基于月光偏振罗盘的载体自主定位方法

为了克服现有偏振定位技术无法全天时工作的缺陷,充分发挥偏振定位技术的自主性,提出一种夜间环境下基于月光偏振罗盘的载体自主定位方法。设计了仿生月光偏振罗盘传感器,改进了一种基于偏振度阈值检测的月亮高度角计算方法,通过实时更新月亮赤经、赤纬和格林时角,利用不同时刻的月亮高度角解算出载体经纬度信息。最后进行静态实验,验证了算法的可行性。实验结果表明,该方法可以稳定获取载体经纬度信息,且定位误差为42.34km。该方法增强了偏振定位技术的全天时性能,在夜间环境下的自主定位领域有着重要应用价值。     

星载柔性圆极化薄膜天线

近年来商业卫星产业发展迅速,从卫星物联网星座到高精度SAR成像,商业卫星的应用领域也越发丰富。区别于传统的大卫星,商业卫星主要集中在微纳、皮纳等卫星领域,最常见的为1U、3U、6U和12U等立方星。卫星平台的尺寸与载荷通信能力密切相关,微纳、皮纳等卫星平台由于尺寸较小,导致载荷通信能力严重不足。如何提升小卫星平台的通信能力,成为了商业卫星亟待解决的关键技术问题。薄膜天线具备可收纳展开特性,能够广泛应用于各种小卫星平台,在发射入轨前通过合理的收纳方式,收拢在小卫星平台尺寸内;在轨后,通过展开装置释放,形成较大辐射口径,有效提升卫星通信能力。由于薄膜厚度小（约0.1 mm左右）,Q值很高,限制了天线的带宽特性,也不便于实现圆极化辐射特性。以柔性薄膜（厚度约0.1 mm）为基础,以常规微带贴片为单元,通过旋转布阵以及多次顺序旋转馈电使该薄膜天线具备较好的圆极化、宽带特性,天线阵面规模为16×8,天线驻波（VSWR≤2.0）和轴比（AR≤3.0 dB）带宽可分别达到约10%和4%,法向最大增益可达24 dB,显著提升了薄膜天线的工作带宽和辐射特性。     

Influence of aircraft surface distribution on electromagnetic scattering characteristics

In this paper, two typical stealth aircraft concepts (wing fuselage blended and flying-wing) were designed. Then three gradually changed surface distribution models with the same plan-form for each concept were created. Based on the multilevel fast multipole algorithm (MLFMA), the vertical polarization transmitting/vertical polarization receiving (VV) and horizontal polariza-tion transmitting/horizontal polarization receiving (HH) radar cross section (RCS) characteristics were simulated with five frequencies between 0.1 and 1.0 GHz. The influences and mechanisms of aircraft surface distribution on electromagnetic scattering characteristics were investigated. The results show that for the wing fuselage blended concept, the VV RCS of this frequency range is higher than the HH RCS in most cases, while it is just the opposite for the flying-wing concept. As for the two aircraft concepts, the RCS levels of HH and VV both decrease with the frequency increasing, but the HH RCS has a faster downward trend. The surface distribution has little influ-ence on HH RCS characteristics. On the contrary, it has a significant impact on VV RCS charac-teristics, and the amplitude of the VV RCS increases with the surface thickness.     

Evolution of coronal mass ejections in the early stage

This work reports the investigation of two coronal mass ejections (CME) observed in white light, H, EUV and X-ray by various instruments both in space and on ground on February 18, 2003 and January 19, 2005, respectively. The white light coronal images show that the first CME began with the rarefaction of a region above the solar limb and was followed by the formation of its leading edge at the boundary of the rarefying region at altitude of 0.46 R from the solar surface. The rarefaction coincided the slow rising phase of the filament eruption, and the CME leading edge was observed to form as the filament eruption started to accelerate apparently. In the early stage of the second CME, a bright loop was first observed above the solar limb with height of 0.37 R in EUV images. We found that the more gradual CMEs initial process, the larger the timing difference between CMEs and their associated flares. The lower part of the filament brightened in H images as the filament rose to a certain height. These brightenings imply that the filament may be heated by magnetic reconnection below the filament in the early stage of the eruption. We suggest that the possible mechanism which led to the formation of the CME leading edge and cavity is magnetic reconnection which occurred under the filament when it reached a certain height.     

