一种改进的雷达低空目标仰角估计算法

由于地(海)面反射的多径镜像信号的存在,使雷达低空目标的仰角估计成了难题。而三子孔径算法是针对该难题而提出的一种有效算法。此算法基于极大似然算法将等距线阵均分为三个子孔径,从而简化了估计函数,也使计算量大大减少。本文在三子孔径算法的基础上,利用目标信号与镜像信号在入射角度上的正弦约束条件,给出了一种改进算法。计算机仿真结果显示改进算法在性能上要优于三子孔径算法。     

Angle Estimation with Adaptive Arrays in External Noise Fields

A method of estimating the angle of arrival of a signal at an array of sensors in an external noise environment is outlined. The development is based on a maximum likelihood estimator and leads naturally to adaptive sum and difference beams which null the external noise sources. An algorithm for estimating angle of arrival, based on the outputs of adaptively distorted sum and differnce beams, is shown to perform well in the presence of sidelobe and/or main beam interference.     

一种用于条带模式SAR成像的自聚焦算法

 针对现有条带模式合成孔径雷达（SAR）成像的自聚焦算法中,相位的拼接会引起误差的严重积累,本文结合相位梯度自聚焦（PGA）算法和子孔径偏移（MD）算法,提出了一种新的用于条带模式SAR成像的自聚焦算法（PGA-MD）。该算法先利用PGA算法有效估计各子孔径相位误差函数,再利用相邻子图间方位向偏移量和线性相位之间的关系,通过MD算法精确估计相邻子图间方位向偏移量,然后计算线性相位差,并基于—阶导数实现子孔径相位误差函数拼接。理论分析以及实测数据处理结果对比均表明PGA-MD算法可以有效提高对条带SAR图像的自聚焦效果。     

子孔径拼接测量基本算法与迭代算法的性能比较研究

从原理上对子孔径拼接的基本算法与迭代算法即SASL算法进行了比较分析,提出利用SASL算法中重叠计算子问题的求解方法来确定基本算法中的重叠对应关系,并对两种算法的性能进行了对比研究。结果表明SASL算法对于子孔径的对准误差更不敏感,拼接测量结果更为可靠,且适用于平面、球面和非球面。     

聚束SAR扩展Chirp Scaling成像算法.

在合成孔径雷达（SAR Synthetic Aperture Radar)的成像算法中，Chrip Scaling成像算法具有计算效率高的优点，因此得到了较为广泛的应用。详细研究了子孔径扩展Chirp Scaling算法在高分辩率聚束模式SAR中的应用，包括子孔径划分和方位向处理问题，针对A.Moreira等1996年所提算法在处理聚束SAR数据时所产生的问题，给出了经过改进的适合于大斜视角处理的整个计算过程的完整表达式。在给出点目标仿真的同时，利用E-SAR实际数据对述方法进行了验证，结果对具体的兼容条带和聚束两种工作模式的SAR处理机设计具有一定的参考价值。     

一种基于三维阵列结构二维波达方向估计的新方法

给出了一种在高斯白噪声环境下对多个窄带信号进行二维波达方向估计的新方法.该方法根据给出的天线阵列结构的特点,首先构造四个相关矩阵,进而构造一个大的矩阵,对其进行一次特征值分解,由ESPRIT原理实现了信号波达方向的准确估计.该方法精度较高,不存在错误估计,有一定的实用性.     

Imaging of a compact range using autoregressive spectral estimation[radiation patterns measurement]

The spurious scattering mechanisms of a compact range, which cause spurious signals as well as the desired plane wave to illuminate the test zone, are addressed. It is shown that an accurate estimation of the direction-of-arrival and amplitude of spurious signals in a compact range is beyond the resolution available from the Fourier transform. An estimation technique based on autoregressive (AR) modeling of field probe data is developed to locate and quantify the spurious signal sources. The probe aperture is divided into a number of overlapping subapertures so that the far-field criterion for each subaperture is satisfied. Then, the subaperture data are modeled as an AR process. Singular value decomposition and forward-backward linear prediction are used to estimate the model order and the AR parameters. Examples of probe measurements and analysis for an actual compact range are given     

