Quantum cascade lasers operating in the THz region are of great potential interest as local oscillators for THz heterodyne detection, and more general, as sources for imaging purposes. To assess the applicability of this new source beam profile, measurements on 'metal-metal' cavity QCL's have been performed. Contrary to earlier waveguide based simulations, the beam patterns show strong angular intensity oscillations, depending on the length of the laser cavity and the emission wavelength. The experimental results have been compared with a simple theoretical model.