【作者】 赵光辉；

【导师】 陈伯孝；

【作者基本信息】 西安电子科技大学 ， 信号与信息处理， 2008， 博士

【摘要】 基于综合脉冲孔径(SIAR)体制的稀布阵米波雷达发射采用多频正交信号发射,由于不形成发射方向图,其在全空域可以实现等功率能量覆盖,相应的接收自由度可以大大提高;同时由于发射接收天线阵元稀布,通过优化设计阵元位置得到较窄的发射、接收波束以及较低的旁瓣电平,有利于减少多径回波的接收。作为一种米波分布阵体制雷达,该雷达具有良好的反隐身和对抗反辐射导弹的能力,且作用距离远,衰减比微波波段要小,但米波雷达波束宽,角分辨力较差,天线副瓣高,抗干扰能力差等缺点比较明显,特别是俯仰上波束打地,仰角测量精度受到地面(或海面)多径反射的影响较为严重,从而影响了米波雷达对目标高度的准确测量。为针对上述诸多问题,本文从以下几方面展开工作,具体工作概括如下:1.研究稀布阵米波雷达在阵元数有限、阵列孔径有限、水平维和垂直维分别存在最小阵元间距等约束条件下的天线方向图综合问题。该雷达采用稀布天线,为了降低旁瓣电平,天线综合过程中同时考虑发射方向图和接收方向图的影响,将阵元间距的稀疏约束从规则栅格扩展为仅有两维坐标的约束,提出采用二次编码的改进遗传算法,有效地解决了该雷达天线方向图综合中低旁瓣电平设计问题。结合某工程项目给出了某米波雷达天线阵优化结果。2.针对同时辐射多载频的正交信号、收发天线稀布且不共用的基于SIAR体制稀布阵米波雷达,以及在低仰角目标回波存在多径现象等问题,提出一种适用于SIAR体制稀布阵米波雷达的方向综合方法,该方法同时在方位和俯仰两维进行数字波束形成(DBF);并结合多载频工作体制,研究了基于多径相干信号分离的稀疏面阵广义MUSIC算法。该方法将发射天线、接收天线的相位延迟同时补偿,在接收端对发射波束进行两维方向综合,提高了雷达的角分辨力和测角精度;并通过降维处理减少了运算量。3.从模糊函数的角度出发,深入分析了稀疏面阵方位、俯仰二维角度分辨率,详细推导了多径情况下,单目标、多目标的方位、俯仰角度的克拉美·罗界(CRB),为超分辨算法奠定了理论基础。4.针对SIAR体制下稀布阵米波雷达信号处理流程中测距误差对角度测量的影响,考虑到采样过程中距离维存在量化误差,将超分辨思想引入到距离测量中,提出了距离维超分辨处理方法;且由于发射采用多载频信号,回波信号通道分离后若能进行带宽合成,则相应距离分辨率会比单根天线提高数倍,有利于后续检测与跟踪。针对该体制雷达设计中调频带宽和载频差的不同选取,研究分别采用时频域频谱拼接及频谱外推与Root-MUSIC算法相结合的方法,继而得到目标高分辨距离像。5.由于低仰角目标回波中存在多径信号,使得米波雷达难以对低仰角目标进行高度测量,为此提出一种适用于多径信号情况下的波达方向估计的迭代方法。该方法将回波信号的相关矩阵,在各个信号子空间中交替投影,可以同时对直达波和反射波进行较精确的波达方向估计,进而有效解决了米波雷达低仰角目标高度测量问题;结合平坦阵地反射模型,提出一种适用于多径情况下的波达方向估计方法。该方法通过差分处理,补偿了多径信号回波相位,使得接收回波中仅包含直达波信号,对差分后数据进行常规数字波束形成即可得到目标俯仰角。上述方法通过某米波试验雷达的实测数据进行了可行性与有效性验证。更多还原

