A frequency synchronization scheme for time varying Doppler-shift compensation using the direct return signal

In this paper, a novel frequency synchronization scheme between platforms for a bistatic SAR is described. The proposed scheme uses the direct return signal to compensate a time varying Doppler-shift. The synchronization is established by using a PLL technique. And in a PFD of the PLL, the Doppler-shift of a reference signal for the PLL is canceled out by the Doppler-shift of the direct return signal. A detail analysis of the synchronization error for the proposed scheme is presented. Experimental results show that the proposed scheme achieves stable frequency synchronization between the platforms under the time varying Doppler-shift. And theoretical analysis and experimental results indicate that the synchronization error of 3.3×10−12 can be achieved in the assumed condition. This synchronization error is enough to satisfy the requirements for bistatic SARs.