Double-slot antennas on extended hemispherical and ellipticalsilicon dielectric lenses

Far-field patterns and Gaussian-beam coupling efficiencies are investigated for a double-slot antenna placed on hemispherical lenses with varying extension lengths. The radiation patterns of a double-slot antenna on a silicon dielectric lens are computed using ray-tracing inside the dielectric lens and electric and magnetic field integration on the spherical dielectric surface. The measured radiation patterns at 246 GHz and Gaussian-beam coupling efficiencies show good agreement with theory. The theoretical results are presented in terms of extension-length/radius and radius/λ, and therefore result in universal design curves for silicon lenses of different diameters and at different frequencies. The theoretical and experimental results indicate that for single units, there exists a wide range of extension lengths which result in high Gaussian-coupling efficiencies (50-60%) to moderately high f 's. These Gaussian-coupling efficiencies can be increased to 80-90°% with the use of a λ_m/4 matching-cap layer. For imaging array applications with high packing densities, an extension-length/radius of 0.38 to 0.39 (depending on frequency) will result in peak directivity and a corresponding Gaussian-coupling efficiency 15-20% lower than for single units