Abstract: A zone plate for focusing microwave energy is provided comprising a plurality of reflective portions corresponding to zones of the zone plate, each reflective portion reflecting energy .lambda./P out of phase with respect to adjacent reflective portions, where .lambda. is the wavelength of the energy. The reflective portions are positioned in P parallel planes mounted on low dielectric loss sheets and separated by a distance of .lambda./2P such that energy reflected from the reflective portions constructively interfere at a focus of the zone plate.

Abstract: Antenna apparatus has two laterally spaced waveguide horns with apertures covered by layers of gyrotropic ferrite material. The layers are angled to present opposite angles of incidence to radiation from a common distant source. Electromagnets produce magnetic fields in and parallel with the ferrite layers. The relative phase or amplitude of energy received on the horns is compared to indicate the direction of the source.

Abstract: A directionally sensitive receiving antenna, particularly for microwave radiation, utilizes the change in impedance, as a function of the angle between the energy vector of incident radiation on a gyrotropic medium, e.g. a ferrite material, and a magnetic field passing through the medium, enabling a highly directional antenna of small physical dimensions to be constructed.