  In the Terahertz (THz) domain, we investigate both numerically and
experimentally the directional emission of whispering gallery mode resonators
that are perturbed by a small scatterer in the vicinity of the resonators rim.
We determine quality factor degradation, the modal structure and the emission
direction for various geometries. We find that scatterers do allow for
directional emission without destroying the resonator's quality factor. This
finding allows for new geometries and outcoupling scenarios for active
whispering gallery mode structures such as quantum cascade lasers and passive
resonators such as evanescent sensors. The experimental results agree well with
finite difference time domain simulations.
