This comes from the fact that surface current distribution (30) is calculated from I& only. So the far-field calculations correspond to (19). In fact, there is a constant proportionality between f,, F,, and.&., F, from (19) and (31). As D/I increases, the angle 0, which sees the main lobe and first few sidelobes, gets smaller so the term (1cos 0) approaches zero yielding zero far-field cross polarization provided polarization purity is achieved at the aperture plane. CONCLUSIONS All these considerations lead us to the conclusion that the cross polarization performance of reflector antenna system largely depends on the feed system and I / D ratio. For this reason, superior performance of Cassegrainian or front-fed paraboloids with respect to polarization purity is closely related to the feed design. Thus this paper puts an end to the controversy recently arisen ([7]-[9]) about the immunity of these two types of antenna systems against depolarization effects. A detailed treatment may be required to see to what extent other factors may influence the cross polarization performance of reflector antennas.
Absmct-New aigorithms are presented for the solution of optimum tolerance assignment problems. The problems considered are dermed mathematicaiiy as a worst-case problem (WCP), a fiied tolerance problem (FTP), and a variable tolerance problem (VTP). The basic optimization problem without tolerances is denoted the zero tolerance problem (ZTP). For solution of the WCP we suggest application of interval arithmetic and also alternative methods. For solution of the FlT an aigorithm is suggested which is conceptually simiiar to algorithms previously developed by the authors for the ZTP. Finally, the VTP is solved by a double-iterative algorithm in which the inner iteration is performed by the FTP-algorithm. The appiication of the algorithm is demonstrated by means of relatively simple numericai examples. Basic properties, such as convergence properties, are displayed based on the examples.
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