| Two kinds of offset dual-reflector antennas, classical offset Cassegrain and Gregorian dual-reflector antenna, are mainly discussed in the thesis. Modified Jacobi polynomials are used to describe the surface of the reflector. And the physical optic (PO) method based on the surface current integration is employed as the research method. Then properties of beam scanning and array compensation based on the conjugate field matching (CFM) method are studied in detail. Finally, the real-coded genetic algorithm (RGA) is established to shape the dual-reflector, realizing the shape of the expected patterns.First of all, the characteristics of the radiation, focal region and beam scanning of the single parabolic reflector antenna are analyzed.Secondly, the dual surface current method is introduced. Then, the properties of the radiation, focal region and the beam scanning of the offset dual-reflector antennas are proposed, based on the analysis of the single parabolic reflector antenna. A single feed is replaced by a 19-elment cluster to illuminate the reflector and the excitations of them are obtained by CFM method, improving the scanning property remarkably.Finally, a set of orthogonal global expansion functions (modified Jacobi polynomials) are employed to describe the surface of the offset single parabolic reflector and the offset dual-reflector, respectively. By optimizing these coefficients, the surface of the reflector is shaped and the territories of China and Brazilian are well-covered by the contour beam patterns. The results of these two reflectors are compared. It concludes that the cross-polarization level is lower and the surface distortion is much smaller than the single-reflector for the dual-reflector antenna, thus possessing much better shaping capability. |
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