星载可展开天线研究

海洋二号卫星微波校正辐射计天线(HY-2 CRA)是高增益、低副瓣、高波束效率、低损耗的天线子系统. 其高主波束效率、低损耗等要求对天线展开精度、形面精度、测试等提出了极大挑战. 由于卫星发射整流罩结构限制, 天线采用可展开机构形式, 并用正交模耦合器实现频率复用. 天线频率分别达到18.7 GHz, 23.8 GHz 和37 GHz.为了减小天线形面变形, 保证天线波束指向, 天线反射面(包括反射面支架、馈源支架)采用碳纤维复合材料, 确保天线在宇宙空间变形尽可能小. 本文就HY-2 CRA的设计、加工、测试等进行了论述.     

一种等离子体诊断的开放式谐振器研究

本文提出了一种可用于等离子体诊断的开放式谐振器设计。谐振器由高Q型谐振腔和点聚焦天线组成,并通过强耦合孔将两者结合。高Q型谐振腔的部分能量由强耦合孔辐射至天线,经点聚焦天线将辐射能量汇聚于等离子体层。由等离子体电子密度变化引起天线反射系数的变化,该变化与高Q型谐振腔互作用后引起谐振频率和Q值的变化。经实际测试,随着等离子体电子密度的升高,谐振腔的谐振频率和Q值呈现上升趋势,可用于实现等离子体电子密度的非接触性探测。     

双星定向试验研究

在前期的模糊度求解方法探讨及精度仿真分析的基础上,集成了一套双天线的北斗定向系统,并进行了大量的静基座及车载试验,对实际定向结果进行了精度分析．试验结果证实,静基座旋转基线及作者所提出的车载等效转动基线解模糊方法是可行的,系统的静态重复精度(1σ)优于方位角0．016 27°、俯仰角0．012 97°, 静态方位绝对精度优于0．358 95°,动态方位稳定度达0．08602°．双星定向可在实际应用中以短时间提供较高精度方位信息．该项技术将进一步拓展当前北斗卫星系统功能．     

小型铯原子钟微波腔调谐过程的仿真研究

通过建立模型,利用Ansoft HFSS 12.0对小型铯原子钟内微波腔的调谐过程进行了仿真,得到了调谐棒半径、在调配器内长度与微波腔谐振频率之间的关系曲线。结果表明,调谐棒半径一定时,调谐棒长度在一定范围内,微波腔谐振频率随着长度的增加逐渐下降;随着半径的增大,微波腔谐振频率的变化范围逐渐增大,在铯原子跃迁中心频率处,调谐棒长度对微波腔谐振频率的影响变大。根据仿真结果,给出了调谐棒半径的取值范围,为微波腔的设计、加工和调谐提供了理论指导。     

不完整带隙结构在微带天线中的应用

为了使微带贴片天线满足导航和通信等应用设计的某些特殊要求,提出了一种可改善微带天线性能的不完整电磁带隙结构:首先在普通的切去两个对角的方形圆极化贴片天线周围一定距离处附加电磁带隙结构,使谐振频率增加而带宽变化不大;然后,在此基础上又将接地板外侧四边切去窄方形金属层,从而形成方形环介质层.仿真结果表明:新型结构可提高传统贴片天线的低仰角增益和总增益,同时可使传统微带天线较好地实现双频工作.      

非均匀间距的低副瓣宽带微带阵列天线设计

为降低天线副瓣电平（SLL）和展宽带宽,设计了一款谐振频率为14.25 GHz的16阵元非均匀间距的耦合馈电微带阵列天线。天线采用多层设计,通过在接地板开矩形槽进行耦合馈电,并引入空气层,降低天线Q值,增大带宽。区别于均匀间距阵列天线的激励幅值加权,从阵元间距角度入手,利用差分进化算法降低副瓣电平,构建非均匀间距并联线阵天线。用槽面辐射的能量近似代替阵元接收的能量,观察阵元功率分配情况,并建立馈电网络所有馈线段的数学关系,保证非均匀间距条件下所有阵元为等幅同相激励。测试结果显示,天线在14~14.5 GHz范围内电压驻波比小于2,满足了卫星动中通的带宽要求;工作带宽内增益大于16 dB,副瓣电平低于-16 dB,性能优于均匀间距阵列天线。      

