Abstract
Rapid scanning using a paraboloid antenna is unsatisfactory; rapid movement of the antenna is mechanically impractical, while motion of the feed near the focus requires long focal length for good optical results. Another attack on the problem is to place the feed between parallel plates which produce a line source near a bifocal reflector. The energy flows along the geodesics of the mean surface between the parallel plates; the problem of shaping the plates so that a circular feed motion produces an oscillating beam at the line source becomes a problem in differential geometry and the calculus of variations. If the mean surface is assumed to consist of two developable surfaces joined along part of their boundaries, the unique solution of the optical problem is a circular disk along the edge of which the feed moves, joined to a section of a 60° cone which is straightened out at the large end to obtain a straight line source. This is the RCA solution of the problem. If the surface is assumed to consist of a surface of revolution which provides a feed circle, and attached to it a circular disk a diameter of which is the aperture, under certain natural restrictions no exact solution of the optical problem is possible, but several approximate solutions exist. Dielectric introduced between the plates of such a surface of revolution scanner effects a great improvement in the optics.
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