A NEW APPROACH FOR SHAPING OF DUAL-REFLECTOR ANTENNAS.

摘要

A new approach is studied for the shaping of two-dimensional dual-reflector antenna systems to generate a prescribed distribution with uniform phase at the aperture of the second reflector. This method is based on the geometrical nature of Cassegrain and Gregorian dual-reflector antennas. The method of synthesis satisfies the principles of geometrical optics which are the foundations of dual-reflector designs. Instead of setting up differential equations or heuristically designing the subreflector, a set of algebraic equations are formulated and solved numerically to obtain the desired surfaces. The caustics of the reflected rays from the subreflector can be obtained and examined. Several examples of two-dimensional dual-reflector shaping are shown to validate this study. Geometrical optics and physical optics are used to calculate the scattered fields from the reflectors.;A blended rolled edge attachment to the shaped main reflector for compact range applications is also investigated. The addition of rolled edges to the main reflector reduces the edge diffracted field which causes ripple in the aperture field. A method for correcting false end-point contributions which result from the use of physical optics are reviewed. Several examples are given to illustrate the improvement achieved in the aperture field by adding the blended rolled edge terminations. Corrections for the end-point contributions are included in these examples in order to obtain the true scattered fields from the reflectors. The same method of synthesis is also used for shaping of a three-dimensional circularly symmetric dual-reflector antenna. This case is also verified by examples.