In this study, the beam broadening effect on Doppler spectrum was investigated with theoretical derivation and numerical simulation. It is found that vertical wind may cause a beam broadening spectrum not in exact Gaussian shape. Moreover, the azimuth angle variation of the beam broadening spectral width in the presence of vertical wind is more significant than that in the absence of the vertical wind. The widths of the beam broadening spectra for oblique beams pointing in the opposite directions are different. Further, wind shear effect on the azimuth anisotropy of the beam broadening spectral width is also studied in this article. In the context of three-dimensional wind field with vertical shear of horizontal wind, an analytic expression of the beam broadening spectral width is proposed. A comparison between the analytic expression and simulation result suggests that the expression is applicable in general.
