New approach for ISAR imaging of ship target with 3D rotation

Inverse synthetic aperture radar (ISAR) imaging of ship target is very important in the national defense. The imaging condition for ship target is very complicated due to the complexity of the ship’s movement, and a three-dimensional (3D) rotation occurs for the ship with the oceanic waves. Furthermore, the multi-path effect can not be avoided in most circumstance. In general, the received signal for a 3D rotation ship target can be characterized as multi-component polynomial phase signals (PPS), and the parametric method can be used to obtain the instantaneous ISAR images. In this paper, the received signal is considered as multi-component cubic phase signal, and a new method for ISAR imaging of ship target with 3D rotation by the product high order bilinear matched-phase transform (PHBMT) is proposed. The instantaneous ISAR image is obtained, and the multi-path effect can be eliminated by separating the ISAR image in the range-instantaneous-Doppler domain. Results of real data validate the effectiveness of the new approach presented.     

用于空间转换的巴克ISAR信号形成与图像重构

讨论了基于巴克相位编码调制发射信号和三维逆合成孔径雷达（ISAR）结构的ISAR概念。ISAR信号形成可理解为3D图像功能向2D信号功能的非对称空间转换,而图像重构被认为是2D信号功能向2D图像功能（重构的图像）的空间逆转换。经证实,这种图像重构算法由距离压缩互相关、方位压缩傅里叶变换（被认为是第一级运动补偿）和更高级相位校正组成（被认为是更高级运动补偿,通称自聚焦程序）。引入熵作为图像成本功能,以评估相位校正功能的多项式系数。通过数值实验以验证ISAR的几何结构,信号形成模式和图像重构算法。     

有色噪声中谐波频率的频域非线性预滤波估计方法

基于谐波信号表现为频域中的 异常点 这一思路,利用滑动中值滤波器滤除数据异常点的能力,本文提出了未知有色噪声背景下谐波信号频率的一种高分辨估计方法.其突出特点是对噪声分布的强普适性,且算法实现简单.仿真结果验证了该方法的性能.     

A fast algorithm for estimating the parameters of a quadratic FM signal

This paper describes a fast algorithm that can be used for estimating the parameters of a quadratic frequency modulated (FM) signal. The proposed algorithm is fast in that it requires only one-dimensional (1-D) maximizations. The optimal maximum likelihood method, by contrast, requires a three-dimensional (3-D) maximization, which can only be realized with an exhaustive 3-D grid search. Asymptotic statistical results are derived for all the estimated parameters. The amplitude estimate is seen to be optimal, whereas the phase parameters are, in general, suboptimal. Of the four phase parameter estimates, two approach optimality as the signal-to-noise ratio (SNR) tends to infinity. The other two have mean-square errors that are within 50% of the theoretical lower bounds for high SNR. Simulations are provided to support the theoretical results. Extensions to multiple components and higher order FM signals are also discussed.     

Three-dimensional scattering center extraction using the shootingand bouncing ray technique

We present a technique to extract the three-dimensional (3-D) scattering center model of a complex target. Using the shooting and bouncing ray technique, we first generate the 3-D inverse synthetic aperture radar (ISAR) image of the target based on a one-look ISAR algorithm. In step two, we use the image processing algorithm CLEAN to extract the 3-D position and strength of the scattering centers from the 3-D ISAR image. Various implementation issues related to computation time and memory are addressed and an efficient scheme is presented to accomplish the 3-D scattering center extraction. Several examples ranging from simple canonical structures to complex targets are presented to demonstrate the validity of the extraction scheme and the usefulness of the resulting 3-D scattering center model     