结合视线方向运动补偿的滑动聚束SAR子孔径成像算法

滑动聚束合成孔径雷达(SAR)是一种新兴的成像模式,既可以提高方位向分辨率又能够扩展成像范围。其数据处理时需要考虑两个关键问题:一是系统脉冲重复频率(PRF)不足,方位向信号发生混叠;二是合成孔径长度的增加使运动误差的影响更为突出,运动补偿(MOCO)精度要求提高。基于子孔径技术,提出了一种改进的高分辨率成像算法。划分子孔径克服了PRF不足的问题;子孔径数据处理采用结合视线(LOS)方向运动补偿的Omega-K算法,实现更高精度的运动补偿,提高了聚焦质量。最终的方位向分辨率达到0.1 m,具有实际工程应用价值。点目标仿真和实测数据处理验证了算法的有效性。     

Detection of moving targets in wideband SAR

A likelihood ratio is proposed for moving target detection in a wideband (WB) synthetic aperture radar (SAR) system. WB is defined here as any systems having a large fractional bandwidth, i.e., an ultra wide frequency band combined with a wide antenna beam. The developed method combines time-domain fast backprojection SAR processing methods with moving target detection using space-time processing. The proposed method reduces computational load when sets of relative speeds can be tested using the same clutter-suppressed subaperture beams. The proposed method is tested on narrowband radar data.     

Angle-of-Arrival Estimation Using an Adaptive Antenna Array

A direction-finding technique is presented that is capable of simultaneously estimating the arrival angles of multiple signals. Pulsed as well as continuous signals can be handled with the signal form only approximately specified. An adaptive antenna array is used as a processing device in the estimation technique. The effect of input signal and feedback loop parameters upon estimate bias is discussed.     

Estimating the Angles of Arrival of Multiple Plane Waves

The problem of estimating the angles of arrival of M plane waves incident simultaneously on a line array with L + 1 (L?M) sensors utilizing the special eigenstructure of the covariance matrix C of the signal plus noise at the output of the array is addressed. A polynomial D(z) with special properties is constructed from the eigenvectors of C, the zeros of which give estimates of the angle of arrival. Although the procedure turns out to be essentially the same as that developed by Reddi, the development presented here provides insight into the estimation problem.     

Characterizing radar emissions using a robust countermeasurereceiver

The author presents a high-sensitivity signal processing approach for detecting and estimating the angle of arrival (AOA), frequency and pulse repetition frequency (PRF) of multiple radar emitters using broadband interferometers. Two time series are generated using information embedded in the sampled cross correlation of the signals obtained from three antenna elements (i.e. two base legs). The phase and amplitude of a complex Fourier transform of these two time series with respect to the sampling clock are used to estimate the AOA and PRF of pulsed emitters     

Comparison of Two Adaptive Methods for Time Delay Estimation

Two adaptive algorithms for estimating the time delay between two-sensor outputs are compared. These methods are similar in that they employ the least mean square (LMS) gradient approach to estimate the time difference of arrival to two sensors. However, they involve the LMS gradient method in different ways, and thus have different properties. Some theoretical aspects are addressed. Also, they are compared via computer simulations for a variety of cases, including time-varying delay functions corresponding to moving source or receivers.     

静止单站纯方位目标航向估计及仿真研究

针对平面直角导航坐标系下匀速直航目标, 利用静止单站测得目标方位序 列, 基于纯方位目标运动分析(BO-TMA)理论, 采用拟线性处理方法, 对目标航向进行 递推式估计。通过多次仿真实验,研究了不同初始条件对目标航向估计性能的影响。该 方法要求简单,便于实现,所得结论为水下隐蔽单站仅利用目标方位信息快速判断敌方 运动态势及作战决策提供了参考。     

Multiple radar targets estimation by exploiting induced amplitude modulation

This work deals with the problem of estimating complex amplitudes, Doppler frequencies, and directions of arrival (DOA) of multiple targets present in the same range-azimuth resolution cell of a surveillance radar. The maximum likelihood (ML) and the asymptotic (large sample size) ML (AML) estimators are derived. To reduce the computational complexity of the maximization of the nonlinear two-dimensional criterion function of the AML estimator, we propose a computationally efficient algorithm based on the RELAXation method. It allows decoupling the problem of jointly estimating the parameters of the signal components into a sequence of simpler problems, where the parameters of each component are separately and iteratively estimated. The proposed method overcomes the resolution limitation of the classical monopulse technique and resolves multiple targets exhibiting an arbitrarily small difference in azimuth as long as their Doppler frequencies differ at least by the inverse of the number of integrated pulses, provided that enough signal-to-noise ratio (SNR) per pulse is available. The performance of the proposed AML-RELAX estimator is numerically investigated through Monte Carlo simulation and Cramer-Rao lower bound (CRLB) calculation.     

