Radar sensor using low probability of interception SS-FH signals

One of the best known weakness of radar sensors in defense and security applications is the necessity to radiate a signal, which can be detected by the target, so being possible (easy in fact) that the target is alerted about the presence of a radar before the radar is alerted about the presence of a target. In this context, Low Probability of Interception (LPI) Radars try to use signals that are difficult to intercept and/or identify. Spread spectrum signals are strong candidates for this application, and systems using special frequency or polyphase modulation schemes are being exploited. Frequency hopping, however, has not received much attention. The typical LPI radar at this moment of the technology is a CW-LFM radar. The simplicity of the technology is its best point. Polyphase codes, on the other hand have the inherent advantage of high instantaneous bandwidth regardless of observation time. But the complexity of the hardware is also higher. FH signals have traditionally been considered of lower performance but higher complexity, due to the difficulties to compensate the individual dopplers for the individual range cells in the receiver. One important point is that an FH radar must be clearly distinguished from an agile frequency radar. In the latter, a pulsed signal is transmitted using different frequencies from pulse to pulse. In an FH radar the frequency changes must be during the pulse. In fact, in an LPI FH radar, a CW frequency hopped signal is used. A radar system concept is proposed in which it shows how these problems can be overcome in a tracking application. Also, the signal format is analyzed under the scope of future decade digital interceptors, showing that, in fact, this kind of signal exhibits improvement in some performances and requires a hardware that is only slightly more complex than that needed for CW-LFM systems     

基于拖曳式干扰机的ISAR微动散射波干扰方法

通过对微多普勒效应的研究,提出了一种新的逆合成孔径雷达（ISAR）散射波干扰方法。将拖曳式干扰机和ISAR接收机分别等效为双基ISAR的发射站和接收站,干扰机对截获的ISAR信号进行微动信息调制并转发至目标,由其散射至ISAR接收机产生散射波干扰效果。干扰信号经ISAR接收机处理后可在真实目标回波成像结果附近产生假目标,且在方位向形成干扰条带。实验结果表明：通过控制干扰机转发参数及微动调制参数可分别实现不同的压制干扰效果。由于拖曳式干扰机与目标距离较近,干扰信号可获得较大功率,且与真实目标回波相参,可获得ISAR二维脉冲压缩处理增益,与传统射频噪声压制干扰方法相比成本较小。     

基于广义Kalman估计的机载雷达高精度控制系统

 研究了在某型现役机载雷达系统中, 采用广义Kalman 滤波器方法来预估目标机的俯仰角和方位角,产生跟踪目标用的雷达天线驱动信号, 替代传统的速率陀螺测量元件来补偿本机机动所造成的扰动的方法,同时对探测信号本身所具有的延迟起到了补偿作用。对目标的运动采用直角坐标系中的Singer 模型描述, 而对测量信号则是应用极坐标系中的描述, 采用广义Kalman 滤波器来完成估计, 即在每一步的估计和控制中对计算测量方程进行线性化结果, 实现两种坐标系的转换。通过应用Matlab/ Simulink 软件对整个系统的建模、设计及仿真研究, 得到了满意的结果。     

一种改进的FMCW SAR RD成像算法

FMCWSAR将调频连续波与合成孔径成像技术结合于一体,是一种新近被提出来的成像雷达体制,它以其体积小、重量轻、成本低、分辨率高等一系列优点,引起越来越多的关注。然而,在FMCWSAR系统中,雷达连续不断地发射信号,调制信号周期相对较长,停一走（STOP AND GO）近似不再成立,所以要用合适的算法来实现成像。针对FMCW SAR的特点,详细推导了停一走近似失效时FMCW SAR的信号模型及处理过程,提出了一种改进的RD算法。此方法是通过补偿连续运动引入的多普勒频移,消除连续运动的影响。     

Imaging of target with complicated motion using ISAR system based on IPHAF-TVA

The technique of imaging a target with a complicated motion using an Inverse Synthetic Aperture Radar (ISAR) system is an effective tool in the field of radar signal processing. After the translational compensation, the received signal reflected from the target can take the form of a multi-component Polynomial Phase Signal (m-PPS), and the high quality ISAR image can be provided via the combination between the estimated parameters of the m-PPS and the Range Instantaneous-Doppler technique (RID). For a target with a high maneuvrability, the occurrence of scatterers Migration Through Resolution Cell (MTRC), caused by the rotational movement could be appearing. That is why the variation in the amplitude of the echo during the time of observation cannot be neglected. The purpose of this study is the parameters estimation of the m-PPS signal with order three in the case of the Time Varying Amplitude (TVA). The Improved-version of the Product High-order Ambiguity Function (IPHAF) with TVA is proposed to improve the quality of the ISAR image compared with traditional techniques based on a constant amplitude; the experimental outcomes confirm that the new IPHAF-TVA method presented in this study is an effective technique to make the ISAR image very clear.     