一种用于测量谐振频率和Q值的数字系统

最近研制和测试了一种用于准确测量射频和微波谐振电路的谐振频率和Q值的计算机控制的自动系统。在此系统中,谐振曲线的拐点利用联机数字计算机通过数学计算过程进行识别,并利用它计算谐振频率和Q值。这个系统的主重优点是它的结果与谐振电路谐振频率的性能无关,与信号源的3dB点、幅度、频率漂移无关。也与检测器的不稳定性无关。设计、安装并测试了一种在1—2千兆赫之间工作的试验系统,用实验室小型计算机PDP11/34进行数据采集与处理以及对整个系统的控制。Q值的测量范围在100—1500之间,估计的谐振频率的不确定度为40ppm,Q值为1000的谐振电路的Q值的不确定度为百分之七。     

考虑在轨热效应的网状天线索网优化设计

网状天线服役于高低温、强辐射的复杂太空环境,其热变形是影响天线在轨性能的重要因素。目前的设计方法均为常温下的索段预应力配置,难以计及服役环境对天线在轨性能的影响。通过在索网模型中引入温度载荷,建立了以常温下索段参数为变量,以服役环境下的索网形面精度和张力分布为目标及约束条件的索网优化模型,从而在设计之初充分考虑服役热环境下的天线性能,改善天线在轨精度和张力分布。分析了天线运行轨道热环境,计算了天线在不同轨道位置的温度场;基于非线性有限元理论,建立了网状天线热结构模型,形成了考虑温度效应的索网找形及优化设计方法;开展了面向天线服役性能的索网优化设计。优化结果表明,该方法有效提高了天线在轨运行时的性能,可为考虑服役环境的网状天线优化设计提供方法和思路。     

复杂动力学模型下星载天线跟瞄控制技术研究

针对星载天线动力学复杂这一问题,从天线系统刚柔耦合动力学建模、指向跟踪控制以及振动抑制等方面研究了柔性星载运动部件的指向控制方法。首先,通过描述系统几何拓扑关系建立系统运动学方程,从而简化动力学建模过程;之后,利用假设模态法,对天线反射面挠性进行建模;最后,将拉格朗日方程与挠性关节模型相结合,从而建立了星载天线非线性刚柔耦合动力学模型。在以上复杂动力学建模的基础上,采用分层设计的思路进行了控制策略设计：先运用基于计算力矩法的滑模控制器得到不考虑挠性关节的耦合控制律,从而保证卫星基体的稳定性以及天线挠性反射面的振动抑制;再使用反步法对挠性关节进行控制,实现对天线反射面的指向精度控制。最后,讨论了动力学参数不确定性对系统跟踪指向控制的影响并采用数学仿真的方式验证了相关动力学模型与控制算法。仿真结果表明该方法能较好地实现对星载天线的指向跟踪控制以及振动抑制,提高星载天线的动态指向精度。     

宽带双极化天线测量探头的设计与仿真

天线测量探头的性能对提升天线平面近场测量效率、最终测量结果的精度具有重要意义。针对平面近场测量的需要,应用反向四脊和差分馈电技术,设计了宽带双极化天线测量探头。对测量探头模型进行仿真,分析了带宽、方向图、隔离度和交叉极化辨识度等探头性能,确定了高隔离度、高极化纯度的宽带双极化天线测量探头的最优设计,获得了更高精度和效率的天线测量。     

基于虚拟仪器的空靶通用测试系统的研究

针对空中靶标测试设备现状和问题,提出了一种基于虚拟仪器的新型空靶通用化测试系统,研究了其总体结构和功能特点, 讨论了系统软件体系结构和开发设计。     

Monitoring of long-term land subsidence from 2003 to 2017 in coastal area of Semarang,Indonesia by SBAS DInSAR analyses using Envisat-ASAR,ALOS-PALSAR,and Sentinel-1A SAR data

