Evaluation of cable tension sensors of FAST reflector from the perspective of EMI

The active reflector of FAST(five-hundred-meter aperture spherical radio telescope) is supported by a ring beam and a cable-net structure,in which nodes are actively controlled to form series of real-time paraboloids.To ensure the security and stability of the supporting structure,tension must be monitored for some typical cables.Considering the stringent requirements in accuracy and longterm stability,magnetic flux sensor,vibrating wire strain gauge and fiber bragg grating strain gauge are screened for the cable tension monitoring of the supporting cable-net.Specifically,receivers of radio telescopes have strict restriction on electro magnetic interference(EMI) or radio frequency interference(RFI).These three types of sensors are evaluated from the view of EMI/RFI.Firstly,these fundamentals are theoretically analyzed.Secondly,typical sensor signals are collected in the time and analyzed in the frequency domain,which shows the characteristic in the frequency domain.Finally,typical sensors are tested in an anechoic chamber to get the EMI levels.Theoretical analysis shows that Fiber Bragg Grating strain gauge itself will not lead to EMI/RFI.According to GJB151 A,frequency domain analysis and test results show that for the vibrating wire strain gauge and magnetic flux sensor themselves,testable EMI/RFI levels are typically below the background noise of the anechoic chamber.FAST finally choses these three sensors as the monitoring sensors of its cable tension.The proposed study is also a reference to the monitoring equipment selection of other radio telescopes and large structures.     

红外/微波波束合成器近场均匀性分析

针对矩量法（MoM）计算电大尺寸介质近场分布的低效率,提出使用口径场积分法（AFIM）分析红外/微波波束合成器近场均匀性,对比表明,AFIM相对MoM偏差小于10%,计算时间从数小时缩短至数秒.以电场分布曲线的标准差为均匀性指标,计算表明波束合成器近场均匀性关于D2/λL成负幂函数关系（D为波束合成器口径,L为近场距离,λ为波长）.将该负幂函数用于波束合成器外形尺寸优化,优化结果通过MoM进行验证,相对偏差小于10%.      

像平面照度在影视教学中的应用

在影视教学中，正确引入像平面照度公式，有利于学生牢固掌握基础知识，培养动手能力，提高专业素质．     

圆迹合成孔径雷达成像技术综述

圆迹合成孔径雷达(circular synthetic aperture radar, CSAR)由于具有亚波长量级的平面分辨率、三维成像潜力以及全方位观测能力等条带合成孔径雷达不可比拟的优势,在遥感测绘、灾害监测与评估、森林作物资源管理、战场目标侦察等领域具有广阔的应用前景。本文首先给出了CSAR的信号模型,并分析了其成像特点,然后较为全面地分别对国外和国内CSAR系统和试验的研究进展进行了综述,接着通过对CSAR成像算法、运动补偿、三维成像等成像技术现状的详细分析,总结归纳了CSAR成像技术当前仍然存在的问题,最后对CSAR成像技术进行了总结,并对CSAR未来发展进行了展望。     

Multi-baseline phase unwrapping algorithm for INSAR

A novel multi-baseline phase unwrapping algorithm based on the unscented particle filter for interferometric synthetic aperture radar(INSAR) technology application is proposed.The proposed method is not constrained by the nonlinearity of the problem and is independent of noise statistics,and performs noise eliminating and phase unwrapping at the same time by combining with an unscented particle filter with a path-following strategy and an omni-directional local phase slope estimator.Results obtained from multi-baseline synthetic data and single-baseline real data show the performance of the proposed method.     

基于MN-MEA算法的无人机载SAR相位误差补偿处理

无人机载合成孔径雷达(synthetic aperture radar, SAR),在成像中更容易受到运动误差的干扰,造成图像质量下降。利用三维空间坐标系的斜距方程分离,可以为无人机载SAR成像提供更多的信息，但该方法并未考虑无人机载SAR成像中的运动误差补偿问题。针对无人机载机动SAR成像的相位误差补偿问题,进行相关研究。结合子图像划分,提出了基于迭代分块处理和误差相位初值模型的改进牛顿最小熵(modified Newton minimum entropy, MN-MEA)相位误差补偿算法,进一步校正了残余空变性误差和运动误差,改善成像质量。     

SAR imagery coding based on blocking high frequency energy matching

A new fractal image compression algorithm based on high frequency energy (HFE) partitioning andmatched domain block searching is presented to code synthetic aperture radar (SAR) imagery. In the hybridcoding algorithm, the original SAR image is decomposed to low frequency components and high frequencycomponents by wavelet transform (WT). Then the coder uses HFE of block to partition and searchthe matched domain block for each range block to code the low frequency components. For the high frequencycompone...     

基于量子算法的逆合成孔径雷达稀疏成像方法

经典稀疏重构算法的计算复杂度较高，易导致雷达系统面对较大规模雷达回波数据时实时成像处理能力不足。针对这一问题，将量子算法应用于逆合成孔径雷达成像的稀疏信号处理中，为雷达稀疏成像带来量子计算短时间内处理大规模数据的优势。首先，根据逆合成孔径雷达稀疏成像的经典算法，分析匹配滤波、稀疏重构等经典算法的量子化方法，建立经典算法与量子算法之间的映射关系；其次，在确定相应量子算法及步骤关系的基础上，构建能够实现稀疏成像经典算法功能的量子线路，提出基于量子算法的逆合成孔径雷达稀疏成像方法；最后，根据构建的量子线路，结合雷达回波信号，制备相应的量子态，输入到量子线路中获得成像结果。仿真实验表明：相较于经典稀疏成像算法，基于量子算法的稀疏成像方法能够在保证成像质量的同时，大幅降低雷达成像处理数据的计算复杂度。     

车载Ka-SAR距离向自适应DBF方法

毫米波合成孔径雷达（Ka-SAR）进行俯仰向数字波束形成（digital beam forming,DBF）车载地面验证时，由于车载高程较小使得成像区域地形起伏不可忽略。采用传统扫描接收（scan on receive, SCORE）算法获得的DBF加权系数会存在误差，使合成波束方向图偏离理想状态，降低系统性能。针对上述问题，本文提出了一种基于多通道SAR的自适应距离向DBF处理算法，对多通道数据进行干涉处理，并通过滤波提取干涉相位，自适应生成加权系数，提高了接收增益。该自适应算法获得的加权系数精度较高，具有处理流程简单、运算量小、便于实时处理的特点。最后，基于仿真和车载实验数据成像，验证了该算法的有效性。     

基于乘积调制的SAR灵巧干扰方法

噪声乘积调制不仅能获得雷达处理增益, 还能自动瞄准信号频率, 被广泛应用于目标突防等重要作战场景。借鉴其基本原理, 提出了对合成孔径雷达(synthetic aperture radar, SAR)的乘积调制灵巧干扰方法, 在不改变截获信号调制流程的基础上, 仅通过线下模板设计, 即可灵活选择压制或欺骗的不同干扰效果。首先建立了干扰信号模型, 推导分析了其成像结果, 继而详细阐述了调制模板的生成方法; 最后, 从理论上分析了干扰的性能情况。仿真结果表明, 所提的干扰方法能仅通过设计不同的调制模板即可实现场景压制或虚假目标欺骗, 干扰效果对侦察精度的依赖性较小, 干扰调制流程简单高效, 便于工程实践。