Analysis of Random Step Frequency Radar and Comparison With Experiments

Linear stepped frequency radar is used in wide-band radar applications, such as airborne synthetic aperture radar (SAR), turntable inverse SAR, and ground penetration radar. The frequency is stepped linearly with a constant frequency change, and range cells are formed by fast Fourier transform processing. The covered bandwidth defines the range resolution, and the length of the frequency step restricts the nonambiguous range interval. A random choice of the transmitted frequencies suppresses the range ambiguity, improves covert detection, and reduces the signal interference between adjacent sensors. As a result of the random modulation, however, a noise component is added to the range/Doppler sidelobes. In this paper, relationships of random step frequency radar are compared with frequency-modulated continuous wave noise radar and the statistical characteristics of the ambiguity function and the sidelobe noise floor are analyzed. Algorithms are investigated, which reduce the sidelobes and the noise-floor contribution from strong dominating reflectors in the scene. Theoretical predictions are compared with Monte Carlo simulations and experimental data     

一种线性调频信号超低旁瓣脉冲压缩方法

雷达脉冲压缩希望具有超低距离旁瓣的特征,线性调频信号采用加窗方式可达到约-35 dB的距离旁瓣电平。基于超低旁瓣电平信号设计方法,在不考虑信噪比损失条件下,提出了一种新的超低旁瓣的脉冲压缩方法,基本思想是针对给定线性调频信号,频率滤波权值采用超低频旁瓣频域信号与线性调频信号频域的比值,可以将接收端旁瓣电平输出最低到-120 dB。同时,从理论上和数值结果中分析了信噪比损失、延迟敏感性等问题。     

Pulse compression for weather radars

Wideband waveform techniques, such as pulse compression, allow for accurate weather radar measurements in a short data acquisition time. However, for extended targets such as precipitation systems, range sidelobes mask and corrupt observations of weak phenomena occurring near areas of strong echoes. Therefore, sidelobe suppression is extremely important in precisely determining the echo scattering region. A simulation procedure has been developed to accurately describe the signal returns from distributed weather targets, with pulse compression; waveform coding. This procedure is unique and improves on earlier work by taking into account the effect of target reshuffling during the pulse propagation time which is especially important for long duration pulses. The simulation procedure is capable of generating time series from various input range profiles of reflectivity, mean velocity, spectrum width, and SNR. Results from the simulation are used to evaluate the performance of phase coded pulse compression in conjunction with matched and inverse compression filters. The evaluation is based on comparative analysis of the integrated sidelobe level and Doppler sensitivity after the compression process. Pulse compression data from the CSU-CHILL radar is analyzed. The results from simulation and the data analysis show that pulse-compression techniques indeed provide a viable option for faster scanning rates while still retaining good accuracy in the estimates of various parameters that can be measured using a pulsed-Doppler radar. Also, it is established that with suitable sidelobe suppression filters, the range-time sidelobes can be suppressed to levels that are acceptable for operational and research applications     

基于网络综合法脉冲压缩信号的旁瓣抑制

脉冲压缩信号在雷达系统中有着广泛应用,而一直以来旁瓣抑制问题也备受关注。通常,时宽带宽积(BT)较大的线性调频信号可通过单一加窗实现较低旁瓣,但对于其它脉冲压缩信号效果甚微,文中提出的基于网络综合的旁瓣抑制的频域设计方法则适用于各种脉冲压缩信号。线性调频和二相编码混合信号兼备线性调频和相位编码信号的特点,因此文中以此信号为例进行了仿真,分析表明采用网络综合法进行旁瓣抑制,旁瓣效果理想且对多普勒频移不敏感。     

线性伸缩波形的雷达距离模糊特性及旁瓣抑制

该文提出了任意信号的时域线性伸缩表达式,给出了一类新的雷达波形,并对这类波形的压缩形式(匹配滤波输出)在时域进行旁瓣抑制数字滤波。仿真结果表明,这类波形的距离模糊函数的峰值旁瓣电平可达-18~-20 dB,而4dB主瓣宽度仅为相同参数的线性调频(LFM)压缩信号主瓣宽度的54%~70%;对这类波形的匹配滤波输出用该文改进的数字旁瓣抑制滤波器滤波后,其峰值旁瓣电平可低达-50dB,且主瓣宽度仅为单位采样符号长度。     