基于稀疏孔径的联合稀疏约束干涉ISAR机动目标三维成像

InISAR系统能够实现对目标的3维几何估计,更加有利于目标的分类和识别。同时多功能ISAR/InISAR系统针对的多是机动性很强的目标,在某些情况下对单个目标仅能获取稀疏孔径观测,尤其是在目标存在机动特性的情况下,更是增加了ISAR成像的难度,这些对传统的ISAR成像算法提出了挑战。为了解决上述这些问题,该文针对机动目标提出一种基于稀疏孔径的联合稀疏约束InISAR 3维成像方法。对匀加速转动的目标,回波的多普勒调制可以建模成线性调频的形式,并用chirp-傅里叶字典来表征其机动性。接着将联合的多通道InISAR 2维成像转化为联合稀疏约束的最优化求解问题,并用改进的OMP算法进行求解。然后利用各个通道估计的ISAR图像和调频参数实现对目标的3维几何重构。相比于单通道独立成像,联合多通道稀疏约束成像能获得更好的2维和3维成像结果。最后,进行实测数据实验以验证该文算法的有效性。     

一种新的信号分解算法及其在机动 目标ISAR成像中的应用

本文首先提出一种新的信号分解算法——修正自适应Chirplet分解算法,将Chirplet基函数推广到非线性调频信号的形式,克服了传统自适应Chirplet分解对复杂信号逼近程度不高的缺点.然后提出单分量基函数参数估计的一种实用算法和基于CLEAN思想的多分量信号分解方法,并将其应用于机动目标的ISAR成像中,进一步提高了成像质量,外场实测数据成像结果验证了本文方法的有效性.     

一种复杂运动目标的ISAR成像算法

在对复杂运动目标进行逆合成孔径雷达成像时,由于转动矢量随时间而变化,回波信号中会引入一个与散射点位置有关的相位误差,无法用通常的相位补偿方法进行校正,应用距离-多普勒算法获得的ISAR(Inverse Synthetic Aperture Radar)像会变得模糊.本文分析了目标转动矢量变化使得ISAR像模糊的内在原因,给出了目标三维转动状态下的ISAR信号形式,并基于散射点信号的特点提出了一种复杂运动目标的ISAR成像算法.该算法不仅适用于转动矢量方向不变的非均匀转动目标,而且对于转动矢量方向缓慢变化的目标,算法仍然能够有效地提高ISAR成像的质量.仿真试验结果表明了该算法的有效性.     

Distortion in polar modulated CMOS RF power amplifiers

Polar modulation of a switching RF amplifier is an excellent candidate to combine both linearity, efficiency and CMOS integration for RF power amplifiers used in mobile and wireless communication systems. In this paper, the different sources of distortion associated with polar modulation are discussed and verified by measurement results. A fully integrated linearized CMOS RF Power Amplifier for GSM–EDGE, realized in a 0.18 μm CMOS technology, is used as a benchmark to validate the presented theory. It is demonstrated how the combination of a differential delay between the amplitude signal and the phase signal, together with the AM–PM distortion of the Class E amplifier, generates an asymmetry in the output spectrum. The effect of low-pass filtering of the envelope signal is investigated and the degradation on the linearity with and without delay adjustment is given.     

一种高精度的ISAR转动补偿和方位定标方法

传统逆合成孔径雷达(ISAR)成像算法忽略了目标回波的高阶转动相位的影响,导致方位向聚焦效果较差,且无法直接从目标图像中获取目标尺寸信息。该文提出一种转动补偿和方位定标方法。该方法采用回波的全部方位信息,通过构造局部平均多普勒趋势(LADT)信号获取目标回波的多普勒变化趋势。进一步利用随机采样一致(RANSAC)算法估计多普勒调频率及目标有效转动速度,实现高精度转动补偿与方位定标。仿真与实测数据实验验证了该方法的有效性。     

Two-dimensional ISAR model and image reconstruction with stepped frequency-modulated signal

