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给定一个抛物反射面,将馈源置于焦点并不一定就获得最大的方向性.根据馈源的性质,馈源向着或离开反射面作轴向位移时可以获得最大的方向性.对于低一锥削馈源,位移应向着反射面,这个结果类似于称为焦点移动的光学现象.我们发现这一正的位移主要取决于反射面的菲涅尔数.对于高锥削馈源,位移应离开反射面.当反射面电尺寸小时,这种负位移就很有效.利用漏失、孔径照射效率和相位异步概念,提出一种统一的观点同时解释正位移和负位移.对于口径边缘锥削最佳的系统,不可能有焦点位移.
Given a parabolic reflector, it is not always possible to get the maximum directivity when the feed is in focus. Depending on the nature of the feed, the maximum directivity can be obtained when the feed is displaced axially towards or away from the reflector A taper feed, with displacement towards the reflective surface, is similar to the optical phenomenon known as focal shift and we found that this positive displacement mainly depends on the Fresnel number of the reflective surface.For high taper feeds, the displacement Should leave the reflecting surface.When the size of the reflecting surface is small, this negative displacement is very effective.Using the concept of leakage, aperture irradiation efficiency and phase asynchrony, a unified viewpoint is proposed to explain both positive and negative displacements.For the edge taper The best system, there can be no focus shift.