An angular beaming model for constituents of pulsar emission is examined. It is proposed that both subpulses and micropulses are generated by the same narrow-band emission mechanism. Micropulses correspond to a thin plasma column flowing along dipolar magnetic field lines. The width of the micropulses is determined by relativistic beaming. It is shown that if the mapping radii r (196.3 MHz) and r (318 MHz) differ by less than 20 stellar radii R, then the micropulses in PSR 1133 + 16 should be simultaneous at the source between 318 and 196.3 MHz, as observed.