-level emitters locatedat short distances and driven by an optical vortex beam, a Laguerre-Gaussianbeam which possesses a structured phase and amplitude. We find that the systemmay operate as a nanoantenna for controlled and tunable directional emission.Polar diagrams of the radiation intensity are presented showing that a constantphase or amplitude difference at the positions of the emitters plays anessential role in the directivity of the emission. We find that the radiationpatterns may differ dramatically for different phase and amplitude differencesat the positions of the emitters. As a result the system may operate as a two-or one-sided nanoantenna. In particular, a two-sided highly focused directionalemission can be achieved when the emitters experience the same amplitude and aconstant phase difference of the driving field. We find a general directionalproperty of the emitted field that when the phase differences at the positionsof the emitters equal an even multiple of \pi/4, the system behaves as atwo-sided antenna. When the phase difference equals an odd multiple of \pi/4,the system behaves as an one-sided antenna. The case when the emittersexperience the same phase but different amplitudes of the driving field is alsoconsidered and it is found that the effect of different amplitudes is to causethe system to behave as a uni-directional antenna radiating along theinteratomic axis.

Radiation pattern of two identical emitters driven by a Laguerre-Gaussian beam: An atom nanoantenna