星载高增益毫米波SAR相控天线阵设计

介绍了一种高增益、高效率的星载毫米波合成孔径雷达(SAR)有源相控天线阵的设计。天线单元采用了窄边开缝的波导缝隙天线，辐射缝隙与波导宽边垂直，天线具有效率高、匹配良好的特点。在方位向，波导缝隙天线组成直线阵，直线阵内采用折叠的波导功分器降低了直线阵的剖面高度。在距离向，波导缝隙直线阵紧密排布，形成一维相扫阵列。定标网络及馈电网络均采用波导形式并集成于天线阵列背面，其中，定标网络通过定向耦合器改善了定标通道的一致性及带内起伏特性，馈电网络通过魔T结构改善各有源通道间的隔离度。以距离向84个直线阵为一个子阵列，最终设计的天线全阵在方位向共包含8个子阵列，总体尺寸是595.8λ0×56λ0(λ0是中心频率在自由空间中的波长)。实测天线带内最高增益为54.37 dBi，辐射效率65.2%。天线阵列具有高增益、高效率的优点，同时结构简洁紧凑，适用于星载毫米波SAR系统。     

一种星载伞天线展开机构研究

天线展开机构使用动力绳实现天线展开和收拢过程中易出现动力绳松弛、脱槽现象。以星载高精度伞状天线展开机构为研究对象，分析天线展开机构的工作原理；利用解析法获得展开机构的运动方程，结合天线展开机构运动部件结构参数，得到天线展开过程中展开机构动力绳的松弛规律；建立以展开机构结构参数为设计变量，以动力绳松弛量最小为目标的展开机构结构优化模型，通过模拟退火法进行求解，得到优化的展开机构结构参数，通过优化前后的展开机构展开、收扰功能试验，测试了机构工作时动力绳的松弛量，验证了展开机构优化的正确性。结果表明：优化后的展开机构动力绳松弛量较优化前降低了90%，优化效果显著。     

基于液体金属的接触PIM抑制方法和实验验证

接触非线性是射频设备和电路中产生无源互调（passive intermodulation，PIM）信号的重要原因之一。基于对接触结点射频等效电路的分析，提出了一种基于共晶镓铟合金（eutectic gallium-indium，EGaIn）的PIM抑制方法。EGaIn不同于传统的焊锡，它可以在室温下实现接触结位置上的稳定、可重构连接。首先分析了射频（radio frequency，RF）下的金属接触结的电路模型。其次设计并实现了两个包含不同金属接触结构且工作在2.6GHz的平面倒F天线（planar inverted F antenna，PIFA）。最后比较了EGaIn焊接前后PIFA的互调水平，其中对PIM指标的最大抑制程度为35dB。验证了EGaIn可以在室温下对PIFA的接触结点进行可重构焊接，这为电连接中的非线性抑制提供了一种参考方法。     

Structural design and model fabrication of cable-rib tensioned deployable parabolic cylindrical antenna

Deployable mechanisms with light weight and high storage ratio have received considerable attention for space applications. To meet the requirements of space missions, a parabolic cylindrical deployable antenna based on cable-rib tension structures is proposed and verified by a physical prototype. The parabolic cylindrical antenna adopts simple parallel four-bar mechanisms to construct the basic deployable unit, and the cylindrical direction dimension can be easily extended by modularization, which has obvious advantages in storage ratio and area density. Considering the complexity of the entire antenna structure design, including cable networks and flexible trusses, the form-finding design optimization model of a parabolic cylindrical antenna is established using the force density sensitivity method, and then the kinematics analysis of the deployable mechanism is carried out. Finally, a single-module prototype with a deployable diameter of 4 m × 2 m was designed and fabricated. The results of the ground deployment process test and surface accuracy measurements show that the antenna has good feasibility and practicability.     

