The information of the shape,size and structure of non-cooperative targets can be obtained by the inverse synthetic aperture radar(ISAR)imaging technique,therefore,in target classification and recognition,ISAR imaging plays an important role.Maneuvering targets and targets with complex motions are common non-cooperative targets,the model of multi-component polynomial phase signals can be used to characterize the echo of these targets after motion compensation.ISAR image can be obtained after applying signal processing methods to the multi-component polynomial phase signals,and the quality of the ISAR image lies on the signal processing methods.In order to improve the quality of the ISAR image of maneuvering targets and targets with complex motions,some researches have been done in this dissertation,the main work is summarized as follows:1.The ISAR imaging principles of maneuvering targets and targets with complex motions are introduced.According to the movement characteristics,after motion compensation,the echo of maneuvering targets can be described as the linear frequency modulated(LFM)signal,and the echo of targets with complex motions can be described as the cubic phase signal(CPS).Parameter estimation of the LFM signal and the CPS is an important procedure in ISAR imaging,in this dissertation,the presented parameter estimation algorithms are summarized and classified,and some classic algorithms are introduced in detail.2.For maneuvering targets,an ISAR imaging technique based on the centroid frequency-chirp rate distribution(CFCRD)is proposed.CFCRD is a new parameter estimation algorithm for the LFM signal,the fast Fourier transform(FFT)and the modified scaled Fourier transform(MSFT)are utilized to complete the energy accumulation in the CFCRD.The advantages of CFCRD are(1)spectrum aliasing can be avoided due to the introduction of the zoom factor in the MSFT;(2)CFCRD can acquire higher anti-noise performance due to the usage of the previously processed data.Compared to other ISAR imaging algorithms for maneuvering target,the ISAR imaging algorithm based on the CFCRD is demonstrated to be more practical with performance analyses,and simulations using the synthetic and the real radar date.3.For targets with complex motions,an ISAR imaging algorithm based on the modified Lv's distribution(MLVD)is proposed.A new parametric symmetric self-correlation function is defined in the MLVD,and the keystone transform is used to remove the linear coupling caused by the parametric symmetric self-correlation function for the echo.Thereafter,along the slow time axis,the FFT operation is used to complete the energy accumulation.The keystone transform can be implemented by the FFT operation and the inverse fast Fourier transform(IFFT)operation based on the chirp-z transform,therefore,the FFT operation,the IFFT operation,and the complex multiplication can complete the implementation of the MLVD.Due to the utilization of the new parametric symmetric self-correlation function,the MLVD can acquire higher anti-noise performance compared to other algorithms.After analyses and verification of the MLVD,the ISAR imaging algorithm based on the MLVD is proposed,and the effectiveness of the ISAR imaging algorithm is validated with the synthetic data and the real radar data.4.For targets with complex motions,the ISAR imaging algorithms based on the modified chirp rate-quadratic chirp rate distribution(M-CRQCRD)and the integrated modified chirp rate-quadratic chirp rate(IM-CRQCRD),and a cross-range scaling algorithm of the ISAR image are proposed.In M-CRQCRD,a new parametric symmetric self-correlation function is defined to improve the anti-noise performance.The nonlinear coupling caused by the parametric symmetric self-correlation function for the echo can be removed by the keystone transform,thereafter,along the slow time axis,the non-uniform fast Fourier transform(NUFFT)operation is used to complete the energy accumulation.Therefore,the implementation of the M-CRQCRD only needs the FFT operation,the IFFT operation and the NUFFT operation,and the searching procedure due to the non-uniformly spaced signal is avoided.Through noncoherent integrations of the M-CRQCRD which use different constant time delays,the anti-noise performance of the IM-CRQCRD is further improved.After analyses and verification of these two algorithms,the corresponding ISAR imaging algorithms are proposed,and the synthetic and the real radar data are utilized to validate the effectiveness of these two ISAR imaging algorithms.In addition,for better target recognition,a cross-range scaling algorithm of the ISAR image for the target with complex motions is presented.In this algorithm,the estimate of the rotational velocity is obtained by using the relation between the parameters of the CPS and the rotational velocity,thereafter,the ISAR image is rescaled from the range-Doppler domain to the range-cross-range domain,and the real size of the target can be get.The feasibility of the proposed algorithm is verified through simulations. |