A two-dimensional (2-D) inverse synthetic aperture radar (ISAR) return signal model that employs stepped frequency (SF) modulation is developed. The geometry of the examined ISAR scenario is described by analytical geometrical equations. The target to be imaged is represented by a rectangular grid of point scatterers, moving along a rectilinear trajectory at constant speed, without any rotational motion. Thus, the inverse synthetic aperture results from the translational motion of the target for a short period of time. The process of ISAR signal modelling through coherent summation of the SF-modulated signals reflected from different point scatterers of the target is thoroughly described. Moreover, an efficient ISAR image reconstruction approach, including cross-correlation-based range compression and fast-Fourier-transform-based azimuth compression, is presented through analytical mathematical expressions. Numerical simulations are carried out for various SF ISAR scenarios and high-resolution ISAR images are obtained by applying the proposed ISAR image reconstruction approach. Simulation results (ISAR images and corresponding entropy values) indicate the validity of the proposed 2-D SF ISAR return signal model and the efficiency of the proposed imaging algorithms. Finally, a numerical simulation result is illustrated, which shows the comparison of the performance of the proposed ISAR image reconstruction algorithms based on SF and linear frequency modulation waveforms. It is shown that the two waveforms attain almost the same ISAR image resolution.     

混沌噪声调频信号对UWB—SAR／ISAR成像的干扰

建立了n-Way Bernoulli混沌调频信号模型,分析了UWB-SAR/ISAR的成像特点,提出利用Bernoulli混沌噪声调频信号对UWB-SAR/ISAR进行成像干扰。仿真结果表明,利用Bernoulli混沌噪声调频信号干扰UWB-SAR/ISAR是可行的。     

ISAR imaging of target with complex motion based on novel approach for the parameters estimation of multi-component cubic phase signal

Inverse synthetic aperture radar (ISAR) imaging of target with complex motion is very important in the radar signal processing domain. In this case, the received signal can be characterized as multi-component cubic phase signal (CPS), and the high quality instantaneous ISAR images can be obtained by the parameters estimation approach. The match Fourier transform (MFT) has been proposed for the parameters estimation of linear frequency modulated (LFM) signal, and it has been used successfully in the field of ISAR imaging. In this paper, the third-order match Fourier transform (TMFT) is proposed as an extension of the traditional MFT for the parameters estimation of cubic phase signal, and the asymptotic statistical performance is analyzed theoretically with the derivation of asymptotic statistical results for the estimated parameters. Finally, the TMFT algorithm is used as a tool for the improvement of inverse synthetic aperture radar (ISAR) images quality of target with complex motion, and the results of simulated and real data validate the effectiveness of the TMFT algorithm.     

基于散射点信号特性的ISAR成像时间选择算法

在舰船目标ISAR成像中,在有些相关成像时间内,海浪的作用会使得舰船目标具有俯仰、偏航和滚动的三维转动,目标的ISAR像变得模糊。为获得聚焦的ISAR像,需要合理地选择成像时间,使得在相关成像时间内,目标仅具有二维转动。本文提出了一种成像时间选择的算法,该算法利用离散调频傅立叶变换估计散射点信号的参数,并根据二维和三维转动引起目标散射点信号特性的不同,推断目标的运动状态,选择成像时间。算法中有效利用了多个散射点的信息,但不要求跟踪目标特定位置上的散射点。文中还分析了算法估计的性能,并通过仿真试验证实了该算法的有效性。     

基于正弦调相的ISAR干扰方法

为了实现对ISAR干扰,本文从目标一维距离像及ISAR运动补偿的角度,提出了基于正弦调相的ISAR干扰方法。文中对干扰信号如何影响距离像、影响运动补偿进行了详细的理论分析,给出了干扰造成ISAR图像失真的理论依据。并进行了基于实测数据的仿真实验。结果表明,基于正弦调相的ISAR干扰方法可以较好地干扰ISAR的一维距离像和最终的二维像,并具有压制干扰和类似欺骗干扰的双重效果,是一种对付ISAR的有效干扰手段。     

调频信号数字解调算法的改进与实现

介绍了一种调频离散信号无盲区解调算法,以适应各种载波下调频离散信号的变频和解调。首先获取数字载波,然后对频谱进行分析以获得完整信号频谱,再进行数字变频以获得多相滤波正交解调条件,最后通过二阶数字差分算法,从而实现调制信号的无失真解调。试验结果表明：该算法解决了调频信号解调时遇盲区无法解调的情况,实现调频离散信号无盲区数字解调,提高了频谱利用率。     

