A supplement and an expansion of authers previeous work (1990) are presented. The improved perturbation method is used for analyzing the radiation characteristics of the millimeterwave dielectric grating antennas with various groove profiles. A comparison between the results given and those obtained by the rigorous calculations shows that the present analysis yields as highly accurate results as the rigorous method but the calculation procedure is tremendously simplified. Based on this, the effects of groove profiles on the performances of the grating antennas are systemetically studied. The curves given in this paper may be used as reference for designing the dielectric grating antennas.