索网结构非线性有限元分析中初始张力状态的快速构造方法

预应力索网结构是以柔性拉索为主要承重构件或辅助承重构件的一种结构体系,用于可展开天线等空间结构。为在有限元数值分析时准确、高效地施加张拉预应力,综合考虑索网的几何非线性、刚度矩阵奇异性、索网与支撑结构存在耦合变形等问题,利用索网式可展开天线的特性,在非线性有限元计算时忽略初位移刚度矩阵,将问题线性化,并详细介绍了以降温法模拟预应力时降温值的计算过程。此方法无需迭代,且得到的降温值在用于索网非线性计算时具有足够的精度;此方法能充分利用通用有限元计算程序,可进一步开展模态和响应等力学计算,便于在工程中实际应用。     

美国地下领域无人系统发展现状及启示

随着科学技术的高速发展,地下领域(如天然洞穴网络、人造隧道和城市地下环境等)逐渐成为人类研究的热点,利用无人系统在地下等复杂场景执行探索、搜索与搜救等任务仍面临着许多挑战.深入分析了美国地下领域无人系统技术发展的模式框架,梳理了快速轻量自主、机械天线和地下挑战赛等DARPA典型研发项目的 研究目标与现状,提炼出地下领域无人系统需要解决的关键技术,在此基础上归纳总结了美国地下领域无人系统的发展趋势.最后,结合国内发展情况提出了地下领域无人系统的发展启示.     

卫星导航有源接收天线噪声温度测量

卫星导航有源接收天线的噪声温度是导航接收系统的关键技术指标之一。针对卫星导航有源天线总体噪声温度无法测量的问题，研制了两台口面型噪声源，口面噪声源主要由辐射体、辐射体物理温度控制和温度测量仪等组成。两个口面噪声源在L和S波段分别提供高低温标准噪声温度，采用Y系数测量方法测量有源接收天线的总体天线噪声温度。测量了某卫星导航有源天线的总噪声温度，在(1.19～1.29) GHz的频率范围内，中心频率1.24 GHz上噪声温度测量结果为206 K，但是在1.266 GHz频率点上噪声温度测量大于4 000 K，说明天线与滤波器之间、滤波器与放大器之间存在设计问题或其它问题，体现出测量有源天线噪声温度的必要性。     

Optimal crater landmark selection based on optical navigation performance factors for planetary landing

Planetary craters are natural navigation landmarks that widely exist and are easily observed. Optical navigation based on crater landmarks has become an important autonomous navigation method for planetary landing. Due to the increase in observed crater landmarks and the limitation of onboard computation, the selection of good crater landmarks has gradually become a research hotspot in the field of landmark-based optical navigation. This paper designs a fast crater landmark selection method, which not only considers the configuration observability of crater subsets but also focuses on the influence on navigation performance arising from the measurement uncertainty and the matching confidence of craters, which is different from other landmark selection methods. The factor of measurement uncertainty, which is anisotropic, correlated and nonidentically distributed, is quantified and integrated into selection based on crater pairing detection and localization error evaluation. In addition, the concept of the crater matching confidence factor is introduced, which reflects the possibility of 2D projection measurements corresponding to 3D positions. Combined with the configuration observability factor, the crater landmark selection indicator is formed. Finally, the effectiveness of the proposed method is verified by Monte Carlo simulations.     

Compact wideband FSS-absorber-based low-RCS reflectarray antenna

This paper presents a method to realize compact broadband low-RCS Reflect Array(RA) antenna based on a Frequency Selective Surface(FSS) absorber and a reflective metasurface.Such an FSS absorber consists of a resistance-loaded lossy layer and an FSS layer, which is utilized to reach an absorption-transmission response. The bottom reflective metasurface works as a phase array, reshaping the quasi-sphere wave from the feeding antenna into the quasi-plane wave. As a demonstration, the low-RCS RA an...     

Influence and experiment of cable-net manufacturing errors on surface accuracy of mesh reflector antennas

Cable-net structures are of substantial importance in the construction of large mesh reflector antennas. Owing to the inevitable errors in their manufacturing process, the reflector surface accuracy deteriorates. This study makes a comprehensive investigation of random manufacturing errors during constructing the mesh reflector antennas, and analyze its influence on reflector surface accuracy. Firstly, the sensitivity of reflector surface accuracy with respect to the random errors of the unstressed cable length is mathematically deducted. Secondly, a non-button connecting method is proposed and analyzed to reduce manufacturing errors. Thirdly, two physical experiment models based on 2.62-meter mesh reflector antenna are made. Finally, numerical examples and experimental tests are given to demonstrate the effectiveness of the proposed method. Compared with the traditional method, the proposed method can effectively reduce the influence of the manufacturing errors on the reflector surface accuracy. Moreover, the reduction in the sizes of the nodes also reduces the risk of entanglement of the mesh reflector antenna during the deployment process, and thereby improves the deployment reliability.