A new dielectric grating antenna is proposed in this paper. The proposed all-silicon antenna consists of a rectangular dielectric waveguide with rectangular gratings on its both sides. This type of grating can be fabricated with low cost single print deep reactive-ion-etching process. The radiation mechanism in the proposed structure, is based on the power leakage of the order -1 space harmonic (Floquet's mode). The proposed optimized 94GHz antenna is well-matched over a more than 10% bandwidth with a frequency scanning ability up to 25 o (1dB variations in the gain).