  We report unidirectional radiation of a magnetic dipole above planar metal
surface, the radiation direction can be manipulated via changing the distance
between the dipole and the surface. This phenomenon is unique for the
combination of magnetic dipole and metal surface and does not happen for linear
polarized dipole on metal surface or magnetic dipole on dielectric surface. The
underlining physics is analytically disclosed by the interference of two
orthogonally-oriented dipole component with \pi/2 phase lag. A substantially
different mechanism of introducing the vectorial nature of the dipole itself to
control light emission distinguishes the present scheme from nanoantenna and
provides a new degree of freedom in light emission engineering.
