Line feeds for paraboloids

As a feed for a paraboloid, an endfire-line source facilitates polarisation diversity while having beamshaping potential for high efficiency. The geometrical limitations on the use of an endfire-line source as a feed for a Cassegrain aerial are examined and found to be no more stringent than those on the use of the Cassegrain system itself. In a Cassegrain aerial, the hyperboloid is usually in the near field of the feed. The focusing of a line feed to remove the resulting phase error is discussed. The aperture blocking by a line feed is also discussed, and is found to be less than half that of a horn feed, giving easier vertex matching.