离焦对激光通信接收视场的影响分析

为了降低自由空间激光通信中对准难度,本文提出了采用离焦的方法以增大接收视场角。以满足通信所需最低能量(-35 d Bm)为基准,理论推导了探测器接收能量、接收视场角(FOV)、离焦接收能量及离焦量之间的相互关系,并通过Matlab仿真,分析对比了离焦接收能量和离焦量对接收视场角的影响。结果显示,当离焦量为0.5 mm时,离焦接收能量从-20.9 d Bm提高到-4.1 d Bm,接收视场角能增大0.27 mrad;当离焦接收能量为-4.1 d Bm时,离焦量从0.2 mm扩大到1.0 mm,视场角能增大1.75 mrad。通过对比表明,提高离焦接收能量以及扩大离焦量都可以增加接收视场角,且扩大离焦量的效果相对比较明显,这对后续离焦系统的设计提供了理论指导依据。     

A hybrid adaptively genetic algorithm for task scheduling problem in the phased array radar

A phased array radar (PAR) is used to detect new targets and update the information of those detected targets. Generally, a large number of tasks need to be performed by a single PAR in a finite time horizon. In order to utilize the limited time and the energy resources, it is necessary to provide an efficient task scheduling algorithm. However, the existing radar task scheduling algorithms can't be utilized to release the full potential of the PAR, because of those disadvantages such as full PAR task structure ignored, only good performance in one aspect considered and just heuristic or the meta-heuristic method utilized. Aiming at above issues, an optimization model for the PAR task scheduling and a hybrid adaptively genetic (HAGA) algorithm are proposed. The model considers the full PAR task structure and integrates multiple principles of task scheduling, so that multi-aspect performance can be guaranteed. The HAGA incorporates the improved GA to explore better solutions while using the heuristic task interleaving algorithm to utilize wait intervals to interleave subtasks and calculate fitness values of individuals in efficient manners. Furthermore, the efficiency and the effectiveness of the HAGA are both improved by adopting chaotic sequences for the population initialization, the elite reservation and the mixed ranking selection, as well as designing the adaptive crossover and the adaptive mutation operators. The simulation results demonstrate that the HAGA possesses merits of global exploration, faster convergence, and robustness compared with three state-of-art algorithms—adaptive GA, hybrid GA and highest priority and earliest deadline first heuristic (HPEDF) algorithm.     

空间激光通信中光强起伏尺度特征的数值分析

利用数值模拟的方法，定量地计算分析了空间激光通信中光强起伏问题，得到了准直光束与聚焦光束光强起伏相关距离（不均匀元半径）随大气相十长度变化的结果；进而分别从接收效率和性价比等不同的角度对激光通信系统接收孔径选取的参考因素进行了探讨。根据现代光通信对误码率的最低要求定义最佳接收孔径，计算分析了聚焦光束空间激光通信系统最佳接收孔径随大气相干长度r0的变化关系。结果表明，最佳接收孔径随大气相干长度的减小而迅速增大。对于聚集光束空间激光通信而言，在大气相干长度ro约为4cm的强湍流效应情况下，通信系统的接收孔径接近5倍艾里斑直径，才能满足国际电信联盟-电信标准部对光通信的最低要求。     

微波耦合场测量圆环探头的接收特性

 为了准确测量腔体等封闭狭小空间内微弱耦合电磁场，对一般小型圆环同轴探头的连接端面进行斜面剖分优化处理。采用时域有限差分方法，模拟了在电磁脉冲平面波激励下，圆环斜面探头所感应电压的时域变化过程。通过数值模拟计算，对比分析了３种不同角度斜面圆环探头的电磁接收频率响应特性，得出带有15°斜面圆环探头的高频接收性能相应提高2~5 dB。开展直径40 mm圆环15°斜面探头的电磁接收测量实验，并与相应计算结果进行对比分析，其二者整体变化趋势基本吻合，从而验证了数值计算分析探头电磁接收特性结果的准确性。     

