【作者】 刘峰；

【导师】 牟善祥；

【作者基本信息】 南京理工大学 ， 信息与通信工程， 2017， 博士

【摘要】 合成孔径雷达(SAR)在军事和民用领域的不同应用场景中有着广泛的需求。将同平台多天线技术与SAR相结合,为解决常规单天线SAR面临的高分辨率和宽测绘带互相制约的矛盾等实际问题提供了有效的途径。同平台多天线SAR相对于常规SAR具更多的系统自由度,结合数字波束形成(DBF)技术,利用多个发射波形的相关特性和等效阵列的波束特性能够提高SAR系统的性能。因其在高分辨率宽测绘带成像、动口标检测及抑制干扰等方面的显著优势,受到了国内外遥感领域和雷达成像领域的广泛关注,成为该领域研究的热点之一。论文以常规SAR成像技术为基础,针对高分辨率宽测绘带、动口标检测及大数据量等问题,以同平台多天线SAR成像理论与方法作为研究内容,分别研究了距离向多天线、方位向多天线、距离向和方位向联合多天线SAR成像模式,提出了基于互质阵列的MIMO SAR成像方法、基于分数阶傅里叶变换的非均匀采样DPCMAB成像方法以及基于压缩感知的MIMO SAR宽测绘带成像方法。论文主要工作和创新总结如下:1、研究了大斜视SAR成像算法。对斜视SAR的回波表达式进行了详细的推导和分析,提出了一种时域校正距离走动的大斜视扩展线性调频变标(ECS)成像算法。该算法在时域进行距离走动校正,利用等效的ECS成像算法进行成像处理。距离走动校正只需要简单的相位相加即可完成,流程简单,计算量适中。仿真结果验证了算法的可行性和有效性。2、在距离向多天线SAR成像模式下,提出了基于互质阵列的MIMO-Cop SAR成像方法。首先研究了基于线性调频脉冲信号的MIMO SAR波形设计,分析了基于线性调频脉冲信号的波形集,并推导了脉冲间调斜率不同时精确的模糊函数表达式;将Costas编码和线性调频信号相结合,设计了脉间Costas跳频脉内随机斜率线性调频(IPC-SCLFM)的波形集。然后将IPC-SCLFM波形应用于距离向多天线SAR成像,提出了一种基于互质接收阵列的MIMO-Cop SAR成像方法。给出了两种互质接收线阵结构,将DBF技术应用于回波信号,并利用简单的相乘处理,完成信号分离,很好地抑制了互相关电平,有效地减少了回波信号的数据量。最后进行了仿真实验,结果表明,成像效果性能良好,有效地抑制了噪声。同时MIMO-Cop SAR也适用于OFDM-LFM信号体制。3、在方位向多天线SAR成像模式下,提出了基于分数阶傅里叶变换(FrFT)的非均匀采样SAR成像方法。由于方位向多天线的尺寸误差、安装误差,以及平台的非匀速运动,回波在方位向会产生非均匀采样的问题。在多相位中心多波束(DPCMAB)SAR成像中,将非均匀采样点在分数阶Fourier变换域上重构能够得到原始信号均匀采样的分数阶频谱。回波数据距离压缩后进行方位向重构,获得重构后的数据再进行FrFT变换,得到动目标的参数估计,从而实现了对动目标成像,有效的解决了非均匀采样和动目标检测的问题。通过理论仿真验证了此方法的有效性。4、在距离向和方位向联合多天线成像模式下,提出了基于压缩感知的MIMO SAR宽测绘带成像方法。距离向接收天线采用稀布阵,给出了基于压缩感知的MIMO SAR的回波数学模型,回波信号进行等效发射DBF处理,提高了距离向分辨率,利用基于压缩感知的零点指向技术对距离模糊进行抑制。方位向采用DPCA技术对接收信号进行相位等效处理,提高了方位向分辨率,从而对目标进行二维成像。仿真结果表明,压缩感知技术有效地减少了稀布阵宽测绘带成像的数据量,验证了此方法的可行性和有效性。更多还原

【Abstract】 In order to meet the increasing application demand,synthetic aperture radar(SAR)has been widely used in military and civil area.The coherent multi-antenna technique has been applied to SAR.The novel developing imaging technology based on multi-antenna is able to simultaneously improve the performance of SAR imaging by utilizing multiple antennas both at transmission and reception.Multi-antenna SAR system can provide more degrees of’freedom than traditional SAR.With the digital beamforming(DBF)technique,it shows a distinct advantage in moving target detection,high resolution and wide swath,and interference suppression based on the correlation characteristics of multiple transmit waveforms and equivalent array beam.It is received great attentions in remote sensing and radar imaging,and becomes one of research hotspots.Based on traditional SAR imaging technique,for the problems such as high resolution and wide swath,moving target detection and large amount of data,this dissertation focuses on imaging theory and method of coherent multi-antenna SAR.The key researches include multiple input and multiple output SAR(MIMO SAR)imaging method based on coprime array in range,imaging method of displaced phase center multiple azimuth beams(DPCMAB)based on fractional Fourier transform(FrFT)in azimuth and wide swath imaging of range-azimuth joint multi-antenna SAR based on compressed sensing(CS).The main works and innovation points are as follows.1.The SAR imaging method of high squint is studied.After a detailed derivation and analysis of the echo characteristics of the high squint mode,an extended Chirp scaling(ECS)imaging algorithm is proposed.The echo features are derived and analysed thoroughly,the range migration is removed in time domain,the imaging using the extended chirp scaling algorithm is carried out,and the implementation of this approach is demonstrated.The results show that the range migration is corrected by simple phase addition with appropriate arithmetic and the method is feasible.2.The SAR imaging method of multi-antenna in range is studied.Firstly the waveform of MIMO SAR based on linear frequency modulation pulse signal is designed.Waveform set based on LFM is analysised,and the ambiguity function expression is derived.The Costas encoding combined the LFM signal is designed,which called inter-pulse Costas hopping and intra-pulse slope coded LFM(IPC-SCLFM)signal.Secondly,MIMO-Cop SAR imaging method based on coprime array in range is proposed using IPC-SCLFM signals.The signal model of two kinds of Coprime receiving line array is studied.Echoes are separated by DBF and simple processing of multiply.The cross-correlation noise level is well suppressed and the amount of data is reduced effectively.Finally,the simulation experiments are performed and the results show that the imaging performance is good,and the noise level is well suppressed.3.The SAR imaging method of multi-antenna in azimuth is studied.SAR imaging of moving target from nonuniformly sampled signals with FrFT based on DPCMAB system is proposed.The problem of non-uniform sampling is caused by the dimension error of the antenna,the installation error,and the nonuniform motion of the platform.The nonuniformly sampled points in the fractional order Fourier transform domain are used to reconstruct the moving target detection of DPCMAB system.After the original data is compressed in range,the azimuth reconstruction is carried out,and the reconstructed data is obtained by FrFT,and the Doppler frequency estimation is obtained.Simulation results show that the method is effective.4.The SAR imaging method of multi-antenna in range-azimuth joint is studied.A MIMO SAR imaging based on compressed sensing(CS)is proposed.The sparse array is used in receiving antenna,and the mathematical model of this algorithm is given.The echoes are processed with equivalent DBF and the range resolution is improved.Zero point technique based on CS is proposed with DBF in receive and the range ambiguity is suppressed effectively.Resolution in azimuth is improved by DPCA technique.The simulation results show that the CS technique can effectively reduce the data of MIMO SAR system and the efficiency and validity of the new method is demonstrated.更多还原