基于滤波器结构的压缩感知雷达感知矩阵优化

 压缩感知雷达的目标场景恢复性能要求不同目标的反射回波在压缩空间上的互相关性尽可能小。基于该思想,提出了压缩感知雷达感知矩阵优化模型,根据系统参数和任务信息,以降低感知矩阵互相关性为目标,自适应地构造发射波形和测量矩阵,提升系统性能。分别给出了基于滤波器结构的压缩感知雷达发射波形优化、测量矩阵优化以及波形-测量矩阵联合优化算法。仿真结果表明:本文提出的压缩感知雷达感知矩阵优化模型和算法能够有效地提高场景恢复精度。     

SAR ATR performance using a conditionally Gaussian model

A family of conditionally Gaussian signal models for synthetic aperture radar (SAR) imagery is presented, extending a related class of models developed for high resolution radar range profiles. This signal model is robust with respect to the variations of the complex-valued radar signals due to the coherent combination of returns from scatterers as those scatterers move through relative distances on the order of a wavelength of the transmitted signal (target speckle). The target type and the relative orientations of the sensor, target, and ground plane parameterize the conditionally Gaussian model. Based upon this model, algorithms to jointly estimate both the target type and pose are developed. Performance results for both target pose estimation and target recognition are presented for publicly released data from the MSTAR program     

Hardware-in-the-loop simulation technology of wide-band radar targets based on scattering center model

Hardware-in-the-loop(HWIL) simulation technology can verify and evaluate the radar by simulating the radio frequency environment in an anechoic chamber. The HWIL simulation technology of wide-band radar targets can accurately generate wide-band radar target echo which stands for the radar target scattering characteristics and pulse modulation of radar transmitting signal. This paper analyzes the wide-band radar target scattering properties first. Since the responses of target are composed of many separate scattering centers, the target scattering characteristic is restructured by scattering centers model. Based on the scattering centers model of wide-band radar target, the wide-band radar target echo modeling and the simulation method are discussed. The wide-band radar target echo is reconstructed in real-time by convoluting the transmitting signal to the target scattering parameters. Using the digital radio frequency memory(DRFM) system,the HWIL simulation of wide-band radar target echo with high accuracy can be actualized. A typical wide-band radar target simulation is taken to demonstrate the preferable simulation effect of the reconstruction method of wide-band radar target echo. Finally, the radar target time-domain echo and high-resolution range profile(HRRP) are given. The results show that the HWIL simulation gives a high-resolution range distribution of wide-band radar target scattering centers.     

The Design of Huffman Sequences

The paper presents a method by which the zeros of the polynomial representing a Huffman (impulse-equivalent) pulse sequence can be chosen so as to exert a degree of control on the form of the energy distribution of the signal in the time-frequency plane. This makes it possible to design Huffman pulse sequences which are suitable for use as radar or sonar signals in situations where significant target velocity occurs.     

比相单脉冲雷达测角与角闪烁研究

比相单脉冲雷达采用和差通道接收信号比相的方法测角。一般认为,雷达事实上并不是在测量目标的方向,而是在测量目标的角闪烁方向。从特殊的两点目标出发,分析了单点目标和复杂目标下比相单脉冲雷达和差通道方式测角的原理与内在异同,探讨了比相单脉冲雷达测角与角闪烁的关系,提出有关雷达测角的新的观点。     

基于导航卫星反射信号的空间飞行器探测定位方法

导航卫星信号经由空间飞行器后将发生反射与散射,此信号对于飞行器自身的定位通常作为多径信号被消除。利用双基无源雷达的概念,提出利用该信号实现空间飞行器的远程定位方法。该方法充分利用空间飞行器对于导航卫星信号的反射与散射,在地面/空中设置可以接收此反射信号的接收机,从而实现飞行器的探测。接收机利用码延迟锁定环路实现直射信号与反射信号的锁定,并通过求解直射信号与反射信号的相关功率获得其路径差,进而计算出空间飞行器的位置。介绍了利用延迟映射接收机(DMR)探测空间飞行器的系统组成,并给出了远程定位的数学模型、关键技术分析、DMR的设计原理及验证实验,实验结果表明所设计的DMR可以有效地接收到导航卫星反射信号。为空间飞行器的探测提供了一种新型的手段。     

宽带信号去斜脉冲压缩处理方法的研究

宽带信号广泛应用于雷达、导航和卫星通讯等领域。宽带信号的传统接收处理方法主要是采用匹配滤波或子带分割技术。本文用去斜脉冲压缩处理方法处理宽带信号,给出了具体的实现结构和改进措施,分析了如何选择系统的信号采样频率,同时还给出了脉压波形的仿真结果及性能分析。实验表明:对中心频率为9.5GHz、带宽1.3GHz、脉冲宽度30μs的宽带线性调频信号,采用该方法处理只需90MHz采样数据率,大大降低了数据采集的难度。     

Signal-to-Noise Ratio Calculations in Pulse and Pulse Doppler Radars

In low pulse-repetition frequency (PRF) pulse radars, signal-to-noise ratio (SNR) is usually calculated on a per pulse basis and this value is then multiplied by the number of pulses integrated to obtain the SNR for a given duration of target illumination. In high PRF pulse Doppler radars, SNR is usually calculated by using the centerline power of the transmitted signal spectrum as the target return power because the centerline is kept in the receiver and returns of the PRF lines are notched out [1]. We show here that both methods of SNR calculations are entirely equivalent for matched transmit-receive radar systems.     

