三维运动声阵列对双点声源角跟踪指向性能研究

为了研究三维运动声阵列对真实目标在双点声源干扰下的二维角跟踪指向问题,分析了多点声源干扰的基本原理,建立了运动声阵列在双点声源下的角度跟踪指向性能数学模型;根据干扰目标与跟踪目标的声信号特性差异,分析了运动声阵列抗点声源干扰时的角度跟踪性能,得到了运动声阵列角度跟踪指向与干扰因素之间的关系;基于等功率双点声源辐射的假设下,建立了运动声阵列抗点声源干扰的角度跟踪指向评价指标,为进一步研究运动声阵列对多源声目标跟踪理论奠定了基础。

SESAT卫星姿轨控子系统和天线指向性能

本文介绍SESAT卫星姿态确定和控制子系统(ADCS)与推进子系统及有关设备、ADCS各种控制模式(包括天线方向图测试模式)及关键性能指标,概要介绍ADCS的动态试验。SESAT卫星在飞行任务的各个阶段都是三轴稳定的,ADCS采用标准敏感器配置(包括地球敏感器、太阳敏感器以及高精度陀螺),正常模式时的执行机构为陀螺稳定器(双框架动量轮——双框架具有两个自由度,动量轮转速可变),等离子体推力器用于轨道位置保持控制,肼推力器用于姿态控制。卫星上的有效载荷包括两架展开式固定天线和一架跟踪天线。

非接触界面耦合对超静卫星指向性能的影响

为了研究非接触界面耦合对超静卫星系统指向性能的影响,以弹簧阻尼单元代表非接触界面的耦合作用,并利用牛顿欧拉法建立了非接触作动超静卫星系统的刚柔耦合动力学方程。仿真结果表明:对于有效载荷模块,耦合使指向精度降低1个数量级,指向稳定度降低2倍;对于卫星本体模块,耦合使指向精度降低了2.5倍,对指向稳定度影响不显著。

基于SH0导波的电磁超声换能器设计与实验研究

传统基于周期性永磁体的电磁超声换能器结构较复杂,为此该文提出了一种由单一永磁体和导线阵列线圈构成的电磁超声换能器(EMAT)用于激发板中的SH0导波。首先叙述了设计的原理,并采用有限元软件进行三维数值仿真分析,利用水平极化永磁体垂直于板面的磁场在铝板中成功激发出SH0导波。为使EMAT换能效率达到最优,研究长和宽为10 mm×25 mm的永磁体,其高度及线圈匝数不同时EMAT激励的效率。仿真结果表明,选用永磁体高度为25 mm及线圈匝数为37时EMAT换能效率和声场指向性较好。在此基础上,通过实验研究了不同线圈匝数对换能器换能效率的影响,实验结果与仿真结果一致,充分验证了该文设计EMAT的方法具有可行性。

动中通天线在传统通信卫星系统中的应用

针对动中通天线的天线旁瓣、跟踪制导、交叉极化、失锁重捕等问题,就天线测试、邻星协调和系统设计等作了相关探讨。

非接触作动超静卫星动力学建模与仿真

为了研究非接触作动超静卫星的指向性能,利用牛顿-欧拉法建立了非接触作动超静卫星的多刚体动力学方程。针对惯性定向任务,设计了比例微分控制器。仿真结果表明,相比于传统卫星,所研究的超静卫星的指向精度和指向稳定度分别高出4个和5个数量级,验证了非接触作动超静卫星的高精度指向性能。

Performance analysis of relay-aided free-space optical communication system over gamma-gamma fading channels with pointing errors

The average bit error rate(ABER) performance of a decode-and-forward(DF) based relay-assisted free-space optical(FSO) communication system over gamma-gamma distribution channels considering the pointing errors is studied. With the help of Meijer's G-function, the probability density function(PDF) and cumulative distribution function(CDF) of the aggregated channel model are derived on the basis of the best path selection scheme. The analytical ABER expression is achieved and the system performance is then investigated with the influence of pointing errors, turbulence strengths and structure parameters. Monte Carlo(MC) simulation is also provided to confirm the analytical ABER expression.

Performance analyses of subcarrier BPSK modulation over M turbulence channels with pointing errors

An aggregated channel model is achieved by fitting the Weibull distribution, which includes the effects of atmospheric attenuation, M distributed atmospheric turbulence and nonzero boresight pointing errors. With this approximate channel model, the bit error rate （BER） and the ergodic capacity of free-space optical （FSO） communication systems utilizing sub- cartier binary phase-shift keying （BPSK） modulation are analyzed, respectively. A closed-form expression of BER is de- rived by using the generalized Gauss-Lagueree quadrature rule, and the bounds of ergodic capacity are discussed. Monte Carlo simulation is provided to confirm the validity of the BER expressions and the bounds of ergodic capacity.

Outage performance of multihop free-space optical communication system over exponentiated Weibull fading channels with nonzero boresight pointing errors

The outage performance of the multihop free-space optical(FSO) communication system with decode-and-forward(DF) protocol is studied by considering the joint effects of nonzero boresight pointing errors and atmospheric turbulence modeled by exponentiated Weibull(EW) distribution. The closed-form analytical expression of outage probability is derived, and the results are validated through Monte Carlo simulation. Furthermore, the detailed analysis is provided to evaluate the impacts of turbulence strength, receiver aperture size, boresight displacement, beamwidth and number of relays on the outage performance for the studied system.