Study Of ISAR Imaging Algorithm For Small Targets With Space Rapid Maneuver

Inverse synthetic aperture radar(ISAR)imaging for long range maneuvering small/stealth target plays an important role in the field of defense space target surveillance.For the space small/stealth targets imaging,due to the target's small size,stealth feature,and the far distance between the maneuvering target and the radar platform,the received echo data has a low signal-to-noise ratio(SNR)and time-varying azimuth Doppler frequency,which make the Fourier transform based conventional range-Doppler algorithm is impossible to generate a well-focused ISAR image.Therefore,in recent years,how to obtain well-focused high resolution ISAR images for maneuvering target in low SNR environment has become a research hot and difficult point.Furthermore,the dihedral or trihedral components of the imaging target or the phenomena of range cell migration caused by the target's complex motion will result in the time-varying amplitude of the received echo signal,which bring a novel challenge for ISAR imaging algorithm design further.This paper focuses on the above problems,the main research contents and innovation points are as follows:(1)Due to the mutual restriction between the cross-terms suppression and the high time-frequency resolution in the traditional time-frequency analysis method,which results in the fact that the a clear high resolution ISAR image for maneuvering target is difficult to obtained using the time-frequency analysis based imaging algorithm.In this paper,a novel ISAR imaging algorithm for maneuvering target based on synchrosqueezing transformation(SST)is proposed.First,the received signal in a range bin can be characterized by a multicomponent polynomial phase signal(PPS)after translational compensation.The SST is a promising tool to analyze the multicomponent PPS signal since it provides high-resolution time-frequency distribution(TFD)for multicomponent PPS,but no cross-terms.And then the high-resolution ISAR image for maneuvering target can be obtained by extract the slice along an azimuth time.Computer simulation results and real data results demonstrate the superior performance of the proposed method.(2)The existing parameter estimation methods can not accurately estimate the parameters of polynomial phase signals at low SNR condition.In this paper,to exploit the amplitude and phase information of the PPS signal simultaneously,a novel coherently integrated generalized cubic phase function(CIGCPF)and the cubic phase function(CICPF)is proposed to enhance output SNR,suppress the cross-terms and spurious peaks,which solve effectively the problem that the conventional parameter estimation methods are difficult to estimate parameters of the multi-component PPS signals in low SNR environment.Moreover,the non-uniform fast Fourier transform(NUFFT)is also adopted to reduce the computational complexity.Finally,a high resolution imaging algorithm for maneuvering target is also provided,and simulated resulted validate the effectiveness of the proposed method.(3)The dihedral or trihedral components of the imaging target or the phenomena of migration through resolution cell for the target's complex motion will result in the fact that the available constant amplitude QFM signal model can't accurately describe the time-varying amplitude characteristics of the radar echo signal.In this paper,the received signal in a range bin is characterized as multicomponent amplitude modulated--quadratic frequency modulated(AM-QFM)signal with time-varying amplitude after translational compensation,and a novel coherently integrated cubic phase function(CICPF)is proposed to estimate the parameters of multi-component AM-QFM signal in the low SNR environment.Compared with the existing ISAR imaging methods based on the constant amplitude signal model,the well-focused ISAR image can be obtained by the proposed method.Finally,simulated results demonstrate the effectiveness of the proposed algorithm in this paper.