Land subsidence is a critical issue that large cities located in coastal areas, such as Semarang, Indonesia, must address. The monitoring of land subsidence is vital for predicting and mitigating the disasters that such subsidence may cause. Therefore, an economical and effective monitoring method, which can continuously provide accurate measurements over extensive areas, is highly required. Differential Interferometry Synthetic Aperture Radar (DInSAR) has the potential to be a powerful technique that can meet the above demands. Actually, DInSAR has been applied to monitor the subsidence in Semarang, but it was for a limited period before 2012.In order to clarify the transition of the long-term subsidence behavior in Semarang, the Small Baseline Subset (SBAS) method, which is one type of time-series DInSAR, is employed in this research. The sets of data of Envisat-ASAR (2003–2007), ALOS-PALSAR (2007–2011), and Sentinel-1A (2015–2017) are employed for the analyses. Then, the validity of the SBAS results is discussed from the viewpoints of both spatial distribution and temporal transition using GPS displacement measurement results and the geological conditions of the ground.On the other hand, as the lifespan of SAR satellites is commonly designed to be around 5–7?years, an appropriate method, which can connect the subsidence provided independently by the unlinked time-series data sets of the three different SAR satellite data, is required. This study uses the Hyperbolic Method (HM) to connect the above unlinked SBAS results. The HM is often used to fit the monitored subsidence in practice as a geotechnical engineering tool. Using this method, 14?years of the temporal behavior of the subsidence in Semarang is evaluated.It is found that the transition of the subsidence is different depending on the location, and that the subsidence rate is still increasing in the north and northeast parts of the coastal area. This study shows that SBAS DInSAR can be a useful tool for long-term continuous subsidence monitoring.     

Physical assessment of coastal vulnerability under enhanced land subsidence in Semarang,Indonesia, using multi-sensor satellite data

Research has been conducted in Semarang, Indonesia, to assess coastal vulnerability under enhanced land subsidence using multi-sensor satellite data, including the Advanced Land Observing Satellite (ALOS) Phased Array type L-band SAR (PALSAR), Landsat TM, IKONOS, and TOPEX/Poseidon. A coastal vulnerability index (CVI) was constructed to estimate the level of vulnerability of a coastline approximately 48.68?km in length using seven physical variables, namely, land subsidence, relative sea level change, coastal geomorphology, coastal slope, shoreline change, mean tidal range, and significant wave height. A comparison was also performed between a CVI calculated using seven parameters and a CVI using six parameters, the latter of which excludes the land subsidence parameter, to determine the effects of land subsidence during the coastal vulnerability assessment. This study showed that the accuracy of coastal vulnerability was increased 40% by adding the land subsidence factor (i.e., CVI 6 parameters?=?53%, CVI 7 parameters?=?93%). Moreover, Kappa coefficient indicated very good agreement (0.90) for CVI 7 parameters and fair agreement (0.3) for CVI 6 parameters. The results indicate that the area of very high vulnerability increased by 7% when land subsidence was added. Hence, using the CVI calculation including land subsidence parameters, the very high vulnerability area is determined to be 20% of the total coastline or 9.7?km of the total 48.7?km of coastline. This study proved that land subsidence has significant influence on coastal vulnerability in Semarang.     

Concept options for the aerial survey of Titan

Various aerial platforms intended for long endurance survey of the Titan surface are presented. A few novel concepts are introduced, including a heated methane balloon and a balloon with a tethered wind turbine. All the concept options are predicted to have lower scientific payload fractions than the Huygens probe. It is concluded that the selection of the best aerial platform option depends on more accurate mass estimates and a clear decision on whether, or not, in situ surface composition measurements are required in conjunction with aerial remote sensing.     

基于时空协同的飞行器集群制导技术现状与应用

从集群作战军事需求牵引角度,指出了基于时空协同的多飞行器制导技术,是有效提高突防概率与目标打击效能的关键支撑技术。围绕飞行器集群协同制导技术发展现状,分别以时间协同约束、空间协同约束及时空协同约束为主线,介绍了国内外技术的发展思路。最后,对飞行器集群协同制导技术进行了概括总结,并对该技术在未来的发展方向进行了展望。     

基于改进YOLO V5的无人机航拍图像小目标检测方法

本文针对无人机航拍目标检测技术中目标聚集、目标较小及实时性差等问题,将YOLO V5的主干架构进行改进,简化Neck网络,提出了一种提高检测速度又能准确识别的无人机航拍图像检测技术方案。经过仿真实验测试,改进后的YOLO V5网络在保持识别精度的同时,检测速率提升了31%,满足无人机在航拍作业时对于准确性与实时性的要求。     

