Passive corner reflectors and active transponders are often used as man-made reference targets in Synthetic Aperture Radar (SAR) radiometric calibration, With the emergence of new radar systems and the increasing demand for greater accuracy, wide-band and wide-beam radars challenge the hypothesis that the Radar Cross Section (RCS) of reference targets is constant. In this study, the FEKO electromagnetic simulation software is used to obtain the change curve of the target RCS as a function of frequency and aspect angle while incorporating high-resolution point-target SAR simulation, and quantitatively analyzing the effect of the modulation effect on SAR images. The simulation results suggest that the abovementioned factors affect the SAR calibration by more than 0.2 dB within a fractional bandwidth greater than 10% or azimuth beam width of more than 20°, which must be corrected in the data processing.