圆柱类构件超声相控阵聚焦模型

在利用平面相控阵超声换能器对圆柱类构件检测时，受曲界面结构引起的入射波和回波时延的影响，扫描声束的波阵面产生弯曲，在利用传统迭代遍历算法计算延迟时间时效率低，无法发挥相控阵换能器检测优势。针对上述问题，建立了一种基于圆柱类构件特征和耦合介质特性的超声相控阵扫描成像的聚焦模型。该模型基于换能器、耦合介质、圆柱类构件材料特性和几何关系以及声线模型和折射定律，建立了耦合介质及被检构件的声速、曲面曲率半径、阵列与曲面间的距离等关联的延迟时间聚焦控制模型。利用该模型计算出的延时时间，对各阵元发射时间进行控制，从而实现扫描声束的聚焦。该文以液体和有机玻璃制介质楔块为例，对圆柱钢曲面的相控阵声束聚焦进行了仿真实验，结果表明该文方法计算效率显著提升，同时声束可以在预设位置实现聚焦，验证了该模型在计算效率上的优势与有效性。     

20 Hz~10 kHz光纤水听器相移灵敏度校准

利用相位生成载波解调技术精确测量光纤水听器的光相移量,在20 Hz~10 kHz频率范围实现了光纤水听器探头相移灵敏度的校准.20 Hz~1.25 kHz频段采用驻波管比较法进行校准,1.25 kHz~10 kHz频段采用自由场脉冲比较法进行校准.利用本文建立的校准系统,对TMD 35#光纤水听器的相移灵敏度进行校准,校准结果表明,两种方法测得的相移灵敏度具有很好的一致性,在1.25 kHz频率点的相移灵敏度值偏差为0.8 dB.不确定度分析表明,该校准系统的扩展不确定度(k=2)为0.9 dB.     

Simulation analysis of an active cancellation stealth system

Active cancellation stealth is a smart signal blanking method, that it has become an important developing direction on modern stealth technology. In order to further explore the active cancellation stealth technology, we are considering the detection and cancellation of receiving/transmitting antenna pattern is different. Put forward active cancellation system simulation structure diagram based on MATLAB/SIMULINK, where the phased array radar system as the modelling object, and established the active cancellation stealth system mathematical model based on digital radio frequency memory (DRFM) and the radar signal processing system of the coherent video simulation model, based on linear frequency modulation and radar coherent pulse signal simulation, verified the rationality and validity of the design, as the active cancellation stealth engineering technology laid the foundation.     

Thermally tuned optical fiber for true time delay generation

A new technique for generating a continuous range of true time delay values is introduced. Heating optical fiber in order to change the effective index of the guided mode produces time delays. A 45-m section of single-mode silica fiber is demonstrated to produce a continuous range of time delay values from 0 to 211 ps over a temperature tuning range of 50°C (30–80°C). A thermal time delay factor is introduced and found to be 0.096 ps/m°C for Corning LEAF fiber. A 7.66-m section of multimode Lucina polymer fiber is demonstrated to produce a range of time delay values from 0 to 32 ps over a temperature tuning range of 30°C (30–60°C). The thermal time delay factor for this fiber is −0.1427 ps/m°C.     

矩形点阵法测量激光测距机瞄准轴与接收轴一致性

针对激光测距机瞄准轴与接收轴一致性的测量，提出了一种新的方法——矩形点阵法，并通过大量的实验验证了此方法的可行性。通过对结果的计算和误差分析，确定了此方法能够使激光测距机的发射次数在50次以内，测量精度达到10″以内。为激光测距机瞄准轴与发射轴平行性的自动测量提供了一种途径。     

面向低强度无线网络信号接收谱参数估计研究

针对以北斗卫星导航信号为代表的亚纳秒级的低强度无线网络信号在定位中难以获取精确时间估计及角度估计,且易受环境噪声影响,使其定位精度不高等难题,本文提出了基于亚纳秒级的低强度无线网络信号接收谱参数估计方法。首先通过抽样方式,将发射信号抽样为多维独立子信号并独立建模,通过构造噪声空间与子信号空间在对应列向量正交化的基础上精确获取TOA估计;随后利用复数域映射,在获取TOA估计基础上采取比对方式精确地获取DOA估计。最后对本文参数估计方法进行了精度分析。测试数据显示：与 PM算法、ESPRIT算法相比,本文技术在TOA及DOA估计上更为精确;同时在信号强度低且背景噪声干扰严重的情况下,本文方法仍可有效的维持参数估计精度。