该文从能量守恒观点出发，讨论了副面为椭圆的环焦天线的口径场分布，并导出了计算其方向图的简单表达式。
The aperture field distribution of the ring focus antenna is reviewed in view of the energy conservation law, and the simple formula for calculating its radiation pattern is deduced.
还指出仅当柱面或平面光栅时，才能形成二阶子午无离焦平场和弧矢无象散圆场谱面。
It is also shown that only when the gratings are cylinder or plane ones, the second order sagittal anastigmatic circular field and meridional non defocus flat field spectral images can be formed.
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