Synthetic aperture beamformer for imaging through a dielectric wall

A coarray-based aperture synthesis scheme using subarrays and postdata acquisition beamforming is presented for through-the-wall wideband microwave imaging applications. The wall causes wave refraction and a change in the propagation speed, both effects alter the travel time between the transmitter, the target, and the receiver. Coherent combining of the pulse waveforms emitted by the different transmitters and incident at the receivers through reflections from targets and clutter requires incorporation of wall effects into the beamformer design. Simulation results verifying the proposed synthetic aperture technique for a through-the-wall imaging (TWI) system are presented. The impact of the wall ambiguities or incorrect estimates of the wall parameters, such as thickness and dielectric constant, on performance is considered.     

介质材料对频率选择表面传输特性的影响

通过理论计算和实验验证分析了介质材料对频率选择表面传输特性的影响规律,讨论了蒙皮的厚度、介电常数,芯层厚度、介电常数四个因素对FSS的通带位置、宽度、损耗的影响。结果表明,蒙皮和芯层厚度增厚会使通带位置向低频移动,厚度减小通带位置向高频移动;蒙皮和芯层介电增大会使通带位置向低频移动,介电减小通带位置向高频移动。并测试了同样结构的FSS平板传输特性,理论分析和实验结果一致性较好。     

Bayesian Detection of Targets of Unknown Location

In this paper the array detection problem for certain deterministic signals in spatially uncorrelated Gaussian noise is formulated in Bayesian terms and the required likelihood ratios and resulting performance characteristics are obtained. Primary emphasis is on detection of targets of unknown spatial location using a likelihood ratio approach, with the target location treated as a random parameter, rather than an estimator-correlator approach. The tradeoff among array parameters and signal parameters is demonstrated. It is shown that the dominant uncertainty affecting detection performance seems to be that of location when compared with uncertainty on energy and/or phase.     

一种多点定位的目标位置精确解算方法

多点定位是民航飞机导航系统的新技术,精确的目标位置解算方法是多点定位的关键.通过设定参考站和变换,将非线性到达时间(TOA)方程组转化为线性到在时间差(TDOA)方程组,提出了一种两步求解目标位置的闭式算法.首先忽略TDOA测量误差,获得了目标位置的粗解,在粗解的基础上做泰勒级数展开,克服了未知量不独立对精度的影响,再...     

Two low-cost phased arrays

In a phased array antenna, the phase shifters (or T/R modules in an active aperture phased array) with their beam-steering control circuitry along with the feed network account for the major hardware cost. This paper presents two antenna array configurations that use simpler feed, simpler phase-shifting and simpler beam-steering control circuitry for realizing low-cost phased arrays. Both are lens configurations. The first one uses a Radant lens, which provides a medium that is loaded with diodes and provides the needed phase shift by switching the diodes on and off. The other configuration employs a ferroelectric dielectric material whose dielectric constant can be varied with an applied DC bias voltage. It is shown that the ferroelectric lens may have further advantages of smaller thickness, simpler beam-steering controls and lower cost     

Application of Recursive Estimation and Kalman Filtering to Doppler Tracking

The techniques of recursive estimation and Kalman filtering are applied to the problem of estimation of space vehicle orbits and trajectories using only measurements of the Doppler shifts in radio signals transmitted by or reflected from the target. Two approaches are described. One is a global fit technique in which the parameters of an assumed trajectory model are estimated. The second is a pointwise mapping technique in which the trajectory estimate is extrapolated as the target tracking data is received. The paper provides a tutorial illustration of the direct application of recursive optimization techniques to a class of engineering problems.     

真实爆震载荷作用下爆震室等寿命设计方法

结合内径为60mm的等壁厚爆震室，建立其有限元模型并施加真实爆震载荷，确定其疲劳载荷谱类型为周期性常幅谱。通过有限元模型和静态载荷作用下的解析模型分析得出爆震室壁厚和动力放大系数之间的相互影响关系，壁厚通过动力放大系数对自身进行调整，该过程中内壁的等效应力最大值逼近目标应力，以此为基础提出爆震室等寿命设计方法。根据计算结果设计加工变壁厚爆震室试验段，通过试验测量变壁厚爆震室外壁3个测点的应变，并估算3个测点内壁处的疲劳寿命，发现3个疲劳寿命最大误差为8.82%，考虑到试验与数值计算的工况误差可认为3个测点处寿命相同，验证了爆震室等寿命设计方法的正确性。      

