A COMPARISON OF SOME ELECTRONIC COUNTERMEASURES ON INVERSE SYNTHETIC APERTURE RADAR (ISAR)

Inverse Synthetic Aperture Radar (ISAR) is an important means for target classification, recognition, identification and many other military applications. A simulation model of ISAR system is established after analyzing the principle of ISAR imaging, and then several ECM (Electronic Counter Measurement) techniques are studied. Simulation experiments are done on the basis of such research. The experimental result of the research can be used for ECM equipment.

Micro-motion effect in inverse synthetic aperture radar imaging of ballistic mid-course targets

For ballistic mid-course targets,in addition to constant orbital motion,the target or any structure on the target undergoes micro-motion dynamics,such as spin,precession and tumbling.The micro-motion characteristics of the ballistic mid-course targets were discussed.The target motion model and inverse synthetic aperture radar(ISAR) imaging model for this kind of targets were built.Then,the influence of micro-motion on ISAR imaging based on the established imaging model was presented.The computer simulation to get mid-course target echoes from static darkroom electromagnetic scattering data based on the established target motion model was realized.The imaging results of computer simulation show the validity of ISAR imaging analysis for micro-motion targets.

Distributed inverse synthetic aperture radar imaging of ship target with complex motion

For ship targets with complex motion,it is difficult for the traditional monostatic inverse synthetic aperture radar(ISAR)imaging to improve the cross-range resolution by increasing of accumulation time.In this paper,a distributed ISAR imaging algorithm is proposed to improve the cross-range resolution for the ship target.Multiple stations are used to observe the target in a short time,thereby the effect of incoherence caused by the complex motion of the ship can be reduced.The signal model of ship target with three-dimensional(3-D)rotation is constructed firstly.Then detailed analysis about the improvement of crossrange resolution is presented.Afterward,we propose the methods of parameters estimation to solve the problem of the overlap or gap,which will cause a loss of resolution and is necessary for subsequent processing.Besides,the compressed sensing(CS)method is applied to reconstruct the echoes with gaps.Finally,numerical simulations are presented to verify the effectiveness and the robustness of the proposed algorithm.

Improved chirp scaling algorithm integrated motion compensation for parallel-track bistatic synthetic aperture radar

To compensate motion errors of images from the parallel-track bistatic synthetic aperture radar（BiSAR）,an improved chirp scaling algorithm（CSA） is proposed.Since velocity vector of the moving aircrafts in the parallel-track BiSAR system can not remain invariant in an aperture,an actual aperture is divided into subapertures so that it is reasonable to assume that the aircrafts move with constant acceleration vector in a subaperture.Based on this model,an improved CSA is derived.The new phase factors incorporate three-dimensional acceleration and velocity.The motion compensation procedure is integrated into the CSA without additional operation required.The simulation results show that the presented algorithm can efficiently resolve motion compensation for parallel-track BiSAR.

Spatial Channel Sounding Based on Bistatic Synthetic Aperture Radar Principles

In this paper, we propose a simplified spatial channel sounding method by utilizing bistatic synthetic aperture radar(BiSAR) principles. Despite the different deployment geometries compared with a conventional BiSAR system, the feasibility of the approach is established by 1) the proposed method achieves a better spatial resolution than conventional directional channel sounders and 2) reconstruction algorithms based on time-domain backprojection in conjunction with a digital elevation model provide a good imaging performance and are suitable for reconstructing the spatial distribution of scatterers. Simulations of a high-speed rail(HSR) scenario demonstrate that the estimated power delay profiles(PDPs) and power angle profiles(PAPs) are close to the actual values.

Inverse synthetic aperture radar range profile compensation of plasma-sheath-enveloped reentry object

The scattering points in a plasma sheath characterized with coupled velocities can cause pulse compression mismatching,which results in displacement and energy diffusion in the onedimension range profile.To solve this problem,we deduce the echo model of the plasma-sheathenveloped reentry object.By estimating the coupled velocities,we propose a compensation method to correct the defocus of an inverse synthetic aperture radar(ISAR)image in range dimension to improve the quality of the ISAR images.The simulation results suggest that the echoes from different regions of the surface of the reentry object have various coupling velocities,and the higher the coupled velocity,the more serious the displacement and energy diffusion in the range dimension.Our proposed method can correct the range dimension aberration.Two measurement metrics were used to evaluate the improvement of the compensation method.