Force-free magnetic field in a cylindrical flux rope without a constant alpha

It is generally assumed that magnetic fields inside interplanetary magnetic clouds and flux ropes in the solar photosphere are force-free. In order to model such fields, the solution of rot B = B is commonly used where  = const. But comparisons of this solutions with observations show significant difference. To treat this problem,we examine the solutions with .     

靶场偏振成像技术应用

偏振成像技术不仅能获取目标的辐射强度信息,还能获取到偏振信息,有助于复杂环境下目标的探测识别.靶场现有光电设备主要采用强度探测,通过目标-环境差别来区分目标,因此,在复杂环境下,目标容易湮没在背景中难以探测.通过分析偏振成像原理和技术特点,总结归纳国外在偏振成像方面的试验应用,阐述了偏振成像在靶场应用的前景和优势,提出了一种基于偏振成像的光学成像系统,并对现有设备提出了偏振化改造方案.通过利用目标、环境的偏振特性,利用强度+偏振的组合模式,可提升现有设备的目标探测和成像识别能力.最后,对偏振技术应用和发展进行了展望.     

Collisional line broadening versus collisional depolarization: Similarities and differences

Within the impact approximation, collisional line broadening parameters and depolarizing and polarization transfer (population, orientation, alignment transfer) rates are complementary: both include the effect of collisional transitions between the Zeeman sublevels of a given level, or between fine or hyperfine structure levels of a given term. However, there are several differences: in line broadening, the two levels connected by the radiative transition contribute to the broadening, and there is also an interference term between these two levels, whereas only one level or two close levels are concerned in the depolarization. Another difference lies in the fact that purely elastic collisions contribute also to the line broadening, whereas they do not contribute to the depolarization. The nature of these two kinds of coefficients are recalled. Then the possibility to find some relationships or systematic trends concerning depolarization versus collisional broadening is considered. This is to answer some current questions which come from the polarization community.     

窄线宽单频单偏振环行腔掺铒光纤激光器

为了获得稳定的窄线宽单频单偏振掺铒光纤激光器输出,对采用饱和吸收体的环行腔结构掺铒光纤激光器进行了研究.实验中采用未抽运掺铒光纤作为饱和吸收体形成窄带滤波器,并选用高反射率的光纤光栅作为波长选择元件,同时采用具有高消光比的保偏环行器来获得单偏振激光.窄线宽单频单偏振环行腔掺铒光纤激光器的峰值波长可以通过拉伸光纤光栅进行调谐,调谐的范围为1548~1552nm.当抽运功率为275mW时获得的输出最大功率55.4mW.通过采用光纤延迟自外差法的线宽测试技术测量出该环行腔掺铒光纤激光器的20dB线宽为3kHz,光纤激光器的输出光偏振态长时间稳定在偏振度99.9%.这种窄线宽单频单偏振掺铒光纤激光器可以作为相干激光雷达的稳定信号源.      

自适应三维极化滤波

三维极化滤波能够更好地利用空域信息,在极化域-空域联合滤波,因此能够抑制二维正交极化滤波不能滤除的干扰,达到更好的滤波效果.实际应用中,信号通常是未知的或者变化的,要达到好的滤波效果,必须实时更新滤波参数.针对未知的或缓变的信号环境,提出了一种自适应三维极化滤波算法,利用历史杂波数据来估计杂波的极化信息,据此对天线进行调整,以对接收信号滤波.最后通过Matlab仿真验证了该算法的有效性.     

改变微带天线基板形状实现圆极化

实现微带贴片天线圆极化的方法中,传统方法主要是设计适当的金属贴片形状和选择适当的馈电方式,而一种新思路即设计适当的介质基板形状,在某些使用环境中可以提供较大的方便。通过计算发现新思路有其可行性和工程价值,在某些方面有其独特的优势。