Vertical motions in Thailand after the 2004 Sumatra–Andaman Earthquake from GPS observations and its geophysical modelling

Following previous findings from ongoing GPS research in Thailand since 2004 we continue to exploit the GPS technique to monitor and model land motions induced by the Sumatra–Andaman Earthquake. Our latest results show that up to the end of 2010, Thailand has been co-seismically displaced and is subsequently undergoing a post-seismic horizontal deformation with total displacements (co-seismic plus post-seismic) ranging from 10.5 to 74.7 cm. We observed the largest horizontal displacements in the southern part of Thailand and moderate and small displacements in the central and northern parts. In addition to horizontal displacements throughout Thailand, continuous GPS measurements show that large parts of Thailand are subsiding at rates up to 1 cm/yr. It is the first time that such vertical post-seismic deformations at large distances (650–1500 km away from the Earthquake’s epicentre) have been recorded. We have investigated the physical processes leading to the observed subsidence. While after-slip on the subduction interface induces negligible or even slightly positive vertical motions, relaxation in the asthenosphere is associated with a sizable subsidence. Predictions from a 3D finite element model feature an asthenosphere with an effective viscosity of the order of 3 * 10¹⁸ Pas, fit the horizontal post-seismic data and the observed subsidence well. This model is then used to predict the subsidence over the whole seismic cycle. The subsidence should go on with a diminishing rate through the next two decades and its final magnitude should not exceed 10 cm in the Bangkok area.     

Subsidence rate monitoring of Aghajari oil field based on Differential SAR Interferometry

Land subsidence, due to natural or anthropogenic processes, causes significant costs in both economic and structural aspects. That part of subsidence observed most is the result of human activities, which relates to underground exploitation. Since the gradual surface deformation is a consequence of hydrocarbon reservoirs extraction, the process of displacement monitoring is amongst the petroleum industry priorities. Nowadays, Differential SAR Interferometry, in which satellite images are utilized for elevation change detection and analysis – in a millimetre scale, has proved to be a more real-time and cost-effective technology in contrast to the traditional surveying method. In this study, surface displacements in Aghajari oil field, i.e. one of the most industrious Iranian hydrocarbon sites, are being examined using radar observations. As in a number of interferograms, the production wells inspection reveals that surface deformation signals develop likely due to extraction in a period of several months. In other words, different subsidence or uplift rates and deformation styles occur locally depending on the geological conditions and excavation rates in place.     

空中加油软管“甩鞭”现象安全性分析与仿真验证

对于软管式空中加油系统,由于受到加油机尾流、大气紊流、受油机艏波、飞行员操作水平、燃油压力脉动等各种因素干扰,加油软管难以稳定在平衡位置,在对接时常发生软管“甩鞭”现象（HWP）。软管“甩鞭”现象严重影响了空中加油任务的安全性,降低对接成功率,是空中加油过程的一种典型危险。基于系统理论事故模型和过程模型（STAMP）理论和系统理论过程分析（STPA）方法对空中加油过程的典型危险——HWP,开展了具体的致因分析,从控制模型的角度系统分析导致HWP发生的不安全行为和相应的致因场景,从系统层、不安全控制行为层和致因因素层分别提出避免空中加油软管HWP发生的一系列安全约束。根据软管HWP的危险功能控制结构,利用Simulink工具搭建仿真验证平台,以对接速度、卷盘机构控制、软管长度关键致因为模型输入,验证所提安全约束的准确性和可行性。      

一种无人机通用综合检测系统

为了增强无人机系统检测控制设备的通用性,提高检测精度,设计了一种基于面向仪器系统的PCI扩展(PXI)总线及虚拟仪器(VI)的无人机通用综合检测系统.针对无人机系统工作的特点,从功能设计、体系结构、软硬件设计等方面对该系统的通用性进行了探讨.该系统采用了虚拟仪器技术,硬件设计采用PXI体系结构,软件以LabWindows/CVI作为开发平台.通过配备不同的接口适配器和对软件参数设置进行相应更改,可适用于不同型号的无人机电气、舵机、发动机、起飞和回收等系统检测.同时提供矩阵输出,利用系统资源满足无人机各种信号测试/激励的需求.该系统已成功应用于某复杂型号无人机的地面综合检测.