| As an indispensable technology,radar imaging has been applied in many fields,especially on high-speed maneuvering platforms,which can enhance the ‘anti-access/area denial’capability and is a major strategic requirement for national security.In addition,radar imaging technology can also improve the long-distance detection,identification and positioning capabilities of high-speed maneuvering platforms for ground/sea targets.It is the core key technology that needs to be urgently developed to enhance national defense capabilities.However,when the high-speed maneuvering platform performs terminal dive,multi-directional guidance,long-range search and other situations to detect targets,its motion flight trajectory is generally a nonlinear curve trajectory with variable speed in space,resulting in serious two-dimensional coupling and high-order Phase space variation errors in radar echo signal,which leads to failure of traditional imaging processing methods.Therefore,under the guidance of the practical application background requirements of the high-speed maneuvering platform,this dissertation carries out innovative theoretical and application research on the difficult problem of high-speed maneuvering platform curved trajectory high quint SAR imaging.The specific research content mainly includes the following four parts:1.Aiming at the problem of nonlinear trajectory of high squint SAR imaging mounted on high-speed maneuvering platform,this dissertation first extracts and compensates the threedimensional trajectory disturbance component in the nonlinear trajectory imaging range model,and on this basis,proposes a high squint imaging algorithm based on high-order phase filtering in time domain.The range signal spectrum is analyzed and discussed by highorder Taylor approximation expansion,and the range migration correction is completed to realize the range focusing processing.In order to solve the problem of high-order spatial variation of azimuth phase,the phase adjustment factor is first introduced in the azimuth frequency domain,and then the high-order phase spatial variation filter function is introduced in the azimuth time domain.The first-order and second-order spatial variation of azimuth frequency modulation and the first-order spatial variation of cubic phase coefficient are used to realize azimuth unified compression and focusing.Finally,the experimental results of both simulation and real data verify the effectiveness of the proposed algorithm.2.For the problem of high squint SAR imaging mounted on high-speed maneuvering platform with curve trajectory,firstly,the squint range model with curved trajectory imaging is equivalently simplified into two items: the standard hyperbolic squint range model and the squint range model with acceleration,and on this basis,high squint SAR imaging algorithm based on interpolation resampling processing is proposed.By compressing and rotating the two-dimensional spectrum,the influence of the acceleration component on the spectrum broadening is eliminated.In order to facilitate the subsequent unified processing,the residual phase error introduced by the acceleration is compensated and corrected,and then the signal is resampled by unified interpolation to eliminate the azimuth space-varying characteristics,and then the two-dimensional signal is decoupled by extended Stolt interpolation.In order to avoid a large amount of zero padding in the azimuth,the image is focused in the range time domain azimuth wavenumber domain by spectral de-aliasing.Finally,the experimental results of both simulation and real data verify the effectiveness of the proposed algorithm.3.For the imaging problem of high squint SAR mounted on high-speed maneuvering platform with curve diving trajectory,an improved curved-dive slope-range imaging model was constructed,and the imaging parameters such as acceleration are uniformly and equivalently represented,which solve the problem of mismatch between traditional imaging model and echo signal,and on this basis,an imaging algorithm based on extended OmegaK is proposed.The maximum utilization of the two-dimensional spectrum is obtained by spectrum rotation,and then the high-order polynomial fitting method is used to linearize the spectrum,and on this basis,an improved Stolt interpolation mapping is proposed to complete the range signal processing.In order to realize sub-aperture imaging and avoid a large number of zero padding operations in azimuth,the image focus domain is selected in the range time domain and azimuth frequency domain by spectral unmixing;then high-order phase space variation correction functions are constructed in the azimuth time domain and frequency domain respectively to eliminate the space-variant error of the azimuth and phase,and realize the unified focus compression processing of the azimuth.Finally,the experimental results of both simulation and real data verify the effectiveness of the proposed algorithm.4.Aiming at the problem of high squint imaging mounted on high-speed maneuvering platform with arbitrary curve trajectory,the principle and key steps of the traditional FFBP imaging algorithm based on the straight trajectory are analyzed firstly,then it is improved by projecting and decomposing the arbitrary curve trajectory configuration and establishing a three-dimensional virtual coordinate system.At the same time,in order to improve the processing efficiency of the time-domain imaging algorithm,a fast time-domain BP imaging algorithm based on improved spectral compression is proposed.By constructing the ground trapezoidal coordinate system of any curve trajectory,the accurate two-dimensional spectrum expression of the imaging target is derived,and on this basis,the target spectrum is compressed and rotated to align,which greatly increases the number of points required for coherent image synthesis of each sub-aperture and improves the processing efficiency of the time-domain BP algorithm.Finally,the experimental results of both simulation and real data verify the effectiveness of the proposed algorithm. |
PDF Full Text Request