A toroidal microwave reflector

Many applications require reflectors capable of providing wide angle scanning of a pencil beam in a plane, and it has been demonstrated that the torus type is superior to other known reflectors for this purpose. The parabolic torus, in particular, is formed by revolving a parabolic generating curve about an axis parallel to the latus rectum. Scanning is obtained by rotating a feed on the arc of a circle centered on this axis so that, due to symmetry, radiation patterns are identical for all feed positions. However, the parabolic torus has inherent phase errors which limit the useful reflector area. This paper discusses a reflector derived by assuming a toroidal surface and numerically calculating the generating curve to provide a balance of phase errors over the illuminated area. The generating curve so determined was found to be an ellipse. Accordingly, this new reflector is referred to as an elliptical torus. In magnitude, phase errors from the elliptical torus are approximately one-half those from the parabolic torus. Radiation patterns from experimental reflectors show that for very large apertures in terms of wavelengths, the elliptical torus gives a narrower beam than a parabolic torus with the same aperture size and same f/D ratio.