基于二维线阵和空间滤波器的结构冲击无波速定位方法

复合材料在航空结构中的应用越来越广,但其遭受外界物体冲击后很容易在内部产生表面不可见损伤,所以对复合材料结构的冲击事件进行在线监测十分必要。基于压电传感器（PTZ）和Lamb波的冲击定位方法是目前的研究热点,但是Lamb波信号在复合材料结构中传播的各向异性给冲击定位带来了困难。本文将空间滤波器算法推广到复合材料结构的冲击监测应用中,研究了与波速无关的空间滤波器冲击定位原理,提出了基于二维线性压电传感器阵列和空间滤波器的结构冲击无波速定位方法。该方法首先采用Shannon连续复数小波变换提取并构建宽带冲击响应信号中的窄带Lamb波解析信号;然后利用波速无关的空间滤波器算法计算出结构冲击相对于各条线性压电传感器阵列的角度;最后使用冲击无波速定位公式计算出结构冲击的位置坐标。在碳纤维层合板上对该方法进行了实验验证。验证结果表明：该方法可以实现对复合材料结构的冲击进行不依赖信号传播速度的定位,定位误差小于1 cm。     

电容近感探测目标多样性研究

基于探测器探测目标的多样性,从静电场出发,对极间电位移和电场强度特性进行了研究,进而分析了极问电容变化的本质并进行仿真。仿真结果表明目标切割电力线长度和目标相对电容率是影响极间电容变化的两个重要目标参数,目标切割电力线越长,极间电容变化越大;目标相对电容率对极间电容变化的影响很小,与Marconi公司实测的电容探测器炸高散布小的结论一致。     

压电风扇激励非定常流动和换热特性数值研究

 利用动网格技术对压电谐振风扇产生的非定常流场进行了数值模拟,以期进一步揭示压电风扇的流场特征和换热特性。研究表明:压电风扇上下两个区域均出现涡流,涡向相反(压电风扇上方为逆时针,下方为顺时针),涡对的尺度、位置和扰动范围随时间呈周期性变化规律;时均速度并非随着与压电风扇自由端距离的增大呈现单调衰减的趋势,而是在距离压电风扇自由端距离为一倍振幅的截面上出现峰值速度最大的速度分布型,该位置正是涡环达到最大型面的瞬间涡核所处位置。涡串发展、运动过程中与周围流体发生干涉融合形成的射流起到了强化换热的效果,换热效果最好的地方不是出现在平衡位置,而是涡对破碎、流体紊流度最强的地方。     

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.     

Emitter Location Independent of Systematic Errors in Direction Finders

A scheme is suggested for the passive location of radio emitter position by using a mobile direction finder. The vehicle carrying the direction finder is made to maneuver such that the apparent direction of arrival is held constant. The resulting trajectory of the vehicle is a logarithmic spiral. The true direction of arrival can be obtained by monitoring the parameters of the spiral trajectory without using the value of the direction fimder reading. Two specific algorithms to eliminate direction finder bias are presented and their sensitivity to random errors in measurement assessed.     

基于正交试验的民用飞机抗爆结构参数敏感性分析

最小风险炸弹位置（LRBL）结构是放置飞机上可疑爆炸物的装置,探究结构尺寸和炸药位置对其抗爆性能的影响程度可为改进设计提供参考。基于正交试验设计与数值模拟相结合的方法,以LRBL 结构各危险部位的最大应变和变形为评价指标,分别运用极差分析法和方差分析法对LRBL 结构的罐体壁厚、底盖厚度、连接凸台厚度、剪切销直径和炸药位置5 个影响因素开展参数敏感性分析。结果表明：在200 g 炸药当量的工况下,各因素对LRBL 结构的抗爆性能的影响显著程度从大到小为：炸药位置、罐体壁厚、底盖厚度、凸台厚度和剪切销直径;结合评价指标综合分析得到各个因素最优水平下的LRBL 结构设计方案。     

Broadband passive acoustic technique for target motion parameterestimation

A nonlinear least-squares method is formulated to estimate the motion parameters of a target whose broadband acoustic energy emissions are received by a ground-based array of sensors. This passive technique is applied to real acoustic sensor data recorded during the passage of a variety of ground vehicles past a planar cross array and its effectiveness verified by comparing the results with the actual values of the target motion parameters. The technique cam also be applied to airborne targets     

基于压缩感知的金属加筋板兰姆波健康监测技术

针对大型复杂板结构安全评价需要，发展了一种基于压缩感知的金属加筋板结构兰姆波健康监测技术。利用压缩感知技术从稀疏阵列得到的少量检测数据中恢复出加筋板结构中兰姆波的频散特性，并提出了一种将余弦相似度和皮尔森相似度相结合的稀疏阵列兰姆波复合成像方法，以实现加筋板结构中大范围缺陷检测和成像。实验结果表明，压缩感知技术可以恢复出金属加筋板中兰姆波的频率-波数关系，提出的兰姆波复合成像方法能够实现金属加筋板中单缺陷和多缺陷的检测及定位。研究工作为复杂板结构损伤检测提供了一种可行的技术方案。     

