介绍了环面形稀疏孔径的结构,根据光瞳函数推导出其调制传递函数(MTF)表达式。利用Matlab软件模拟了环面形稀疏孔径在不同内外径比值e下的MTF；应用Zemax光学设计软件设计环面形稀疏孔径结构实例，分析其MTF特性并与理论模拟结果进行了比较；以标准鉴别率板为目标物体，对环面形稀疏孔径进行成像模拟，评价其成像性能，并利用阶数连续可调的分数阶微分算子增强图像。结果表明：环面形稀疏孔径调制传递函数的截止频率取决于外径的大小；随着e值的增大，MTF曲线在低频区域变得更加陡峭，且成像图像峰值信噪比逐渐减小；利用分数阶微分算子对图像进行增强，图像在细节得到强化的同时更好地保留轮廓信息。

The configuration of torus sparse aperture is introduced, and its modulation transfer function (MTF) is derived from its pupil function. MTF is simulated by Matlab software under different internal and external diameter ratios of torus sparse aperture; an example of torus sparse aperture is designed by Zemax software, from which the MTF is obtained and compared with the above simulation results; the imaging capability of torus sparse aperture is evaluated using the standard discrimination plate as the target object. The results show that the cut-off frequency of torus sparse aperture depends on the external diameter, and the MTF curves become steeper in low frequency area as the internal and external diameter ratio e increases. Imaging results also reveal that images′ peak signal-to-noise ratio (PSNR) decreases when the ratio e increases, and images′ details are enhanced with their contour information being kept in a better way when the fractional differential operator is utilized to enhance the image quality.