An LFM-Based Semiblind Synchronization Method for Bistatic Radar Imaging

Bistatic radar provides an additional degree of freedom in the observing geometry for imaging by using a spatially separated transmitter and receiver. This capability allows the capture of scattering phenomena at various bistatic sensing angles, which helps to interpret the physical characteristics of a target or scene for remote sensing and radar applications. A crucial problem associated with bistatic radar is the synchronization of time and frequency between the transmitter and receiver for coherent image formation. In this article, a model-based method of synchronization, called semiblind synchronization, is introduced for maintaining the phase coherence of a bistatic radar system for range-Doppler processing. Specifically, semiblind synchronization refers to bistatic synchronization where the direct path is not available or where the global positioning system signal is not accurate enough, and where prior knowledge of the transmit waveform and target location are exploited during a coherent processing interval. The method focuses on error estimation and compensation based on understanding the impact of synchronization errors on the received signals. After detailing our system model and semiblind synchronization method, we conduct a simulation study for assessing the effectiveness of our method by first introducing a variety of synchronization errors, including chirp rate mismatch, and time and frequency offsets. Scattering responses from a point target are simulated, and high-range resolution profiles and range-Doppler images are formed to validate the proposed method. The simulation results demonstrate that a linear frequency modulation waveform enables us to estimate and compensate the synchronization errors considered in this article and improve the overall quality of the bistatic range-Doppler image. Our synchronization technique has potentially broad applicability in emerging remote sensing applications using bistatic radar systems.