Low multipath antennas for GNSS-based attitude determination systems applied to high-altitude platforms

High-altitude platforms (HAPs) are a flexible and attractive technology for providing innovative wireless services. These aerial platforms can be successfully employed for mobile or broadband communications and for disaster monitoring or response. However, one of the open issues is whether HAP stations can provide reliable services without temporal outages owing to stratospheric winds that can cause positional and attitude instabilities thus affecting the communication system operation. To counteract this issue, one possible solution is to use reconfigurable antennas whose pointing direction can be adjusted depending on the platform spatial orientation. However, this would require real-time three-axial attitude data. As a possible solution, this paper will review the potential of GNSS-based attitude determination systems with reference to HAP stations. In particular, it will be shown how the use of a particular class of low multipath and lightweight antennas can provide a high degree of accuracy without altering the avionic ballast.     

Hyper Redundancy for Accuracy Enhancement in Automated Close Range Photogrammetry

A generic network design in close range photogrammetry is one where optimal multi-ray intersection geometry is obtained with as few camera stations as practicable. Hyper redundancy is a concept whereby, once the generic network is in place, many additional images are recorded, with the beneficial impact upon object point precision being equivalent to the presence of multiple exposures at each camera position within the generic network. The effective number of images per station within a hyper redundant network might well be in the range of 10 to 20 or more. As is apparent when it is considered that a hyper redundant network may comprise hundreds of images, the concept is only applicable in practice to fully automatic vision metrology systems, where it proves to be a very effective means of enhancing measurement accuracy at the cost of minimal additional work in the image recording phase. This paper briefly reviews the network design and accuracy aspects of hyper redundancy and illustrates the technique by way of the photogrammetric measurement of surface deformation of a radio telescope of 26 m diameter. This project required an object point measurement accuracy of σ  = 0·065 mm, or 1/400 000 of the diameter of the reflector.     

用于多频电磁波测井的负阻抗变换式有源接收天线

本文对用负阻抗变换电路同小圆锥螺旋天线相结合,构成的有源接收天线进行了理论分析,并给出了该有源天线稳定工作的条件。结果表明,用该方法设计的有源接收天线具有较宽的频带、较高的灵敏度和较小的尺寸。是多频电磁波测井较理想的接收天线。     

用于多频电磁波测井的圆锥螺旋式有源接收天线

对用负阻抗变换电路同圆锥螺旋天线相结合，构成的有源接收天线进行了理论分析。并给出了该有源天线稳定工作的条件和设计原理。结果表明，用该方法设计的有源接收天线具有很宽的频带、较高的灵敏度和很小的尺寸，是多频电磁波测井较为理想的接收天线。     

流动VLBI天线系统噪声温度及天线效率测量

我国自行研制的第一套流动VLBI系统——DCW—01型流动VLBI测量仪，目前已在国家重大科学工程“中国地壳运动观测网络”中投入使用。在流动VLBI的观测试验中，天线系统噪声温度和天线效率是观测前系统调试和检测的两项重要内容。天线系统噪声温度是衡量流动VLBI观测系统内部噪声程度的特性指标；天线效率反映了天线系统对到达天线能量的刊用率，在很多计算公式中是一个很重要的参数。因此，精确地测量它们的值是进行相关处理和计算的前提。文中结合我国流动VLBI观测站的研制与建设，介绍了流动VLBI测量仪的天线及接收机系统，并详细阐述了其天线系统噪声温度和天线效率的测量。     

基于等价权抗差估计和线性规划的天线曲面拟合算法

现有天线曲面拟合算法均基于最小二乘法,难以消除多个粗差对拟合结果的影响。本文基于等价权抗差估计思想,利用线性规划计算残差初值,再进行选权迭代计算。通过算例,证明本文方法能较好地探查多个粗差,且计算结果精度更高。     

低剖面紧凑的圆盘加载单极子天线

本文介绍了一种低剖面小型化圆盘加载单极子天线.通过盘加载的方式,在中心频率5.8 GHz处,首先将单极子天线的剖面从大约12.9 mm（0.25λ₀）降低到2 mm（0.039λ₀）,实现了低剖面的特性.加载在单极子天线上方的圆盘,尺寸大概为21 mm（0.41λ₀）,因此天线具有结构紧凑的特点.接着,为了使天线具有良好的匹配,在加载圆盘四周加入4个接地通孔,并且在馈电端口加入集总电感.最终,天线在中心工作频率5.8 GHz处实现了反射系数-15 dB的匹配性能.     

航天遥感立体测绘小卫星目标跟踪与角度测量

随着现代小卫星技术的不断发展成熟，利用该技术为地球观测服务将成为一件远景可观，意义深元的事情，文中针对舆型航天遥感立体测绘微小卫星的需求，结合单脉冲测角原理给出了航天遥感测绘小卫星地面站面线系统的整体分析与设计。     

探地雷达天线方向特性探讨

利用电磁波的传播特点,对元天线、对称振子及其天线阵辐射电磁波的方向性做进一步的探讨,并分析各因素对其辐射方向性的影响。     

地下钻杆透层天线

对于有耗分层媒质中的垂直透层天线，建立了Ｈａｌｌｅｎ积分方程分析法的一般理论以及求取地面电场和电压的计算方法．作为应用实例，给出了地下３层媒质中钻杆天线上的电流积分方程，并对典型的地质参数进行了数值计算．所得结果和结论，与已知的理论结果和实验规律吻合。