信号光与本地光的夹角是影响探测器输出外差信号强度的主要因素。当夹角过大时，甚至不能检测到外差信号。通过分析提出，外差信号的振幅实际上是接收孔径透射率函数的傅里叶变换，以此为依据提出一种降低失配角对外差信号影响的方法，即在接收孔径处放置透射率分布满足一定函数形式的透过型元件，使其傅里叶频谱满足预定的要求，这种情况下两光束夹角增大时，探测器输出的外差信号强度能得到增强,从而降低了对探测系统瞄准精度的要求。

The angel between signal light and local light is an important factor to the heterodyne detection. When the angle is too large, one even cannot detect the heterodyne signal. It is proposed that the amplitude of heterodyne signal output by detection is just the Fourier transform of aperture transmittance function. Based on the theory, a method that can reduce the influence of spatial mismatch angle on heterodyne detection is proposed. Namely, if a component whose transmittance is a certain function is placed on the aperture surface and the Fourier transform of the function meets certain requirement, one can find that the amplitude of heterodyne signal may be enhanced when the angle between the two beams becomes large, which can reduce the requirement for pointing accuracy of detection system.