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)     

High-resolution nonsinusoidal radars with three-dimensional targetstructure

A 3D target structure along with a coordinate system transformation will enable a high-resolution ground-based radar looking up at a target or an airborne radar looking down on a target to perform target recognition at all azimuth and elevation or look-down angles. Target dimensions such as length, width, and height are characterized by a three-dimensional surface as a function of azimuth and elevation angles. Target signatures for transmitted pulses with beta time variation are obtained as a function of target extent, azimuth, and elevation or look-down angles. An average range resolution is defined to accommodate the large variation in range resolution with target orientation. Target recognition based on target shape can distinguish airplane targets with a variable structure, though the database may not contain a matched sample target signature to the observed one. A distributed ground clutter model has been analyzed to obtain ground clutter variations with azimuth and elevation angles. In addition, the peak magnitude of clutter-to-signal ratio has been determined for a clutter area with a varying number of point scatterers. The analysis and target recognition of a radar receiver consisting of a sliding correlator to suppress noise followed by a three-pulse canceller to eliminate clutter has been carried out in terms of input target signatures     

频率步进雷达及其在小目标检测中的应用

在强杂波环境下检测一类重要小目标（如巡航导弹，反舰掠海导弹，隐身飞机）是现代雷达面临的一个最具有挑战性的课题。频率步进雷达，由于其高距离分辨能力及独特的波形和处理，正在用来解决强杂波中小目标的检测问题。文中首先介绍了频率步进宽带高距离分辨雷达的原理和技术，然后讨论了应用频率步进雷达解决强杂波中运动小目标的无杂波区检测和无折叠杂波检测问题。     

Target course recognition using nonsinusoidal look-down radars

The target signature of an airplane as viewed by a nonsinusoidal look-down radar is obtained analytically as a function of target shape, azimuth orientation, look-down angle, and transmitted pulse duration. The information contained in the target signature can be used for detection of stationary and moving targets in heavy clutter, as well as the recognition of target shape and orientation. The relation between target signature and target azimuth orientation shows that pulse lengths shorter than airplane length are required to perform target recognition at all azimuth angles. Target course recognition in the radar ground plane is the process of determining the azimuth angle by selecting from the database the target signature that is most similar to the observed one. The effect of look-down angle on the target signature is also analyzed. At small look-down angles, target shape information is obtained with pulse lengths shorter than aircraft length. However, at large look-down angles pulse lengths much shorter than the airplane length are required. The variation of the target signature with azimuth and look-down angles are utilized for determining two-dimensional target course recognition. Cruise missile radars operating in a lookdown mode can utilize the very-high-resolution nonsinusoidal radar to enhance target shape recognition in addition to target course recognition     

基于DEM数据机载气象雷达地杂波抑制方法

针对机载气象雷达工作于气象模式时地杂波的抑制问题,应用基于地形可视化的方法在时域对地杂波进行抑制的方法.首先分析机载气象雷达下视时气象目标和地杂波的分布特点,然后根据DEM（DigitalElevation Model）表达地形的特点,利用增量法对地形进行可视化判断.对于气象雷达扫描区域内的可视化点判断其所在的距离单元.将这些贡献地杂波的单元予以剔除.通过仿真实验验证了该方法的有效性.     

低空雷达导引头海面目标检测性能分析

该文以雷达导引头低空检测海面目标为背景,综合分析了多径环境和海杂波环境对雷达导引头目标检测的影响。通过对目标回波、多径散射的镜反射、漫反射以及海杂波进行建模,结合具体场景,仿真分析了镜反射、漫反射以及海杂波对雷达导引头接收信号的影响,进而分析了多径散射和海杂波对雷达导引头检测不同大小目标时检测性能的影响效果。仿真结果表明:雷达导引头检测RCS低于1 m2的小目标时,海杂波是影响雷达导引头检测性能的主要因素;雷达导引头检测RCS大于10 m2的目标时,多径效应是影响雷达导引头检测性能的主要因素;雷达导引头检测RCS大于104 m2的目标时,雷达导引头的检测性能不受海杂波和多径效应影响。     

