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Due to the advantages of flexible configuration, bistatic synthetic aperture radar (BiSAR) has the ability to effectively observe from various visual angles, such as forward view area and squint area, and has good anti-jamming characteristics. It can be applied to the surveillance of ship targets on the sea and is gradually gaining an increasing amount of attention. However, for ship targets with complex motions on the sea surface, such as maneuvering targets or ship targets under high sea conditions, the high-order Doppler frequency of the scattering points is always spatial variation (related to the spatial position of scattering points), which poses a considerable challenge for the imaging of maritime ship targets in BiSAR. To resolve this problem, a BiSAR maritime ship target imaging algorithm based on cubic phase time-scaled transformation is proposed in this paper. First, through pre-processing of echo such as Doppler prefiltering and keystone transform, the translation compensation of the BiSAR maritime ship target is completed, and the scattering point energy is corrected to within one range unit. Then, the azimuth signal is modeled as a multi-component cubic phase signal. Based on the proposed cubic phase time-scaled transformation, the Doppler centroid, frequency rate, and third-order frequency of scattering points are estimated. Eventually, the BiSAR imaging of maritime ship targets is realized. This algorithm has excellent noise immunity and low cross-terms. The simulation leads to the verification of the validity of the proposed algorithm. [ABSTRACT FROM AUTHOR]

Bistatic synthetic aperture radar (BiSAR) has received more and more attention because of its forward-looking imaging capability and configuration flexibility. For BiSAR moving target imaging (MTIm), its noncooperative motion leads to unknown range cell migration (RCM) and additional phase modulation. Consequently, MTIm in BiSAR faces two main challenges: 1) the unknown RCM correction and Doppler parameter estimation are tightly coupled and 2) the Doppler parameters of the extended moving target’s different scattering points are different, i.e., the Doppler parameters are spatially variant. To cope with these problems, an optimal polar format refocusing method for bistatic SAR MTIm is proposed. First, the main part of tight coupling and spatial variation effects caused by the BiSAR platforms is eliminated, while the moving target is 2-D defocused and shifted. Then, we analyze the characteristics of 2-D defocused and shifted of the moving target in BiSAR and give the analytical expressions. Basis this, a new bistatic polar format transformation is introduced, in which the degree of freedom of defocusing result is reduced from 2-D to only 1-D. After that, the parameter estimation and refocusing issues are transformed into a constrained optimization problem (COP), and differential evolution (DE) is applied to solve the COP and obtain the refocusing results. Finally, considering the spatial variation of the extended moving target, compensation processing is performed to relocate each scattering point. Numerical simulations verify the effectiveness of the proposed method. [ABSTRACT FROM AUTHOR]