【Abstract】 The spacial energy is uniformly distributed as the transmitting signals are orthogonal to each other,which are emited simultaneously by MIMO radar.Its theory could be originated from SIAR when the radiated orthogonal signals are in the form of orthogonal phase-coded and frequency-coded to each other.As multiple frequency signals are used,the coherent echo could be resolved;as the array elements are sparsely located,to guarantee obtaining lower sidelobes in the process of synthesizing transmitting and receiving directions,the positions of the elements could be optimized to avoid the effection of the multipath propagation.As a kind of meter-wave radar,it has better performance in anti-and anti-arm,long effectom range,its attenuation is little compared with microwave radar.The meter-wave radar has more geat inspection ability on slow velocity target.But as it has wide beam, the angle resolution is worse than others,its sidelobe is usually high,which prevent the anti-disturb ability.Espacilly when the beam is irradiated on the ground,more than one path multipath echo come into the target echo which great effect the measurement of the target angle.To overcome the above problem,several methods are proposed in this paper,the concrete contents are as follows:1.For the constraints of the number of element,the limited array aperture and the minimum element spacing in both horizontal and vertical dimensions,the optimization of array pattern synthesis in MIMO radar is presented in this paper.To lower the sidelobe level,both the transmitting and receiving patterns should be considered in the MIMO radar where sparse arrays are used.Extending the sparse constraints of regular grid to the constraints of inter-element distances in a plane,an improved multiple genetic algorithm by coding twice is proposed,with which the problem of pattern synthesis in MIMO radar with lower maximum relative sidelobe level is solved effectively.The optimal algorithm used in practical design is presented.The simulated results confirm the validity of this method in this paper.2.A new direction synthetic method for sparse array meter wave radar is presented based on synthetic impulse and aperture radar(SIAR) system.Concerned with the kind radar which simultaneously emits orthogonal signals with multi-carrier-frequency and possesses sparsely distributed transmitting and receiving arrays with respective location,as well as the situation for the presence of multipath propagation in the low flying target’s echo,the method form the digital beam-forming(DBF) in azimuth and elevation dimensions.And a study has been made of planar general MUSIC algorithm based on decorrelating the multipath signals of multi-carrier-frequency radar.Through compensating the phase delay of both the transmitting and the receiving arrays and synthesizing the transmitting beam in two dimensions at the receiver,the angular resolution and measurement accuracy are improved and the computational complexity is reduced after transforming the three-dimensional(3-D) parameter estimation problem into a two-dimensional(2-D) one.3.From an introduction of the four dimensional ambiguity function of the transmitted signals, the angle resolution in both transmitting array and receiving array are studied.After the study of the signal model of the meter-wave radar,the detailed deduction of the CRBs of DOA estimation for azimuth and elevation for one target and multiple targets have been obtained,the comparison of CRB have been discussed through simulation and which make a theory basis for the study of super-resolution algorithm.4.As the error in the measurement of the target distance could effect the measurement in azimuth and elevation,considering that there are quantification errors in distance-dimension during the echo sampling,the idea of super-resolution is introduced into distance measuring and elaborate the procedure of super resolution.While for this kind radar,as multi-carrier-frequency signals are transmitted simultaneously,if the spectrum of the target echo after channel separation could be combined to form the whole band spectrum echo,the corresponding range resolution will be improved several times than conventional method,and it will be more convenient for detection and tracking.Considering the difference between the frequency modulation band and the interval between the adjacent frequencies,the spectrum joint after channel separation will be overlap or space.Methods of spectrum moving of each echo and the spectrum extrapolation with Root-MUSIC algorithm are proposed in this paper,by using which high resolution range image of the target could be obtained.5.In the presence of multi-path propagation,it is quite difficult for VHF radar to measure the altitude of a low elevation target.In this paper,a new alternating projection algorithm is proposed to estimate the DOA of the target.By projecting the correlation matrix of the target echo into different signal subspaces,this method can be used to estimate accurately the directions of both the direct wave and the reflected wave,and hence the altitude of the target is known precisely;another mehtod which is based on the flat position refleciton mode is proposed,which by using the differential preprocessing,the phase of the multipath wave can be compensated,the echo from multi-path propagation can be subtracted form the signal that received.Then the general DBF can be used to estimate the direction of the direct wave.The real data from some VHF radar demonstrates the validity and feasibility of the both new algorithm.更多还原