  A Yagi-Uda-like optical nanoantenna concept using resonant core-shell
plasmonic particles as its "reflectors" and "directors" is studied numerically.
Such particles when placed near an optical dipole source in a certain
arrangement may exhibit large induced dipole moments, resulting in shaping the
far-field radiation pattern, analogous to the far field of classical Yagi-Uda
antennas in the microwave regime. Variation of the ratio of radii in concentric
core-shell nanostructure is used to tailor the phase of the polarizabilities of
the particles, and consequently the antenna's far-field pattern. The idea of a
nanospectrum analyzer is also briefly proposed for molecular spectroscopy.
