Principles of high-resolution radar based on nonsinusoidal waves.III. Radar-target reflectivity model

For pt.II see ibid., vol.31, no.4, p.369-75 (1989). A target-reflectivity model is developed for carrier-free nonsinusoidal waves with the time variation of a Gaussian pulse or a sequence of positive and negative Gaussian pulses representing a binary code, as was introduced in pt.I (see ibid., vol.31, no.4, p.359-68 (1989)). It is shown that the impulse response of a complex target that is composed of a finite number of scattering centers can be expressed as a sequence of Gaussian pulses. The characteristics of the Gaussian pulses, e.g. peak amplitude and nominal duration, are functions of the physical properties of the scattering centers, which are unique for each target. Hence, the impulse response waveform of a target can be regarded as a one-dimensional image in time (or range), which is valuable information for target classification and recognition. A signal processing technique is developed for obtaining an approximation of a target impulse response waveform from the backscattered and received signals. The signal processor is specifically developed for radar signals with the structure of complementary code pairs whose autocorrelation function is a single narrow pulse with no time sidelobes     

Principles of high-resolution radar based on nonsinusoidal waves.I. Signal representation and pulse compression

Carrier-free coded waveforms that promise good clutter rejection and high-resolution capabilities for radar are represented as a sequence of positive and negative Gaussian pulses. On the basis of this signal representation, the matched-filter (or correlated receiver) response to carrier-free coded waveforms is analyzed and plotted for certain Barker and complementary codes, complementary-code pairs being the optimum codes for clutter rejection. The systematic design of a carrier-free, pulse-compression radar system is described. A correlator receiver that is specifically designed for the selective reception of complementary-code pairs is presented. Computer simulation results for the correlator receiver are also presented     

Resolution function of nonsinusoidal radar signals. II.Range-velocity resolution with pulse compression techniques

For pt.I see ibid., vol.32, no.2, p.153-60 (May 1990). The thumbtack range-velocity resolution function of nonsinusoidal radar signals has been realised with signals having a large number of characters with triangular correlation functions. In reality, a radar signal rarely consists of one pulse; rather, it consists of thousands of pulses structured by various coding techniques. Pulse compression is a technique for obtaining high range resolution with long coded signals. The thumbtack range-velocity resolution function based on the pulse compression principle is realized by coding the transmitted signal using complementary codes. Increasing the code length will increase the pulse compression ratio and the time-sidelobe-free region, Doppler processing of correlation functions based on the pulse compression technique can realize the thumbtack range-velocity resolution function. The range-velocity resolution function is obtained by computer simulation and represented by a three-dimensional surface as a function of target range and velocity for signals with a different number of characters. Plots of range-velocity resolution functions for characters with different code lengths are presented     

Range-velocity resolution function of nonsinusoidal radar signalswith Gaussian time variations

Signal design for carrier-free radars calls for the calculation of a range-velocity resolution function of nonsinusoidal signals consisting of a number of pulses with Gaussian time variations; this is a generalization of P.M. Woodward's (1953) ambiguity function that includes signals that do not have a sinusoidal carrier. Doppler processing of nonsinusoidal signals is investigated in terms of the Doppler effect of pulses with Gaussian time variation and Doppler resolutionl. Doppler resolution is determined in terms of signal parameters. The range-velocity resolution function is obtained analytically and represented by a three-dimensional surface as a function of target range and velocity. Methods for approaching the thumbtack range-velocity resolution function are determined in terms of signal parameters. Several plots for range-velocity resolution function are shown     

Resolution function of nonsinusoidal radar signals. I.Range-velocity resolution with rectangular pulses

A generalization of a previously published ambiguity function that applies to radar known as large-relative-bandwidth radar, carrier-free radar, impulse radar, or nonsinusoidal radar is discussed. This radar has attracted attention because of its ability to penetrate absorbing materials used in the stealth technology. Another good application is the detection of moving targets with a small radar cross section by a look-down radar, which calls for a thumbtack ambiguity function. Since a small radar cross section in this application is typically due to the small size of the target that is coated with absorbing material, the antistealth feature of the nonsinusoidal radar is implicitly being used. The principle is presented of a resolution function (tentatively called the range-velocity or the range-Doppler resolution function) based on processing a nonsinusoidal signal consisting of N characters with a time separation T_D and each character consisting of a sequence of L binary pulses of duration T . It is shown that range-velocity resolution functions approaching the ideal thumbtack function are easy to obtain. The blind speeds of the pulse-Doppler radar with sinusoidal carrier do not inherently occur, and all velocities are observed as true velocities rather than as velocities modulo the first blind speed (velocity ambiguity)     

