The present invention relates in general to radiating elliptically polarized energy and more particularly concerns novel apparatus and techniques for radiating circularly polarized energy at relatively high power levels over a relatively broad frequency range from a horn with controlled directivity and a relatively high degree of circularity over the frequency range. A horn according to the invention is relatively compact, relatively easy to fabricate and provides good electrical and mechanical performance with relatively little maintenance.
Maintaining good circularity for highly asymmetrical beamwidth horns has been difficult. Among the prior art approaches are using arrays of horns, sectoral horns with meanderline transmission-type polarizers, constricted-aperture horns filled with dielectric to prevent cutoff and various rod-like parasitic devices to broaden the beam width in the aximuth plane.
The prior art approaches have a number of disadvantages. Those using parasitic devices have a tendency to work only over a relatively narrow frequency range. These using meanderlines have been inherently limited to relatively low power levels. Sectoral horns and arrays have been of large physical size. Those with constricted apertures present problems of maintaining impedance match, and those with dielectrics in the constricted apertures are relatively heavy.
Accordingly, it is an important object of this invention to provide an improved radiator of circularly polarized energy over a relatively broad range of frequencies that overcomes one or more of the disadvantages enumerated above.
It is a further object of the invention to achieve the preceding object over at least an octave.
It is a further object of the invention to achieve one or more of the preceding objects while radiating relatively high power levels.
It is still a further object of the invention to achieve one or more of the preceding objects with relatively compact structure that is relatively lightweight.
It is a further object of the invention to achieve one or more of the preceding objects while maintaining a desired impedance match with relative ease.