Radar imaging for targets with complex rotation based on phase history decomposition

Traditional inverse synthetic aperture radar (ISAR) imaging algorithms can not obtain focused images when the target undergoes complex three-dimensional (3D) rotation. An imaging algorithm to obtain two dimensional (2D) images or 3D distributions of scattering centers is proposed in this paper for targets undergoing complex rotation in a small angular extent. Firstly, the phase histories of different scattering centers are extracted by signal decomposition and they are arranged into a phase history matrix. Then, the singular value decomposition is carried out for the phase matrix to reveal the rotation characters. 3D rotations and 2D rotations are identified from the singular values and these two cases are treated separately. When target undergoes 2D rotation, the focused ISAR image can be obtained by resampling the received signals according to the first column of the right singular matrix. When target undergoes 3D rotation, the distorted 3D scattering center model can be obtained directly from the first and second columns of the left singular matrix. The distortion and ambiguity for the extracted 3D scattering center model are also analyzed theoretically. Simulations and experimental results verify the effectiveness of the algorithm.     

基于非线性流形学习的ISAR目标识别研究

详细分析了逆合成孔径雷达（Inverse Synthetic Aperture Radar, ISAR）二维像的非线性流形结构特点,指出ISAR二维像可以看作是由位置、姿态和尺度等内在参数共同作用而张成的一个在高维图像空间中的非线性流形。在此基础上,论文将非线性流形学习的思想引入到ISAR目标识别领域,提出了一种基于局部保持投影（Locality Preserving Projections, LPP）算法和k近邻分类器的ISAR二维像特征提取和目标识别方法。该方法首先利用LPP算法对维数较高的ISAR二维像进行降维,然后采用具有拒识功能的k近邻分类器对四类飞机目标进行了分类识别。仿真实验结果表明,LPP算法能够发现嵌入在高维ISAR图像空间中的低维非线性流形,并且能够利用LPP算法降维后的特征获得较高的识别率。     

基于GRECO的复杂目标ISAR图像仿真

提出一种与图形电磁计算方法相结合的1SAR图像实时仿真方法.利用图形电磁计算(GRECO)方法得到运动目标的电磁散射数据,通过发射线性调频信号得到运动目标的雷达回波,并对仿真回波进行ISAR成像处理.与传统采用点目标仿真不同,该文是对实际三维目标直接仿真成像,更加接近实际,更加适合应用与成像效果分析、算法改进和抗干扰方面的研究.对于目标表面散射场的分析,是基于高频预估理论:采用物理光学(PO)法与物理绕射理论(PTD)来进行计算.从对复杂目标的仿真结果来看,该方法是准确有效且具有实时性的.     

ISAR Imaging of Maneuvering Targets Based on the Range Centroid Doppler Technique

A new inverse synthetic aperture radar (ISAR) imaging approach is presented for application in situations where the maneuverability of noncooperative target is not too severe and the Doppler variation of subechoes from scatterers can be approximated as a first-order polynomial. The proposed algorithm is referred to as the range centroid Doppler (RCD) ISAR imaging technique and is based on the stretch Keystone-Wigner transform (SKWT). The SKWT introduces a stretch weight factor containing a range of chirp rate into the autocorrelation function of each cross-range profile and uses a 1-D interpolation of the phase history which we call stretch keystone formatting. The processing simultaneously eliminates the effects of linear frequency migration for all signal components regardless of their unknown chirp rate in time-frequency plane, but not for the noise or for the cross terms. By utilizing this novel technique, clear ISAR imaging can be achieved for maneuvering targets without an exhaustive search procedure for the motion parameters. Performance comparison is carried out to evaluate the improvement of the RCD technique versus other methods such as the conventional range Doppler (RD) technique, the range instantaneous Doppler (RID) technique, and adaptive joint time-frequency (AJTF) technique. Examples provided demonstrate the effectiveness of the RCD technique with both simulated and experimental ISAR data.