Analysis of an adaptive algorithm for unbiased multipath time delay estimation

The multipath equalization time delay estimator (METDE) provides an adaptive approach for estimating the difference in arrival times of a signal received at spatially separated sensors as well as the multipath channel characteristics. However, the parameter estimates of the METDE are biased in the presence of noise. The METDE algorithm is improved for unbiased parameter estimation via minimizing a modified cost function. Convergence behaviors and variances of the system variables of the amended method are derived. Computer simulations are included to corroborate the theoretical analysis and to evaluate the adaptive multipath delay estimation performance of the proposed algorithm.     

导弹协同作战飞行时间裕度

 基于导弹协同作战任务规划系统进行合理任务分配的需求,研究了导弹可以修正控制飞行时间的裕度。根据导弹-目标在视线坐标系和角动量坐标系下的运动关系,得出了导弹相对于目标的加速度,并基于此给出了导弹剩余飞行时间的估算方法;当前时刻导弹剩余飞行时间的估算值与已经飞行的时间以及任务规划系统指定的期望到达时间构成时间反馈作用,用于修正控制导弹到达目标的最终飞行时间。由于真比例导引律在工程实现和解析运算中具有一定的优势,选择在真比例制导加速度的视线方向施加时间反馈控制作用,进而得出了基于真比例导引律的导弹协同作战飞行时间控制导引律;最后重点研究了在该时间控制导引律的作用下,存在导弹的飞行速度限制以及弹目相对运动约束时,导弹飞行过程中任一时刻对应解析形式的可控飞行时间的裕度。仿真结果表明,本文的设计合理可行,对于多弹协同作战的实现具有重要意义。     

Analysis of queuing behavior of automatic ESM systems

Radar electronic support measures (ESM) systems detect active emitters in a given area and determine their identities and bearings. The high arrival rate of radar pulses in dense emitter environments demands fast automatic processing of arriving pulses so that the ESM system can fulfill its functions properly in real time. Yet, the performance analysis of automatic ESM system in real life Is difficult since both pulse arrivals and widths can be specified only probabilistically. The success of queuing theory in many applications such as computer communication networks and flow-control has encouraged designers to utilize queuing theory in qualifying and judging the performance of automatic ESM systems in dense emitter environments. The queuing behavior of these systems is analytically evaluated under different service disciplines and elaborate computer simulations validate the results. The analysis involves statistical modeling of arrival and departure processes as well as distribution of service times. It permits estimating the blocking probability due to high arrival rates of intercepted radar pulses or due to limited speed of the deinterleaver processor. Queuing analysis is shown to be quite useful to quantitatively assess tradeoffs in ESM systems design     

Coherent Doppler tomography-a technique for narrow band SAR

Some concerns regarding a technique of narrowband synthetic aperture radar (N-SAR) imaging called coherent Doppler tomography (CDT), which may be a good candidate for spaceborne applications, are addressed. Using a single-frequency signal, are addressed. Using a single-frequency signal, resolution of two tenths of a wavelength can be achieved in the point spread function if the radar platform circles the ground path to be imaged. However, the high sidelobe level of -8-dB in the point spread function results in an unacceptable dynamic range. To reduce the sidelobe level, two approaches are presented: coherent processing using multiple discrete frequencies and noncoherent subaperture processing. Simulation results demonstrate that the sidelobe level is substantially reduced by both methods. However, the resolution is degraded and the computational overhead is greatly increased for noncoherent subaperture processing. Also presented is a possible satellite geometry configuration that could utilize N-SAR processing to provide high-resolution global mapping capability     

Approximate Maximum Likelihood Algorithm for Moving Source Localization Using TDOA and FDOA Measurements

 A closed-form approximate maximum likelihood (AML) algorithm for estimating the position and velocity of a moving source is proposed by utilizing the time difference of arrival (TDOA) and frequency difference of arrival (FDOA) measurements of a signal received at a number of receivers. The maximum likelihood (ML) technique is a powerful tool to solve this problem. But a direct approach that uses the ML estimator to solve the localization problem is exhaustive search in the solution space, and it is very computationally expensive, and prohibits real-time processing. On the basis of ML function, a closed-form approximate solution to the ML equations can be obtained, which can allow real-time implementation as well as global convergence. Simulation results show that the proposed estimator achieves better performance than the two-step weighted least squares (WLS) approach, which makes it possible to attain the Cram閞-Rao lower bound (CRLB) at a sufficiently high noise level before the threshold effect occurs.