Evaluation of caustics for parabolic reflector antennas through focal region ray tracings

In the case of designing Malaysia coverage contour beams by combining multiple beams, the relation between antenna beam direction and feed position becomes very important. This relation is known as the Beam Deviation Factor (BDF). Previously, an equation for the BDF was derived from an aperture phase distribution of a parabolic reflector antenna for feed displacements in the perpendicular plane to the antenna axis. Therefore, the equation gave information for one dimensional feed displacement. In this paper, ray tracings are performed in focal region of a parabolic reflector antenna for incident plane waves. The best feed positions are shown by caustics, which are the concentrated points of all rays. A set of caustic points form a line called locus of caustics. Based on the locus of caustics, the best feed positions are numerically clarified in two dimensional displacements.