New techniques applied to air-traffic control radars

During the past two years a program has been carried out to show how new techniques can greatly improve the performance of radars used for air-traffic control. A survey of problems associated with presently used radars was undertaken. This survey indicates that primary radar in an automated air-traffic control system can be made significantly more effective by the use of new techniques. The radar's handling of extraneous reflections (clutter) is critical to its performance. Three types of interfering clutter were found to predominate: ground clutter, weather clutter, and angels. Angels are generally accepted to be radar returns from flocks of birds. In addition, second-time-around clutter is often troublesome. For each type of clutter, all known remedies for improving the signal-to-clutter ratio were studied and radar systems were configured using appropriate sets of remedies. Some specific solutions incorporated in the resulting radar systems are: a) the use of linear large dynamic range, near-optimum digital signal processors to filter signals from clutter, b) the use of electronically step-scanned antennas to improve the correlation of aircraft and clutter returns from pulse to pulse, c) the use of multiple PRF's instead of staggered PRF's together with coherent transmitters to keep second-time-around clutter returns well correlated while still overcoming blind speeds, d) the use of a fine grained ground clutter map to give superclutter visibility on tangential targets, and e) the use of lower operating frequencies to greatly reduce weather and angel returns. Two demonstration radar systems have been implemented, an S-band radar using a mechanically rotating antenna and a UHF radar using an electronically step-scanned cylindrical antenna. Experimental results are described.     

基于起伏RCS模型的机载PD雷达相干视频杂波模拟

文中基于起伏散射截面积RCS,对机载脉冲多普勒(PD)雷达的地杂波仿真问题,介绍了基于相干视频信号的模拟方法,给出了具体的公式、原理和步骤。此方法有三个优点:首先,有利于地面散射环境的模拟,其次,用起伏的RCS代替平均RCS,增强了杂波模拟的真实性,最后,由于采用了相干视频信号使杂波的仿真可以应用于信号级的系统仿真中。文中对不同脉冲重复频率(PRF)下的地杂波进行了仿真和分析,讨论了距离模糊和多普勒模糊对杂波谱的影响。仿真结果与理论计算吻合较好,表明这种估算地杂波的方法正确有效。     

基于熵的步进频率探地雷达距离旁瓣抑制

步进频率探地雷达因频谱截断和杂波干扰而产生严重的拖尾旁瓣,降低了系统分辨目标的能力。文中分析了熵表征的信号特征,从距离旁瓣产生的机理出发,提出用最大熵、最小熵谱外推技术对截断频谱外推,降低频谱截断产生的拖尾旁瓣。实验结果表明,最大熵可以有效地去除因频谱截断产生的Gibbs振荡,最小熵对峰值旁瓣电平抑制效果较好,两者都有效地提高了系统分辨率。     

运动目标回波与地表杂波的多普勒频移的仿真

由双站雷达方程与地表双站散射杂波的模拟,对寻的导弹接受运动目标回波与地表杂波的多普勒频移建立了数值仿真程序,数值模拟在俯射、等高、仰视、尾追等情形下地表杂波对半主动雷达对半主动雷达寻的导弹制导的影响。结果表明,俯射时杂波主瓣有一很高电平,并随着俯角的减小而降低。在这种情形下,如果目标作适当横向机动,目标信号可能完全被杂波主瓣掩盖。当目标超低空飞行时,杂波旁瓣电平将相当地高。文中对导弹半主动雷达寻的     

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     

连续混沌调频雷达信号分析

该文给出了连续混沌调频信号(CCFMS)的数学表达式,理论推导了CCFMS的自相关函数和均方根带宽。结果表明CCFMS自相关函数的旁瓣抑制性能优异;其均方根带宽与调频指数、混沌信号的均方根成正比。仿真计算了典型混沌产生的CCFMS性能,进一步证明了CCFMS具有较高的时间峰值旁瓣比、平坦的功率谱形状、近似图钉型的模糊函数和与正弦发射信号相同的峰均功率比。分析了CCFMS雷达的抗噪声干扰性能,与线性调频信号雷达相比,信干比改善因子提高约5.5 dB。     

Siting of Doppler weather radars to shield ground targets

Weather radars are usually sited so they can survey as large an area as possible. A large surveillance area is achieved by placing the antenna as high as practical but then the radar can be blind to weather targets near the ground because of ground clutter interference. There are applications where it is necessary to have fine resolution of low altitude divergence and wind shear near the ground in regions of weak weather reflectivity. This requirement can be most conveniently satisfied when surveillance is near the radar, but it brings attention to the problem of reducing ground clutter. Although cancelers help to reduce ground target echoes, they cannot eliminate them, and reduction for scanning beams is limited to about 40 dB. Proper siting to take advantage of natural terrain and man-made shields (clutter fences) can further reduce ground clutter. Criteria are developed that relate ground target illumination to antenna characteristics, shield heights, and the distance to the shield. Both geometric optic and diffraction theory are used to estimate the effectiveness of shields.     

