Wide-scanning multi-layer hemisphere lens antenna for Ka band

Abstract

Spherical lens antennas can produce multiple beams from multiple feeds, and these may be scanned to any angle. While an electrically large, uniform dielectric sphere offers mediocre aperture efficiency, this can be usefully increased by varying the dielectric constant with radius, as in the Luneburg lens. A continuous radial variation is difficult to achieve in practice and so a series of concentric shells is often preferred. A useful variant is that of the hemisphere lens used with a ground plane: this offers a relatively low-profile solution which is advantageous for a vehicle-mounted scanning antenna. A theory for the hemisphere lens radiation pattern is developed where this is described as the superposition of two spherical lens patterns i.e. that of the real and virtual sources. Measured radiation patterns of such lens antennas are reported which validate this theory. A prototype lens antenna is then reported which uses only two layers of dielectric material, which presents significant fabrication cost savings compared to a traditional Luneburg antenna. This 236 mm diameter lens offers 35.1 dBi of gain at 28 GHz (68% aperture efficiency) while scanning over a 150° solid angle.