New Precision Guidance Method Based on Bistatic Synthetic Apterture Radar

A new method is presented to improve guidance precision. This method is based on bistatic synthetic aperture radar. The illuminator works in side looking mode, providing the synthetic aperture and the receiver is disposed on the seeker which operates in the forward looking mode. The receiving antenna is composed of four sub-antennas and so four synthetic aperture radar （SAR） images are to be generated. Target is positioned in SAR images by image matching. The bearing and elevation of image element of target are measured by the principle of monopulse angular measurement. Theory of the proposed method is derived and simulation on bearing measurement is done. Simulation shows that the method is valid and if SNR of target＇s image is above 30 dB, the angular measuring difference is within the confines of 0.04 degree.

一种联合TDCM和PFA的空间目标大转角ISAR成像方法

空间目标态势感知是当前航天技术领域的研究热点,逆合成孔径雷达(Inverse Synthetic Aperture Radar, ISAR)是空间目标感知的一种有效手段。为了得到利于目标鉴别的高分辨二维ISAR图像,需要通过增大积累转角来提高方位向分辨率。但是,随着转角的增大,平动与转动之间的耦合增大,使得传统的先平动补偿、后利用转动成像的两步式成像方法不再适用。本文提出了一种结合时域信号共轭相乘(Time Domain Conjugate Multiplication, TDCM)处理与极坐标格式算法(Polar Format Algorithm, PFA)的成像算法,首先利用雷达回波的二维相干性,通过TDCM处理进行平动粗补偿,然后借助PFA的插值操作校正大转角引起的散射点越分辨单元走动(Motion Through Resolution Cell, MTRC)并估计目标相对转动参数。通过迭代处理,持续对平动和转动参数进行优化,提升运动补偿效果。仿真验证了所提成像算法的有效性,与传统算法相比,成像聚焦性更好。

空间目标ISAR图像三维基元表示方法

空间卫星目标的逆合成孔径雷达(ISAR)图像由离散的散射点构成,具有弱纹理、高动态、非连续的特性,造成传统算法对空间目标ISAR图像进行三维重建时,得到的点云结果稀疏,无法覆盖目标整体外形轮廓,进而导致难以精确提取目标结构、姿态参数。针对上述问题,并考虑到空间目标通常由特定模块化部件组成的特点,该文提出一种从空间目标ISAR图像中抽取参数化基元来表示其三维结构的方法。首先利用能量累积算法从ISAR图像中得到目标的稀疏点云,进而利用参数化基元对点云进行拟合,最后将基元投影至ISAR成像平面,并最大化与目标图像的相似度来优化基元参数,得到最优的目标三维基元表示。相比于传统点云三维重建,该方法能够获得对目标三维结构更完整的描述,且所得到的基元参数即代表目标的姿态及结构,可直接支撑后续的目标识别、分析研判等任务。仿真实验证明该方法能够根据ISAR序列图像,有效实现对空间目标的三维表示。

结合最近邻图模型的稀疏ISAR成像方法

逆合成孔径雷达(Inverse Synthetic Aperture Radar,ISAR)稀疏成像方法可提供图像对比度高、旁瓣干扰少的成像结果 .稀疏成像以场景或目标散射率分布具有稀疏性为前提,待成像目标场景的稀疏特性决定了最终成像质量. ISAR目标场景的自然稀疏特性着重刻画点状特征,变换域稀疏表示可增强目标图像的纹理等通用特征.通过学习获得的稀疏变换字典,可自适应于待成像的ISAR目标场景,找到面向ISAR目标图像块的特有稀疏表示.但是,图像块的特有稀疏表示中忽略了待成像目标场景中目标的几何特征信息.最近邻图模型可建立给定数据的几何特征描述算子,刻画出给定数据的几何特征信息.本文利用最近邻图模型来刻画待成像目标场景中目标的几何特征信息,并映射到待成像目标场景的特有稀疏表示中;提出结合最近邻图模型的ISAR稀疏成像方法,用于不同类别实测ISAR数据成像.相比已有的ISAR稀疏成像方法,所提成像方法可获得目标轮廓更清晰的成像结果,成像所需时间平均减少10.4%.