改进 K-均值算法在雷达辐射源信号预分选中的应用

雷达辐射源信号分选是电子对抗领域一个关键技术,随着电子技术的发展,电磁环境日趋复杂,信号分选的难度越来越大,在这样的条件下,我们应该寻求新的解决问题的方法.本文首先概述了雷达辐射源信号分选意义、系统组成和分选流程,然后介绍了改进 K-均值算法.为了有效实现信号分选,提出了基于改进K-均值算法的信号分选方法,该方法可对到达角、载频和脉宽参数进行分选.最后进行了仿真实验,结果表明该方法实现简单,分选效果较好     

雷达信号的模糊聚类分选方法

随着现代电子战的激烈对抗,复杂体制雷达迅速增加并逐渐占居主导地位,侦察接收机接收到的雷达信号更加复杂和密集.为克服传统信号分选算法的局限性,采用基于模糊聚类分析的雷达脉冲信号分选方法,此方法能利用雷达信号的特征参数有效地分选出非常规和常规雷达信号.首先介绍模糊聚类的基本原理,并进行信号分选仿真实验.仿真结果证明分选结果较理想,验证了此方法的有效性和可行性.该方法易编程实现,适用于处理大量数据,是一种解决密集复杂脉冲信号分选问题的新途径.     

Flyable fiber-optic radar target generator

Airborne radar relies on Built-in-Test (BIT) for fault detection, fault isolation and system calibration. The capability of BIT is often limited by space, weight, size and cost considerations. Furthermore, the radar does not have a test target that will allow BIT to perform in flight, closed-loop functional test of the complete radar system. This paper describes a fiber-optic based radar test target unit that provides a delayed replica of the transmitted radar signal. The unit will intercept a small amount of radar-transmitted energy, delay it in the fiber, then feed it back into the radar producing a calibrated “echo” at a predetermined radar range. The unit can be installed as part of the airborne radar. The details on the design and testing of a proof-of-concept unit are also given     

A Clutter Reduction Technique for Random Signal Radars

The performance of certain radars is degraded in environments with significant clutter returns, and since the clutter is signal-generated, increasing the transmitted power does not improve the situation. However, changing the pulse width and pulse period of the transmitted signal can increase the input signal-to-interference ratio. In this correspondence, the transmitted signal is made up of pulses of random waveforms and the receiver is a correlator where the reference signal extends over many pulses. An expression for input signal-to-interference ratio as a function of pulse width and period is obtained for the case of a distributed target. This expression could be maximized by any of several methods, but to further elucidate the clutter reduction technique, contour plots of the input signal-to-interference ratio are presented.     

Second time around radar return suppression using PRI modulation

A technique for suppressing second-time-around radar returns using pulse-repetition interval (PRI) modulation is presented and analyzed. It is shown that a staggered PRI radar system can offer considerable improvement over a nonstaggered radar system in rejecting second-time-around returns which cause false alarms. This improvement is a function of detector implementation (noncoherent integrator or binary integrator), the number of staggered PRIs, the quiescent false alarm number, the Swerling number of the false return, the transmitted signal power, the second-time-around noise power, and the quiescent noise power of the radar. Small changes in transmitted signal power can be traded off with the quiescent false alarm number to suppress the bogus return significantly. In addition, for a noncoherent integrator, all other parameters being equal, if the second-time-around return is a Swerling case II or IV target, then there is an optimum number of staggered PRIs that can be chosen to minimize the likelihood of its detection. It is also shown that the binary integrator significantly reduces the number of second-time-around return detections when compared with the noncoherent integrator. However, there is an accompanying loss of detection     

Weight effects on the periodic ambiguity function

CW radar signals and processors are discussed. The use of the periodic ambiguity function (PAF) to analyze the delay-Doppler performance of CW signals and their corresponding correlation receivers, is extended to include weight function effects. This work provides tools which can predict the delay-Doppler response of almost any phase-coded CW radar. Examples demonstrate that a combination of CW signals having perfect periodic autocorrelation, a matched reference signal with a large number of modulation periods and a smooth weight function, can create a delay-Doppler response with extremely low sidelobes, strongly resembling the response of a coherent pulse train