一种新的低旁瓣LFM噪声雷达波形设计方法

针对LFM噪声雷达波形旁瓣功率水平高的问题,该文将低旁瓣波形设计方法和LFM噪声雷达波形设计方法相结合,提出一种新的低旁瓣LFM噪声雷达波形设计方法。该方法首先建立低旁瓣LFM噪声雷达波形设计目标函数,将确定性二次相位和随机相位的组合关系转化为优化问题的约束条件,然后通过该文提出的修正循环算法(MCAN)迭代求解,使得设计的恒模LFM噪声波形同时具有低旁瓣和高多普勒容忍性。最后,仿真结果表明该算法能够降低波形模糊函数的距离-多普勒2维旁瓣,对静止目标和运动目标均能够起到较好的效果,且保证了波形的低截获概率性能。     

超视距雷达中窄带干扰抑制技术研究

超视距雷达中,发射信号带宽的选择受到密集的大功率干扰的限制,很难找到较宽的且未被污染的干净频带,导致了很低的距离分辨力和信干噪比,较为理想的方法是在一定的带宽要求下抑制干扰.考虑到直接用凹口滤波零陷干扰时,脉冲压缩后副瓣迅速抬高,目标信号淹没在干扰的旁瓣之中,本文提出了抑制旁瓣干扰的投影算法和时域自适应对消方法.理论分析和仿真结果表明:投影法计算量小,副瓣得到一定的降低,但需要设计子带滤波器组,且引入了暂态响应;而自适应对消方法虽然计算量稍大,但通过自适应调整权值可很好地抑制掉旁瓣干扰,脉压后副瓣电平大大降低,有效地提高了目标检测能力.     

应用正交码组信号的传统雷达距离旁瓣抑制方法

为了抑制传统雷达的距离旁瓣和提高传统雷达抗欺骗式干扰性能,该文提出一种传统雷达随机发射一组正交信号的信号发射策略。给定一组正交性好且距离旁瓣低的相位编码信号,雷达在每次发射时从这组波形中随机选取一个波形进行发射,接收端已知该发射信号波形并基于该波形对接收信号进行脉冲压缩,最后对多次相邻脉冲的回波信号进行相干积累。理论分析和仿真结果均表明,距离主瓣信号能够有效积累,而距离旁瓣信号近似白化,因而脉冲积累后可明显降低系统的最大距离旁瓣电平。     

对调频连续波SAR部分接收式噪声调制干扰

调频连续波合成孔径雷达（FMCW SAR）作为成像雷达小型化产物,其结构简单、成像分辨率高、系统隐蔽性强,需要对其进行快速有效的干扰。本文提出了一种对FMCW SAR部分接收式噪声调制干扰方法,将信号时域与噪声频域进行乘积调制,能够生成范围可控的灵巧压制区。同时截获信号采用部分接收的方式处理,并将部分接收信号通过多次移频补偿与首尾衔接以模拟完整周期截获信号,避免了对FMCW大时宽带宽信号采样时带来的数据庞大问题,降低信号带宽、减小采样数据与调制运算量。另外,部分接收使得干扰出现旁瓣扩散现象,将会分散主要压制区的部分能量。本文方法通过仿真验证了可行性,其能够降低算法复杂度与硬件压力,并通过改变噪声模板时宽实现对压制区范围的灵巧控制,故具有工程可行性。     

基于5G信号的脉压加权相参积累方法

5G信号携带的通信信息导致脉压信号出现大量随机性起伏旁瓣,类似于噪声对脉压信号的干扰,影响了相参积累性能.针对该问题,本文将脉压信号幅度加权的方法应用到基于5G信号的外辐射源雷达系统中,在单发单收的雷达模型基础上,理论分析了5G信号特性及脉压旁瓣起伏性较大原因,推导了脉压幅度加权方法抑制随机性旁瓣的可行性.最后,通过建...     

