A Novel Phase Synchronization Method for Spaceborne Multistatic SAR

The spaceborne multistatic synthetic aperture radar (SAR) system offers a flexible baseline that provides more observation angles and higher interferometry accuracy. However, any phase deviation among the independent oscillators in the spaceborne multistatic SAR system can cause a residual modulation of the echoes. Therefore, accurate phase synchronization is crucial for the system. The pulsed alternate synchronization scheme accurately extracts phase errors between different platforms, as verified in the TanDEM-X mission. Furthermore, an advanced noninterrupted pulsed alternate scheme uses the time interval of transmitting sequence to realize phase synchronization without interrupting the normal operation of the radar, which is verified in the LuTan-1 mission. However, with the increasing number of spaceborne multistatic SAR platforms, the time interval of the system may not be sufficient to support noninterrupted phase synchronization. To this end, this article proposes a novel phase synchronization method to improve the efficiency of phase synchronization for spaceborne multistatic SAR systems. First, a model for phase synchronization is built based on the pulsed alternate synchronization scheme, and the constraint between phase synchronization accuracy and waveform properties is analyzed in detail. Second, a quasi-orthogonal waveform optimization method, which can realize the rapid generation of phase synchronization waveform with better correlation properties, is introduced to improve the accuracy of phase synchronization. Third, to further reduce cross correlation energy between waveforms, we introduce generalized short-term shift-orthogonal (STSO) waveforms for phase synchronization. This waveform can achieve local orthogonality with a known baseline, improving the accuracy of phase synchronization greatly. Finally, the proposed method is verified through detailed simulations and ground experiments.