Improved element pattern for the line feeds of the spherical reflector antenna in Arecibo

The line feeds of the spherical reflector antenna in Arecibo are considered. A model for the element pattern is presented and used to give a better explanation of the central dip in the radiation pattern of the line feed than that given before. The model includes the effect of the fins between the elements by considering the line feed to be a circularly corrugated cylinder. Such a corrugated cylinder has, according to recent results, a soft outer surface at which the electric field vanishes.<
>