单脉冲脉内互补低距离旁瓣雷达波形设计

雷达脉冲压缩的距离旁瓣较高将会导致遮蔽效应的产生,已有的低旁瓣波形设计都是基于全脉冲相关进行处理。本文利用波形组合的方法进行波形设计,基于单脉冲脉内分段脉压信号处理方式和互补码自相关求和零旁瓣特征相结合,利用频域正交设计,将两个或多个互补序列调制至不同频点以子脉冲的形式分段合并为恒模单脉冲雷达波形。仿真试验表明,本文设计的单脉冲脉内互补低旁瓣波形脉压后的峰值旁瓣电平和积分旁瓣电平较低,分段脉压结合互补码零旁瓣特征的信号处理方式虽然会导致0.89 dB左右的信号处理增益损失和主瓣展宽,但却能够突破部分相位编码信号的峰值旁瓣电平下限。强弱目标场景仿真表明,与线性调频信号相比,本文提出的雷达波形不会导致强目标的副瓣对弱目标的遮掩。恒虚警检测仿真表明,在剔除强目标峰值后,本文所提波形对弱目标的检测概率要优于传统的线性调频信号。     

Ambiguity functions of laser-based chaotic radar

The ambiguity functions of a newly developed laser-based chaotic radar (CRADAR) system are studied. In the CRADAR system, the chaotic waveforms can be generated either by an optically injected (OI) semiconductor laser, or a semiconductor laser with optoelectronic feedback (OEF). The ambiguity functions of the chaotic pulsation and chaotic oscillation waveforms obtained experimentally from the CRADAR system with the respective OEF and the OI schemes are examined and compared. In the cross-ambiguity functions, both types of the chaotic waveforms demonstrate their excellent capabilities in the electrical counter-countermeasures (ECCM) that civilian and military applications desire. In the auto-ambiguity functions, the chaotic oscillation waveform shows better unambiguous detection quality than the chaotic pulsation waveform that an ideal thumbtack-like ambiguity function with minimal sidelobes is found. Moreover, variations in the peak value and the full width at half-maximum of the auto-ambiguity function of the chaotic oscillation waveform along the principal axes are also investigated. By having the features of both ultrawideband radar and random signal radar, the chaotic oscillation waveform of the CRADAR system with the OI scheme is shown to possess the advantages of high range resolution, excellent ECCM capability, ideal thumbtack-like ambiguity function, and uncoupled range and range rate resolution functions.     

OFDM MIMO radar waveform design for targets identification

In order to obtain better target identification performance, an efficient waveform design method with high range resolution and low sidelobe level for orthogonal frequency division multiplexing (OFDM) multiple-input multiple-output (MIMO) radar is proposed in this paper. First, the wideband CP-based OFDM signal is transmitted on each antenna to guarantee large bandwidth and high range resolution. Next, a complex orthogonal design (COD) is utilized to achieve code domain orthogonality among antennas, so that the spatial diversity can be obtained in MIMO radar, and only the range sidelobe on the first antenna needs suppressing. Furthermore, sidelobe suppression is expressed as an optimization problem. The integrated sidelobe level (ISL) is adopted to construct the objective function, which is solved using the Broyden-Fletcher-Goldfarb-Shanno (BFGS) algorithm. The numerical results demonstrate the superiority in performance (high resolution, strict orthogonality, and low sidelobe level) of the proposed method compared to existing algorithms.     

相控阵天气雷达脉压距离旁瓣抑制研究

针对所采用的脉冲压缩技术带来的距离旁瓣影响大气测量的问题,文中首先描述了脉冲压缩技术的特点和脉冲压缩技术的原理,使用MATLAB语言工具,仿真计算了线性调频、非线性调频和相位编码等波形脉冲压缩以后距离旁瓣的水平,并分析了这几种脉冲压缩波形对距离旁瓣抑制的效果,给出了适合相控阵天气雷达大气探测使用的波形.     

Validation of pulse compression techniques for meteorologicalfunctions

A major technology barrier to the application of pulse compression techniques in meteorological radar is the presence of range sidelobes which mask and corrupt observations of weak weather phenomena in areas of strong extended meteorological scatterers or point target returns. Techniques for suppressing range sidelobes are well known, but without prior knowledge of the scattering medium's velocity distribution their performance degrades rapidly in the presence of doppler. Recent investigations have presented a “doppler tolerant” range sidelobe suppression technique. The thrust of the work described in this article is the extension of previous simulations to the transmission of dispersed/coded waveform pulses using the ELDORA X-Band weather research radar located at the National Center for Atmospheric Research (NCAR) Foothills Laboratory. This study shows that the use of Barker coded pulses along with pulse compression and doppler tolerant range sidelobe suppression provides: (1) increased sensitivity over a simple pulse of the same peak power, and nominal receive bandwidth by a factor equal to the time-bandwidth product, and (2) accurate spectral moment estimates     

Effective CLEAN algorithms for performance-enhanced detection of binary coding radar signals

With binary coding waveform as radar pulse compression signal, the sidelobe of the matched processing result of the received signals is a serious interference to the effective detection of multiple targets. In this paper, the CLEAN algorithms are introduced to eliminate such sidelobes and significantly improve the target detection performance of binary coding radar signals. A novel modified CLEAN algorithm is proposed to remove the sidelobe interferences in formulating target range profile when wideband binary coding signals are used. The effectiveness of the CLEAN algorithms is demonstrated through the processing results.     

