  We calculate the beaming of coherent emission by means of geometrical optics.
When spherical elementary waves are phase-coupled in that way that constructive
interference occurs along one axis, the intensity is lower for off-axis viewing
angles. The spatial angle of constructive interference shrinks to a fraction of
$4\pi$ when the length scale of the emission region is larger than the
wavelength of the radiation. This leads to an amplification of the received
radiation in addition to the relativistic beaming caused by the relativistic
radial outflow which is thought to be important for the radio emission of
pulsars. The effect will be calculated by numerical methods and can be
approximated by a simple analytic expression.
