Optimum primary radiator tilt angle of a shaped offset dual reflector antenna

Abstract

AbstractWhen we shape reflector surfaces of an offset dual reflector antenna for a given desired aperture distribution, we create a phenomenon in which the direction of the reflected ray by the shaped surfaces and an assumed direction of radiation by geometric optics do not coincide. Hence, the characteristics of cross‐polarized waves are degraded. If we shape the surfaces at a tilt angle of the main dish with respect to the direction of the main radiation pattern, we found that the directional errors become extremely small between the direction of the actually reflected ray and that of the assumed direction of radiation by geometric optics for an optimum tilt angle. At this tilt angle, we can shape the reflector surfaces satisfying almost all of the conditions imposed by geometric optics. When we shape the surfaces at the optimum tilt angle, we obtain continuous surfaces which generate a desired axisymmetric aperture distribution along the radial direction. We can design an offset dual reflector antenna with low sidelobes and favorable characteristics for cross‐polarized waves.Based on this theory, we built an experimental offset Gregorian‐type antenna with aperture diameter of about 50 λ. Measured results revealed excellent characteristics for cross‐polarized waves and those for sidelobes. Thus, we confirmed the validity of the theory of shaping reflector surfaces.