MIMO探地雷达随机步进频信号旁瓣抑制

针对MIMO探地雷达中随机步进频信号的距离旁瓣较高的问题,提出了一种基于快速二阶锥优化问题的旁瓣抑制方法。该方法首先通过建立随机步进频信号模型对回波信号进行预处理,然后基于回波信号的旁瓣特点将旁瓣抑制问题转化为以信号的峰值旁瓣构建目标函数,以主峰损失、峰值旁瓣和积分旁瓣联合约束的二阶锥优化问题,最后使用内点法求解二阶锥规划问题,以此得到最优的旁瓣滤波器系数。仿真和实测数据处理结果表明,设计的失配滤波器能够在较低主峰损耗的情况下,有效降低峰值旁瓣电平和积分旁瓣电平,提高信号的主旁瓣比。该方法为MIMO探地雷达中的距离旁瓣问题提供了有效解决思路,有望在工程应用中提高探地雷达的性能。     

Tutorial review of synthetic-aperture radar (SAR) with applications to imaging of the ocean surface

A synthetic aperture radar (SAR) can produce high-resolution two-dimensional images of mapped areas. The SAR comprises a pulsed transmitter, an antenna, and a phase-coherent receiver. The SAR is borne by a constant velocity vehicle such as an aircraft or satellite, with the antenna beam axis oriented obliquely to the velocity vector. The image plane is defined by the velocity vector and antenna beam axis. The image orthogonal coordinates are range and cross range (azimuth). The amplitude and phase of the received signals are collected for the duration of an integration time after which the signal is processed. High range resolution is achieved by the use of wide bandwidth transmitted pulses. High azimuth resolution is achieved by focusing, with a signal processing technique, an extremely long antenna that is synthesized from the coherent phase history. The pulse repetition frequency of the SAR is constrained within bounds established by the geometry and signal ambiguity limits. SAR operation requires relative motion between radar and target. Nominal velocity values are assumed for signal processing and measurable deviations are used for error compensation. Residual uncertainties and high-order derivatives of the velocity which are difficult to compensate may cause image smearing, defocusing, and increased image sidelobes. The SAR transforms the ocean surface into numerous small cells, each with dimensions of range and azimuth resolution. An image of a cell can be produced provided the radar cross section of the cell is sufficiently large and the cell phase history is deterministic. Ocean waves evidently move sufficiently uniformly to produce SAR images which correlate well with optical photographs and visual observations. The relationship between SAR images and oceanic physical features is not completely understood, and more analyses and investigations are desired.     

相位编码信号的综合旁瓣能量改善技术

相位编码信号的综合旁瓣性能不佳是制约其在分布式目标观测应用中的主要因素。根据相位编码信号的均匀旁瓣结构有利于抑制旁瓣能量的性质,采用失配滤波技术对接收回波处理,获得了基本均匀的旁瓣输出,进一步通过接收回波提取出原始发射信号分量,通过一位时移、取复共轭形成了旁瓣对消器,经过旁瓣对消处理后极大地改善了相位编码信号的积分旁瓣比指标值,并且获得了类似线性调频信号的多普勒容忍性,本方法将使得相位编码信号在雷达对地观测等方面获得很好的应用前景。     

基于特征参数的随机噪声雷达相关输出研究

随机信号的数字特征参数是信号分析的重要因素,是随机信号波形设计的依据。相关系数和方差是随机信号的两项具有决定作用的特征参数。以随机噪声雷达的一般性相关输出模型为基础,建立了基于相关系数和方差表达的相关输出数学模型。依据该模型深入分析了噪声源信号的相关系数和方差对相关输出和带宽的影响。相关系数决定了相关输出的整体形式;方差影响相关输出的主瓣和旁瓣水平,方差的增大能够有效地抑制旁瓣,使主瓣变窄,主峰变尖锐,分辨率显著提高。仿真实验验证了结论的有效性。此外,建立了在不同形式相关系数情况下噪声源信号方差与调制信号带宽的关系,方差的增大使调制信号的输出带宽增大。