Radiation properties of parabolic torus reflector

General radiation-pattern formulas for a torus reflector antenna have been developed using physical optics. These expressions are valid at arbitrary feed locations not only within the primary focal arc but also for beam scanning with squinted feed horn illuminations. Numerical results were obtained at 22 GHz for an experimental 1.25 m*2.5 m torus reflector in both elevational beam scanning and extended azimuthal scanning outside the primary +or-15 degrees field of view. An elevation scanning range of 7 degrees showed only a 1 dB gain reduction. The 20 degrees azimuth beam (i.e. 5 degrees extended azimuth scanning) showed a 1.4 dB gain reduction. Comparison between calculated and measured patterns showed agreement in beamwidth and most pattern features. The discrepancy between calculated and measured sidelobe levels in the azimuthal plane is attributed to imperfection enhancement by the horizontal oversize of the reflector.>