In recent years, the influence of atmospheric irregularities on electronic systems has been recognized. How these irregularities affect electronic systems is related to the propagation environment, the scales of the irregularity, and parameters of the equipment. The phase deviation caused by the atmosphere is important to the interferometer. However, there are some filter effects, namely antenna aperture filter, Fresnel filter, and baseline filter, which must be considered. The first two filter out the effects of small scale irregularities, and the last one filters out larger ones.