基于多相码的MIMO雷达模糊函数

从MIMO雷达的特点出发,在双基地雷达模糊函数基础上,提出了MIMO雷达的模糊函数.MIMO雷达的模糊函数是各双基地雷达模糊函数的线性组合,并且双基地雷达的模糊函数是直角坐标系中目标速度和位置的函数.数值计算表明,MIMO雷达的模糊函数具有直接确定目标位置和速度的能力,并且模糊函数与参考点的选取无关,通过增加发射站和接收站的数目能够提高模糊函数的位置分辨率.     

雷达信号模糊函数仿真分析研究

模糊函数是雷达信号理论中极为重要的一个概念,本文对雷达信号中常用的脉冲调幅信号、线性调频信号和巴克码信号的模糊函数进行了计算仿真,并对其进行了分析研究。     

A self-steering array for nonsinusoidal waves based on arrayimpulse response measurement

An array antenna consisting of identical distortion-free sensors used for the reception of nonsinusoidal waves with finite bandwidth is modeled as a linear time-invariant causal system. It is shown that the impulse response of the array sensors is a function of the angle of incidence of the received wavefront. Based on this model, a self-steering array system for beam forming with noise-free rectangular pulses is developed. Its beam-forming mechanism determines the array impulse response to point a main beam in the direction of the source from which the waves are arriving. The array system is advanced further so that nonsinusoidal waves that suffer distortions due to scattering from a large scatterer, and/or dispersive propagation, can be processed to form a main beam in the direction of the scatterer, and to achieve classification and identification of the unknown scatterer     

Acceleration ambiguity function of radar signals and its application

High acceleration of radar targets is analyzed using Acceleration Ambiguity Function(AAF). The acceleration resolution based on AAF is defined. The AAF and acceleration resolution of rectangle pulse signal are derivated and the conclusion that its acceleration resolution is in inverse proportion with the square of its duration is drawn. In the end, these conclusions are applied to the parameter designing and performance evaluation for a certain type of pulse Doppler radar.     

EBPSK调制脉冲数据帧串信号的平均模糊函数

基于EBPSK(Extended binary phase shift keying)调制雷达通信机可输出高精度大量程的雷达测距值.同时利用EBPSK调制脉冲数据帧串信号和冲击滤波辅助解调的特殊优势进行高频谱利用率的数字通信.研究针对EBPSK调制脉冲数据帧串信号的特点,根据cooper给出的随机信号平均模糊函数的基本定义,详细推导了该信号的平均模糊函数,并通过实验仿真了平均模糊函数图.结论表明,随机EBPSK调制脉冲数据帧串雷达信号与随机二相码脉冲雷达信号的距离模糊函数类似,即在距离轴上无模糊,而其速度模糊函数则由随机EBPSK调制数据和周期的相参脉冲串共同决定,即在速度轴上呈“梳状”模糊图,其模糊瓣取决于周期脉冲串.     

Compressive sensing based high-resolution passive bistatic radar

Passive bistatic radar (PBR) systems using different communication signals can only offer low-resolution target detection due to their inherent low bandwidth. In this paper, compressive sensing (CS) is applied to multichannel FM and GSM PBR to achieve improved range-Doppler resolutions and avoid some limitations of classical multiband PBR processing. In CS context, block-structured time-domain dictionary which is formed from multichannel signals suffers from coherence when fine range resolution is employed. To overcome such a pitfall, this work first transforms the dictionary to spectral domain where only the most important spectral components are retained. Principle component analysis followed by a whitening method are then applied to this spectrally transformed data in order to reduce the dimensionality of problem, thereby reducing the dictionary size and most importantly fulfilling the required condition of dictionary incoherence for better CS-based recovery. Two different block-structured dictionary formations are tested. The performance of the recovery of spatially close targets, in both FM and GSM PBR setups, are reported.     

