Enhanced emission and light control with tapered plasmonic nanoantennas
  We introduce a design of Yagi-Uda plasmonic nanoantennas for enhancing the antenna gain and achieving control over the angular emission of light. We demonstrate that tapering of antenna elements allows to decrease spacing between the antenna elements tenfold also enhancing its emission directivity. We find the optimal tapering angle that provides the maximum directivity enhancement and the minimum end-fire beamwidth. 
Ivan S. Maksymov, Arthur R. Davoyan and Yuri S. Kivshar
physics.optics