Abstract: A cavity backed crossed slot antenna wherein the cavity depth d is less than one eighth of the operating wavelength .lambda. at the lowest frequency of operation, the major dimension a of the cavity in the plane of the slots is less than one half of the wavelength .lambda. at the lowest operating frequency, and the slots are excited by four symmetrically located capacitive coupled feed probes.

Abstract: An antenna system which has omnidirectional coverage in azimuth and sectoral coverage in elevation. A main reflector including a reflecting surface has polar symmetry about the Z-axis. It also has a cross section in any plane containing the Z-axis which satisfies the laws of power conservation and reflection. It is determined by the desired far-field pattern and the microwave feed pattern (for example TM.sub.01) employed. Single or dual reflector systems are described. Using the system on "receive" with multiple "feeds", full azimuthal direction finding of incident radiation can be achieved.

Abstract: A microwave apparatus comprises a waveguide section including a stepped septum. The septum is positioned so as to divide the waveguide into two channels. The steps comprise a plurality of first steps which advance progressively in one direction and at least one second step, or the equivalent, which follows the first steps and which returns in an opposite direction. The invention is intended to enable the production of a circularly polarized microwave signal without requiring the use of phase adjustment techniques.