A Multibeam Cassegrain Antenna

This paper deals with generation of a multibeam pattern for three-dimensional radar surveillance by a stacked feed horn system installed in a Cassegrain antenna. Although its effective f/D-ratio is relatively high compared with the corresponding one of the primarily feed paraboloid, lateral displacement of feed horns in the focal plane results in strong pattern distortion caused by phase errors in the aperture plane. Investigations show that by means of an additional axial defocusing the quadratic term of these phase errors can be compensated improving the pattern distinctly, whereas the so-called Coma side lobe remains nearly unaffected. Basing on these results a feed horn system fulfilling special requirements was optimized and constructed. The obtained multibeam pattern of the Cassegrain antenna for the receiving case and the sectoral pattern for the transmitting case are shown.