According to the characteristic that the bandwidth of spaceborne SAR(Synthetic Aperture Radar) is generally quite wide

a method called "Sub-band Double Carrier Frequency Conjugated Processing" is presented.The approach can decrease the equivalent central frequency of the synthetic signal and remove the Doppler ambiguity.Consequently

Keystone transform can be used to correct the linear range migration of the fast moving target with low input SNR.After the target range curvature is corrected

time-frequency analysis can be used to implement low resolution imaging and targets detecting.The radial velocities of targets can be obtained from targets detection

and high resolution imaging process can be completed to each moving target.The simulation results show the effectiveness of the new method.