空间外差光谱仪采用窄带滤光片限制仪器光谱范围，避免光谱混叠。滤光片透过率曲线随入射光角度的变化导致准直系统出射光场呈现随波长变化的非均匀现象。对光场非均匀性机理进行理论推导，证实滤光片调制作用造成复原光谱中卷积了与波长相关的调制函数，导致单色光光谱半峰全宽随波长变化。根据理论公式并结合实验室空间外差光谱仪参数进行了仿真分析，表明光场存在短波下凹和长波上凸的滤光片调制效应。开展了实验室单色光扫描实验，实验测量结果与理论分析和仿真结果一致。提出了一种包络线拟合校正方法，仪器线型函数半峰全宽变化量由校正前的16.7%下降为0.2%，有效去除了滤光片调制函数对仪器线型函数的影响。

The narrow band filter is used in spatial heterodyne spectrometers to limit the spectral range of the instrument and to avoid spectral overlapping. Due to the change of the filter transmittance with incidence angles, the emergent optical field from the collimating system is non-uniform at different wavelengths. The optical field non-uniformity mechanism is deducted theoretically, proving that modulation of filter causes convolution with a wavelength-related modulation function in restoration spectra and results in variation in full width at half maximum (FWHM) of monochromatic spectrum with wavelength. A simulation is carried out based on the theoretical formulas and the spatial heterodyne spectrometer parameters in laboratory, indicating that there exists influence of filter modulation that appears in concavity at shorter wavelength and convexity at longer wavelength. Monochromatic scanning experiments are performed in laboratory, and the measurement results are consistent with those of theoretical analysis and simulation. An enveloping line fitting correction method is proposed. The variation in FWHM of the instrument line function decreases from 16.7% to 0.2% after correction, suggesting that the influence of modulation function of filter on restored spectra is eliminated effectively.