理论上提出了平顶正弦相位板星冕仪, 该星冕仪可作为正弦相位板星冕仪和六平台相位板星冕仪的推广形式。平顶正弦相位板具有角向的双周期结构, 每个周期中都包含两个平顶的半正弦区域和一个平坦区域。解析地推导了该相位板的宽带工作条件。在这个宽带工作条件的一端, 这个相位板可以退化为正弦相位板; 在另一端, 这个相位板可以退化为六平台相位板。数值计算结果表明, 平顶正弦相位板星冕仪与这两种特例情况一样, 具有良好的消色差能力。

A flat-top sinusoidal phase mask coronagraph is theoretically studied, it is the generalized form of the sinusoidal phase mask coronagraph and the six-level phase mask coronagraph. This kind of phase mask is a double-periodic phase mask with both the flat-top sinusoidal and the constant parts in the azimuthal phase in each period. The wideband working condition for this kind of phase mask is analytically presented. On one end, the wideband working condition reduces to that of a sinusoidal phase mask. And on the other end, it reduces to that of a six-level phase mask. Just like its two special examples, the numerical calculation shows the flat-top sinusoidal phase mask coronagraph generally has the advantage of achromatism.