Antenna patterns of nonsinusoidal waves with the time variation ofa Gaussian pulse II

For pt.I see ibid., vol.30, no.4, p.504 (1988). In Part I of this series of papers, antenna patterns for nonsinusoidal waves with the time variation of a Gaussian pulse, received (or radiated) by a linear array of sensors (or radiators) were derived. Computer plots of the peak-amplitude pattern, peak-power pattern, energy pattern, and slope pattern were presented. In this paper, the above antenna patterns are derived for a planar array of sensors (or radiators) receiving (or radiating) Gaussian pulses. Based on the characteristics of the Gaussian pulse, which are presented in Part I, the principle of frequency-domain array beam forming with Gaussian pulses is described. An expression for the antenna energy pattern based on the frequency-domain analysis is derived and plotted for comparison to the one obtained in Part I from the time-domain analysis     

A novel algorithm for side peaks suppression of ambiguity function for passive radar based on chinese DTTB signal

The ambiguity function of Chinese standard Digital Television Terrestrial Broadcasting (DTTB) signals for passive radar contains one main peak and many side peaks. The side peaks may cause the false alarms. The relative positions and the reasons for the side peaks are analyzed and a new algorithm for side peaks suppression is proposed in this paper. The algorithm, in consideration of the characteristics of the structure of the frame, can eliminate the side peaks completely in the valid Doppler observation interval by setting the reference signals to zero at equal intervals. Both the simulative and experimental results show that this algorithm can improve the performance of target detection of the passive radar based on DTTB signal.     

Analytical approximation of the generalized ambiguity function of the MIMO synthetic-aperture radar system

The generalized ambiguity function in spatial coordinates and its approximate analytical representation are obtained for the multifrequency multiple-input multiple-output (MIMO) synthetic-aperture radar (SAR) system. The examples in which ambiguity-function cross sections in range and azimuth are calculated in the Earth remote sensing problem for the MIMO SAR system installed on a spacecraft and compared with those for the classical SAR system are presented. In the case of the MIMO SAR system, the physical meaning and the practical importance of an increase in azimuthal resolution are explained.     

基于部件分解的高分辨雷达目标提取方法

针对传统目标提取算法在低信噪比条件下性能不理想且提取部件不连续的问题,提出一种基于部件分解的高分辨雷达目标提取算法.利用属性散射中心可以表征目标部件的散射回波的优势,通过构造属性散射中心基对目标信号进行分解.通过对分解部件的能量设置门限,提取属于目标的部件.实验结果证明:在低信噪比且虚警概率相同的情况下,基于部件分解的目标提取方法比传统基于像素能量的提取方法能提取出更多且更连续的目标部件.     

基于模糊函数相像系数的雷达辐射源信号分选

针对当前的雷达辐射源信号分选方法存在准确率不高和对噪声敏感的问题,提出一种新的分选算法,对接收到的信号求取其模糊函数,并将其简化为二维特征图,构造一矩形脉冲序列与一三角形脉冲序列,分别求二维特征与两个脉冲序列的相像系数,将求取的相像系数作为分选的特征参数.由于不同信号的模糊函数区别较大且受噪声的影响小,所以转换后的相像系数可分性强、稳定度高,大量的仿真验证了新方法的优越性,在信噪比为10 dB时,分选准确率最低为90%.     

基于双混沌系统的非线性调频雷达信号及其特性分析

提出了两种双混沌系统的构成方案,通过双混沌系统生成了双混沌信号序列,在此基础之上,利用双混沌信号对正弦波进行调频。双混沌调频(FM)信号具有良好的自相关特性,同时使雷达波形难以辨识。用宽带模糊度函数统计平均方法研究了信号的模糊特性,并对信号的抗干扰性能进行了分析。仿真结果表明,双混沌调频信号具有极佳的距离和速度分辨率,抗干扰能力较强,是一种理想的信号形式。     

A remark on radar ambiguity functions (Corresp.)

The ambiguity function of a signalf(t)determinesfup to a constant. Here we explore the extent to whichfcan be modified without affecting the modulus of its ambiguity function.     

基于雷达系统功能的软件测试方法

面对软件高度集成的现代雷达系统,以装备试验学和软件工程学作为理论基础,对雷达系统软件战术指标测试方法进行研究。提出基于系统功能的软件测试方法,用软件测试角度,从雷达系统专业背景考虑,对战术指标进行考核验证,以期通过软件测试发现系统缺陷而不仅仅是软件缺陷。依据相关装备试验原理和软件测试原理,将装备软件测试与装备专业理论相结合,确定测试用例设计方法、等价类划分准则和集合元素选取准则。提出测试策略和测试方法说明。实现从雷达系统专业领域知识对雷达系统软件战术指标进行考核验证的研究目的。