A study of spherical reflectors as wide-angle scanning antennas

Abstract

A study is made of spherical reflectors for use as wide-angle scanning antennas. In order to keep the effects of spherical aberration within tolerable limits, the approach of using a restricted aperture is adopted. This approach is suitable for applications requiring very wide angles of scan. Experimental results show that the phase error over the illuminated aperture of a spherical reflector should not exceed one-sixteenth of a wavelength. This requirement determines the beamwidth of the primary source. A square-aperture horn with diagonal polarization is found to satisfy the requirements of a suitable feed for the reflector. Secondary patterns of a 10-foot-diameter hemispherical reflector illuminated by this horn at 11.2 kmc have a 3-db beamwidth of <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1.76\deg</tex> and a relative sidelobe level of about -20 db throughout a total useful angle of scan of <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">140\deg</tex> . The measured gain is 39.4 db, which is equivalent to the gain of a uniformly illuminated circular aperture of 31-inch diameter.