The extraordinary radiation pattern of an optical rod antenna

We investigated the radiation pattern of an optical rod antenna and found that it had many features compared with its conventional radio-wave equivalents. After defining a parameter {\Lambda} = {\lambda}eff /{\lambda}, which was the ratio of the effective wavelength of the rod antenna to the incident wavelength, we found that {\Lambda} had a great influence on the radiation pattern. Even the radiation pattern with a higher resonant order is without side lobes and results in a sharper directivity, which provides new design flexibilities in improving the directivities of the optical antennas.