Theoretical and Experimental Investigation of Gaussian Beam Transmission and Reflection by a Dielectric Slab at 110 GHz

Transmission and reflection properties of a Gaussian beam incident upon a dielectric slab are investigated by means the plane-wave spectrum method and compared with experimental results made at 110 GHz. The incident wave generated by a special circular horn antenna at 110 GHz is modeled as a two-dimensional Gaussian beam under the paraxial approximation and also as a simplified one-dimensional beam with a spreading factor. Measurement results are presented for the transmission and reflection of both the perpendicular and parallel polarizations. In particular, reflection measurements for a parallel-polarized beam incident at and near the Brewster angle are shown and compared to the theory. A small reflected two-lobe beam is observed even at the exact Brewster angle. Nonspecular phenomena in Gaussian beams are discussed and the relevance to a Brewster window for the output of a gyrotron is considered