False-target image synthesizer for countering ISAR via inverse dechirping

For real-time jamming signal generation in deceiving inverse synthetic aperture radar（ISAR）,the target characteristics modulation is always processed in the expensive field programmable gate array（FPGA）.Due to the large computational complexity of the traditional modulating operation,the size and structure of simulated false-target are limited.With regard to the principle of dechirping in range compression of linear frequency modulated（LFM） radar,a novel algorithm named ＂inverse dechirping＂ is proposed for target characteristics modulation.This algorithm only needs one complex multiplier in the FPGA to generate the jamming signal when the radar signal is intercepted,which can be obtained by multiplication of radar signal samplings and the equivalent dechirped target echo in the time domain.As the complex synthesis of dechirped target echo can be realized by cheap digital signal processor（DSP） within the interpulse time,the overall cost of the jamming equipment will be reduced and the false-target size will not be limited by the scale of FPGA.Numerical simulations are performed to verify the correctness and effectiveness of the proposed algorithm.

基于Multitask⁃YOLO网络的卫星帆板ISAR图像快速分割

随着空间技术的飞速发展,空间态势感知能力需求不断增加。与传统光学传感器相比,逆合成孔径雷达(Inverse synthetic aperture radar,ISAR)具有全天候、远距离高分辨率成像的能力,且成像不受光照条件的影响。此外,空间态势感知系统需要对周围航天器进行准确的评估,因此对空间目标部件识别能力的需求日益迫切。本文提出了一种基于YOLOv5结构的Multitask⁃YOLO网络,用于卫星ISAR图像中卫星帆板的识别和分割。首先,本文添加了分割解耦头来实现网络的分割功能。然后用空间金字塔池快速算法(Spatial pyramid pooling fast,SPPF)和距离交并比算法(Distance intersection over union,DIoU)代替原有结构,避免图像失真,加快收敛速度。通过在通道中引入注意机制,提高了分割和识别的准确性。最后使用模拟卫星的ISAR图像进行实验。结果表明,所提出的Multitask⁃YOLO网络高效、准确地实现了部件的识别和分割。与其他的识别和分割网络相比,该网络的平均精度(mean Average precision,mAP)和平均交并比(mean Intersection over union,mIoU)提高了约5%。此外,该网络的运行速度高达16.4 GFLOP,优于传统的多任务网络的性能。

Multi-static InISAR imaging for ships under sparse aperture

This paper concentrates on super-resolution imaging of the ship target under the sparse aperture situation.Firstly,a multi-static configuration is utilized to solve the coherent processing interval(CPI)problem caused by the slow-speed motion of ship targets.Then,we realize signal restoration and image reconstruction with the alternating direction method of multipliers(ADMM).Furthermore,we adopt the interferometric technique to produce the three-dimensional(3D)images of ship targets,namely interferometric inverse synthetic aperture radar(InISAR)imaging.Experiments based on the simulated data are utilized to verify the validity of the proposed method.

基于某ISAR的压制干扰效果分析

逆合成孔径雷达(ISAR)作为高分辨率微波成像雷达,已经广泛应用于目标识别及精确制导。为更有效地保护目标,对于ISAR干扰的研究已成为重要的研究课题,在常见干扰方式上,对于ISAR干扰效果的评估显得尤为重要。分析常见的4种ISAR噪声压制干扰的干信比临界点,得出结论性数据,为工程应用提供有效干扰ISAR的干信比(JSR)参考门限。

Compressive Sensing Inverse Synthetic Aperture Radar Imaging Based on Gini Index Regularization

In compressive sensing(CS) based inverse synthetic aperture radar(ISAR) imaging approaches, the quality of final image significantly depends on the number of measurements and the noise level. In this paper, we propose an improved version of CSbased method for inverse synthetic aperture radar(ISAR) imaging. Different from the traditional l1 norm based CS ISAR imaging method, our method explores the use of Gini index to measure the sparsity of ISAR images to improve the imaging quality. Instead of simultaneous perturbation stochastic approximation(SPSA), we use weighted l1 norm as the surrogate functional and successfully develop an iteratively re-weighted algorithm to reconstruct ISAR images from compressed echo samples. Experimental results show that our approach significantly reduces the number of measurements needed for exact reconstruction and effectively suppresses the noise. Both the peak sidelobe ratio(PSLR) and the reconstruction relative error(RE) indicate that the proposed method outperforms the l1 norm based method.