海杂波背景下的低空小目标检测

海面上低空小目标通常具有RCS（雷达散射截面）小、速度快的特点,并且容易湮没在海杂波背景中,很难被雷达系统检测到。文中首先分析了海杂波数据的统计特性;然后在此基础上,利用海杂波和目标在相关特性上的差异,提出了一种熵加权非相参积累方法,该方法能够抑制海杂波,并且积累目标能量;为了进一步降低检测门限,采用了TBD（检测前跟踪）技术。某S波段雷达搜索模式下低分辨实测数据的处理结果表明,熵加权非相参积累和TBD方法能够有效降低海杂波背景下低空小目标信号的最小可检测信杂比。     

直升机雷达下视模式杂波分析

以直升机雷达平台为背景,分析了机载雷达下视模式的杂波特性。首先分析了天线不同的安放角的时间-空间二维杂波谱的特性,并研究了前向阵在不同波束位置杂波的多普勒频率与斜距离的变化关系,运用了海杂波和地杂波模型计算LPRF和HPRF两种雷达工作模式下距离-多普勒杂波功率谱,最后给出了以直升机为平台的X波段雷达仿真结果,文中的杂波特性可以在系统设计时参考。     

Moving target feature extraction for airborne high-range resolutionphased-array radar

We study the feature extraction of moving targets in the presence of temporally and spatially correlated ground clutter for airborne high-range resolution (HRR) phased-array radar. To avoid the range migration problems that occur in HRR radar data, we first divide the HRR range profiles into low-range resolution (LRR) segments. Since each LRR segment contains a sequence of HRR range bins, no information is lost due to the division, and hence, no loss of resolution occurs. We show how to use a vector auto-regressive (VAR) filtering technique to suppress the ground clutter, Then, a parameter estimation algorithm is proposed for target feature extraction. From the VAR-filtered data, the target Doppler frequency and the spatial signature vectors are first estimated by using a maximum likelihood (ML) method. The target phase history and direction-of-arrival (DOA) (or the array steering vector for an unknown array manifold) are then estimated from the spatial signature vectors by minimizing a weighted least squares (WLS) cost function. The target radar cross section (RCS)-related complex amplitude and range-related frequency of each target scatterer are then extracted from the estimated target phase history by using RELAX, which is a relaxation-based high-resolution feature extraction algorithm. Numerical results are provided to demonstrate the performance of the proposed algorithm     

一种改进的球载雷达气象杂波建模方法

球载雷达由于雷达平台的升高并采用下视工作,面临着强的地海杂波和气象杂波。针对径向速度较小的目标落在气象杂波区会降低雷达检测性能这个问题,为了更好地抑制气象杂波,本文提出了一种球载雷达气象杂波建模方法。首先建立了气象杂波的空间模型和数学模型,然后分析了气象杂波的分辨特性和幅度频率特性,基本完成了球载雷达杂波建模。最后通过对杂波建模仿真及其MTD结果的分析,进一步揭示了气象杂波的特性,为下一步探讨球载雷达杂波抑制方法提供了支撑。     

机载杂波测量雷达的有源绝对校准技术研究

雷达系统的精确校准是保证地海杂波测量数据可靠性的关键问题.本文利用地面有源雷达校准器(ARC)对L波段HH极化机载杂波测量雷达进行绝对校准,通过ARC设计、目标提取以及坐标系变换技术,充分考虑了校准场地背景杂波、载机姿态和GPS误差等因素对雷达系统常数、时延和天线方向图的影响.分析结果证明了这一技术的有效性.     

高分辨雷达目标检测方法研究

高分辨雷达较低分辨雷达能够提供较多的目标结构信息,但是由于其目标回波和杂波的特殊性,信号检测也存在着一些新的技术问题。本文分析了高距离分辨雷达目标和杂波的回波特性,给出了回波模型,在此基础上分析了非瑞利杂波背景下高距离分辨雷达的检测方法,并进行了仿真验证,结果表明采用TM—CFAR与M／N检测相结合的方法可以很好的利用...     

PRC-CW雷达地杂波相关特性分析

本文分析了在低俯视角情形时地杂波要引起雷达回波信号展宽的事实,对于伪码调相连续波雷达来讲,某一时刻的回波信号将是此前一段时间内展宽的回波在此时刻的迭加,提出了计算伪码调相连续波雷达回波信号的迭加方法,在以往对地杂波特性研究结果的基础上,同时考虑了不同分辨单元间在空间和时间上的相关性质,研究该体制雷达地杂波回波信号的时间相关特性,并进行了计算机模拟,结果表明,与脉冲雷达相比,其地杂波的时间相关性将增