Fast algorithm for a near-field synthetic aperture radar processor

A radar image can be formed by coherently integrating the backscattered fields over the measured frequency band and cross-range scan. This coherent integration can be seen as a convolution of the measured data and a focusing function, which only depends on the geometry of the measurement. Thus, by applying fast Fourier transform (FFT) techniques and computing a product in the Fourier domain one can efficiently reconstruct the target image. On the other hand, in the particular case of indoor synthetic aperture radar (SAR) measurements with the same geometry, the focusing operator must be computed just once and may be reused when processing the different datasets, reducing drastically the computing time     

Single-reference near-field calibration procedure for step-frequency ground penetrating radar

The antenna system of ground penetrating radar is usually positioned in the vicinity of the ground surface to obtain sufficient spatial resolution for detecting small targets. Therefore, received signals are subject to errors caused by unwanted reflections and coupling. A near-field calibration procedure taking into account these effects as well as antenna dispersion is presented. For practical convenience, only a metal plane is used here as a calibration standard. Calibration data are measured for a set of distances between the antenna and metal plane. The reference reflections in all positions are computed using polynomial representation of the reflected signal. Then, error coefficients are obtained by a solution of a linear system of equations in the least squares sense. Experimental verification of the proposed calibration technique demonstrated efficient removal of artefacts caused by unwanted reflections. Moreover, peaks in the radar range profile become sharper after calibration if the antenna is dispersive. Consequently, the ground response in the form of an exponential term can be effectively subtracted from the received signal. This helps to reveal and discriminate shallow underground targets obscured by strong reflection of the ground surface. Experimental examples are given to illustrate the performance of the method.     

Spherical wave near-field imaging and radar cross-sectionmeasurement

The paper presents a new inverse synthetic aperture radar (ISAR) algorithm intended for radar cross-section (RCS) imaging and measurement from scattered fields. The method, based on a spherical-wave near-field illumination of the target, overcomes the requirement for an expensive compact range facility to produce a plane wave illumination. The formulation and the implementation of the algorithm are described. Some experimental results obtained in an anechoic chamber are presented to show RCS results similar to the conventional plane wave methods     

Improvements in near-field discrimination for radar or sonar systems by the use of separate transmitting and receiving arrays

A recent letter described how the near-field discrimination of a radar or sonar could be improved by the use of multiplicative signal processing. This letter shows that similar improvements can be obtained by the use of a much simpler technique employing separate transmitting and receiving arrays.     

机载雷达便携式测试系统

机载雷达参数的测试在雷达保障中起着重要作用,为了便于进行机载雷达测试,并结合机载雷达多项参数测试的特点,设计了一款基于PXI/PXIe总线的模块化机载模型雷达便携式测试系统,并对硬件选型、设备测试功能,软件开发及软件功能设计等进行了论述,实际证明这套测试系统操作简单测试精度高,能大幅度提高工作效率且具有很强的灵活性、可靠性和可扩展性。     

MIMO雷达的近场模型DOA估计

MIMO(Multiple input multiple output)雷达为实现目标角度分集,系统的天线阵一般分布式布阵,有效孔径比较大,目标一般处于天线的近场.该文从近场DOA估计的原理出发,利用MIMO的有源特性将距离参数作为已知,建立了多输入多输出系统的近场DOA估计模型,从原理上克服了传统时延定位方法存在的多目标时延对应难题.与一般近场DOA估计需要进行距离和角度的二维搜索不同,文中方位向估计只需要角度维的一维搜索,提高了运算速度.该文给出了系统可分辨最大目标数,并在理论上分析了方位向估计的CRB.     

Infrared thermograms applied to near-field testing

Electromagnetic fields close to radiant structures can be measured quickly using an infrared camera. Examples of induced fields by wire antennas over a detection screen at distances shorter than one wavelength are presented. The measured thermograms agree with simulations that take into account heat propagation on the detection screen.     

太赫兹近场成像雷达系统误差补偿方法

太赫兹成像雷达具有合成孔径时间短、分辨力高的优点,适用于近场探测,但由于器件成熟度相对不高,雷达系统常存在较大的系统失真,会降低信号质量;同时,系统固有延时的存在会引起距离测量误差,二者均会恶化雷达成像的质量。针对系统失真和固有延时,提出了最小二乘法估计的幅相误差补偿方法和固有延时补偿方法,并给出了系统误差的测量方法。试验测试结果表明,用该方法对系统进行补偿后能有效提高图像空间分辨力,改善图像质量。     

Analysis of stratified testing for multichip module systems

A stratified technique is proposed for testing multichip module systems. Stratification in multichip modules due to the different nature and procurement of these chips is exploited for achieving a high quality-level at a saving of a significant number of tests during assembly. Unlike conventional random testing, the proposed approach (referred to as the lowest yield-stratum first-testing), takes into account the uneven known-good-yield. In the lowest yield-stratum first-testing approach, the effect of the uneven known-good-yield between strata is analyzed with respect to the variance of known-good-yield and the sample size. The lowest yield-stratum first-testing approach significantly outperforms conventional random testing and random stratified testing. This method is competitive even compared to a conventional exhaustive testing at a very small loss in quality-level by greedy (first) testing the chips in the stratum with lower known-good-yield. A Markov-chain model is developed to analyze these testing approaches under the assumption of physically independent failure of chips in multichip module systems     