A new autofocus method for inverse synthetic aperture radar——Local dominant scatterer synthesis

Motion compensation is a key and difficult step in inverse synthetic aperture radar (ISAR) . The calibration of initial phase errors, which is well known as autofocus, requires very high precision, so it determines the quality of the reconstructed image to a great extent. A new autofocus method called the local dominant scatterer synthesis (LDSS) is presented. It has the capability to sufficiently reduce the errors induced by clutter and noise, and the advantage of having wide applications. Experiments of real measured data have shown its effectiveness.

Focusing Azimuth-Invariant Bistatic Synthetic Aperture Radar Data Based on a Polynomial Model

In this paper,a focusing approach is presented to widen the use of efficient monostatic imaging algorithms for azimuth-invariant bistatic synthetic aperture radar(SAR) data.The bistatic range history is modeled by a polynomial of azimuth time.Using this model,an analytic form of the signal spectrum in the 2D frequency domain is derived,and a simple single-valued relation between the transmitter and receive ranges is established.In this way,a lot of monostatic image formation algorithms can be extended for the bistatic SAR data,and a bistatic chirp scaling algorithm is developed as an application of the new approach.This algorithm can be used to process the azimuth-invariant bistatic configuration where the transmitter and receiver platforms are moving on parallel tracks with the same velocity.In addition,some simulation results are given to demonstrate the validity of the proposed approach.

Doppler Properties of Spaceborne/Airborne Hybrid Bistatic Synthetic Aperture Radar

In this paper,a special geometry case of spaceborne-airborne bistatic SAR(SA-BiSAR) is considered,in which satellite and aircraft flight paths are parallel and their antennas are steering at the strip map.This case is a simple but typical application example,which is applicable for non-cooperative illumination.The integration time of SA-BiSAR system is derived via the motion of transmitter and receiver footprint.In parallel and stripmap mode,Doppler frequency is obtained through the combination be-tween spaceborne and airborne SAR.Other Doppler properties have been envisaged,including Doppler bandwidth and azimuth resolution.The overall simulation experiments are conducted and some characteristics are exhibited.The critical parameters,which have the significant effect on the SA-BiSAR Doppler properties,are extracted by analytical expressions and numerical simulations.In parallel and strip map mode and with reference to ENVISAT-1,SA-BiSAR system possesses the potential of yielding 10 m azi-muth resolution and 0.5 s integration time for C-band via the analysis of simulation results.

A jamming method against bistatic SAR based on modulation theory

This paper focuses on the jamming problem of bistatic synthetic aperture radar (BiSAR), and a jamming method against BiSAR based on modulation theory is proposed. The proposed jamming method modulates the BiSAR signal with the cosinusoidal phase to generate multi-false targets in range, and further rotates the jammer to generate multi-false targets in azimuth. The range multi-false targets and azimuth multi-false targets form the two-dimensional cover jamming or deception jamming, which can protect the important targets efficiently. The number of false targets, the interval of false targets, and the jamming square can be adjusted flexibly by setting different range jamming parameters and azimuth jamming parameters. The jamming performance and the choosing criteria of jamming parameters are also discussed. Finally, the simulated data verify the effectiveness of the jamming method.

RESEARCH ON THE BISTATIC FORWARD-LOOKING SAR IMAGING

The bistatic Synthetic Aperture Radar (SAR) systems with separate transmitter and receiver antennas provide a new potential to imaging in the forward-looking geometry. Analysis of the Doppler property in this paper indicates the feasibility of Bistatic Forward-Looking (BFL) SAR imaging. Considering the different Doppler property determined by the two platforms in BFL SAR, a new 2-D point target spectrum is derived in our study. Based on the spectrum, an imaging method is chosen for the configuration, and the point target simulation validates the analysis.