单脉冲成像算法性能分析

单脉冲技术通过比较单个脉冲多路回波信号的信息实现对目标角度位置的精确测量,广泛运用于跟踪雷达中。在雷达成像中引入单脉冲技术可以显著提高前视这一合成孔径雷达(SAR)与多普勒波束锐化(DBS)成像盲区雷达图像的清晰度。本文着重对单脉冲成像算法的成像效果分析方法进行研究。从单脉冲和差比的概率密度函数出发,提出了目标图像位置失真、分辨率以及图像信噪比3个对图像质量进行衡量的指标。分析了决定这3个指标的系统及外部环境参数,并给出了相应的计算方法。最终通过数值积分以及Monte-Carlo仿真实验对理论分析结果进行了验证。     

Direction of arrival tracking below the ambiguity threshold

We present an algorithm for direction-of-arrival (DOA) tracking that allows operation below the ambiguity threshold of the direction-finding (DF) system. Using multiple target tracking techniques, the algorithm turns the most likely DOAs of each measurement into multiple potential tracks and then selects the true track as that with the maximum cumulative likelihood. The improvement offered by the algorithm, namely the extension of the ambiguity-free signal-to-noise ratio (SNR) domain, is demonstrated in several simulated experiments using several array structures, including a sparse array and a uniform linear array     

水下声呐探测系统信息支持下的直接攻潜作战仿真

在水下声呐系统目标指示条件下,进行直接鱼雷攻潜是1种创新型战法.针对直接空投鱼雷攻潜作战问题,将水声环境信息引入鱼雷目标识别过程,建立了更为逼真的模拟法效能评估模型.仿真分析了目标定位精度,投雷参数、鱼雷搜索参数等各关键因素对攻潜作战效果的影响,提出了在水下声呐基阵目标指示直接攻潜作战时,应重点关注的若干问题.     

壁面温度对斜爆震发动机进气道流动特性影响的数值研究

为研究壁面温度条件对层流、转捩、湍流状态下斜爆震发动机进气道流场结构、流场参数的影响,选取Ma10级、具有曲面压缩段的斜爆震发动机进气道为研究对象进行数值模拟,对进气道壁面附近激波诱导分离区、热边界层的变化进行了深入探讨。数值模拟结果表明,进气道肩部圆弧过渡段出现的再层流化现象,壁面冷却对其起抑制作用,绝热壁面条件下再层流化程度最为严重。壁面温度的增加有利于延缓流动转捩,同时也导致了分离区尺寸的增加以及转捩、湍流状态下分离区主体位置逐渐前移,进气道内通道的转捩为分离诱导转捩,转捩位置主要受到分离点位置的影响,整体表现为壁面温度增加转捩位置前移。进气道出口顶板侧热边界层厚度随着壁面温度的增加逐渐变厚,转捩状态下热边界层厚度变化可达5%,温度峰值也随着壁面温度的增加逐渐增加,且峰值位置逐渐靠近壁面。壁面温度条件相同时,层流状态下热流、热边界层厚度均较小。转捩、湍流状态下进气道出口顶板侧热边界层较厚,约为层流状态3倍,同时转捩、湍流状态下热边界层厚度相差可达2%。     

基于序列图像的航天器自主导航降维滤波方法

非合作目标的运动感知与状态估计,是太空领域技术发展的重要组成部分。非合作目标相对状态的精确估计是相对导航的难点问题。传统的非合作目标扩展卡尔曼滤波算法需要结合非合作目标的质心位置,增加了状态变量的维数,提高了系统不确定性,从而会影响状态扩展卡尔曼滤波的收敛速度。提出了一种基于序列图像的非合作目标相对导航方法,该方法在不对质心进行估计的情况下首先对非合作目标姿态进行估计,在完成非合作目标姿态估计后再对其质心进行估计。本文推导了光学相机测量值与目标真实姿态的关系,构建了基于序列图像的测量模型,分别建立了不含有非合作目标质心位置的状态方程和基于非合作目标位置、速度矢量的状态方程,设计了适用于非合作目标状态估计的扩展卡尔曼滤波算法。仿真实验表明该方法可在10 Hz采样频率下经过50次采样（即5 s）内快速收敛,从而有利于空间飞行器的在轨服务与维护。