A numerical analysis of a generalized dielectric waveguide mirror of arbitrary structure angle is presented. A plane wave expansion technique is used to calculate output angle, power transmission, interwaveguide and intrawaveguide coupling, far-field emission profile, and losses of the waveguide mirror. In order to evaluate the effect of divergence, two methods are used and the results indicate that the effect is minimal. Furthermore, the introduction of a tilt in the mirror surface is examined, and reveals a reduction in the interwaveguide coupling as the tilt is increased. However, this coupling remains symmetric in tilt despite the asymmetry of the geometry due to the tilt. Results of the output angle and the FWHM of the emission profile are compared to experimental values obtained for a semiconductor triangular ring laser.