Adaptive Doppler-Kalman filter for radar systems

Time-dependent Fourier transform plays an important role in radar signal analysis. The Doppler frequency carries information about the relative velocity of a moving target regarding the radar antenna. However, because the target movement may be very complex, with temporary high-intensity manoeuvres, the Doppler frequency must be estimated by using a window function. In order to minimise the estimation error, the window function width must be dependent on the target manoeuvre as well as on the signal-to-noise ratio. Here, a system consisting of a Doppler filter and a second-order Kalman filter, connected in an adaptive structure, has been proposed as an efficient solution to this problem. The proposed approach enables the window width adaptation, based on the estimates of target acceleration and signal-to-noise ratio, generated by an adaptive Kalman filter. Simulation results demonstrate the advantage of this structure compared to the fixed-width, window-based algorithms, giving acceptable results even for very bad signal-to-noise conditions.     

Image design for terrain-mapping radar systems

The theory of parameter estimation is applied to the problem of mapping radar image design. A postdetection processing technique guided by this theory yields quantitative interrelations among important final image parameters, i.e., number of grey levels of a specified confidence factor, dynamic range, and final image sample distance. In turn, it is found that specification of the foregoing places sample distance and minimum signal-to-noise (SNR) requirements on the raw radar data prior to processing. The formulas, table, and curves presented, although for an ideal terrain mapper, give insight as to the quantity of data necessary to produce terrain maps of a specified quality.     

Digital correlation for noise radar systems

A recently developed radar system using a c.w. microwave noise spectrum from an impatt oscillator as the transmitted signal has shown useful performance. The application of a digital correlator to measure, essentially in real time, the autocorrelation function of the noise spectrum and provide a radar display of targets at ranges of up to at least 1 km is now described.     

近场条件下数字阵列雷达自适应波束形成技术研究

针对近场条件下数字阵列雷达导向矢量幅相非一致性对自适应波束形成（adaptive beamforming,ADBF）算法性能的影响,通过构建近场多通道数字阵列雷达回波信号模型,分析近场多通道信号二维频谱,发现在近场条件下带限干扰信号的频谱会出现非均匀分布,呈现周期性栅格分布特征,造成算法性能下降.本文提出一种具有全新干扰样本选择策略的近场ADBF(near field ADBF, NF-ADBF)算法,通过寻优干扰信号频谱栅格边界,在栅格区间进行多门限样本筛选,离散提取干扰信号样本,构建完备的干扰信号协方差矩阵,提升近场条件下的自适应处理性能.通过在地面搭建仿真试验环境,模拟典型的数字阵列近场工作环境,通过录取试验数据分析并与理论仿真进行对比,验证了近场干扰样本筛选策略和NF-ADBF算法模型的有效性.     

Overview of an image-based technique for predicting far-field radar cross section from near-field measurements

For the last 18 years, our group has been developing a variety of near-field-to-far-field transformations (NFFFTs) for predicting the far-field (FF) RCS of targets from monostatic near-field (NF) measurements. The most practical and mature of these is based on the reflectivity approximation, commonly used in ISAR imaging to model the target scattering. This image-based NFFFT is also the most computationally efficient because - despite its theoretical underpinnings - it does not explicitly require image formation as part of its implementation. This paper presents a formulation and implementation of the image-based NFFFT that is applicable to two-dimensional (2D) spherical and one-dimensional (1D) circular near-field measurement geometries, along with numerical and experimental examples of its performance. We show that the algorithm's far-field RCS pattern-prediction performance is quite good for a variety of frequencies, near-field measurement distances, and target geometries. In addition, we show that the predicted RCS statistics remain quite accurate under conditions where the predicted far-field patterns have significantly degraded due to multiple interactions and other effect.     

Multifunctional radar systems

The paper contains data about characteristics of several radar systems designed for visualization of radar situation during surveillance of sea areas of economic regions and fishing areas, and for security purpose.     

Long microwave delay fiber-optic link for radar testing

A long fiberoptic delay line is used as a radar repeater to improve radar testing capabilities. The first known generation of 152 μs delayed ideal target at X-band (10 GHz) frequencies having the phase stability and signal-to-noise ratio (SNR) needed for testing modern high-resolution Doppler radars is demonstrated with a 31.6-km experimental externally modulated fiberoptic link with a distributed-feedback (DFB) laser. The test application, link configuration, and link testing are discussed     

Rapid near-field antenna testing via arrays of modulated scatteringprobes

Key results are summarized of efforts to significantly reduce the near-field measurement time by utilizing one- or two-dimensional arrays of modulated scattering probes in lieu of the single probe ordinarily used in conventional near-field measurement techniques. Results of analytical, numerical, and experimental investigations show that the modulated-scattering technique (MST) using arrays of hundreds or even thousands of modulated scattering probes can be used to map the complex near-field of antennas or scatterers in a few seconds or minutes. The results also strongly indicate that classical (nonmodulated) receiving/transmitting arrays can be adapted for rapid near-field data collection. Major factors affecting the accuracy and speed of probe arrays for near-field measurement are delineated and discussed. Experimental results obtained using laboratory prototype MST systems are also presented and discussed     

A microwave radar technique for dynamic testing of large structures

In this paper, the authors propose an innovative survey radar technique based on microwave holographic images for dynamic testing of large structures providing both vibration amplitude pattern and frequency. Theoretical background is provided and experimental results obtained during a dynamic test on a concrete and masonry building are reported.