基于孔径平滑效应的无线光通信接收孔径的设计

基于激光大气湍流传输理论,讨论了光强闪烁对无线光通信接收性能的影响。从孔径平滑效应出发．提出了一种结合信噪比、误码率、孔径平滑3方面来考虑接收孔径尺寸的设计方法。该设计方法克服了传统只考虑孔径平滑效应来设计接收孔径不准确的缺点,从而为设计接收孔径尺寸提供理论依据。用MATLAB对参考文献中的实验数据进行数值模拟,结果表明：在此实验数据下BER〈10^-6时,当SNR0为30dB时,最优接收孔径为4cm,当SMR0为35dB时,最优接收孔径为3cm。     

接收孔径对无线光通信误码率性能影响分析

接收孔径可以有效地改善无线光通信链路的误码率性能.文章从孔径平均效应出发,比较了圆环接收孔径和圆形接收孔径的平均因子差异,进而分析了其对通信系统误码率的影响.仿真结果表明:当接收孔径D＜8cm时,两种形状的孔径平均因子存在较大差异,误码率的相时误差较大;而当D≥8 cm时,两种形状的孔径平均因子基本相等,误码率的相对误...     

源象闪烁孔径平滑与积分光强起伏概率

研究了复振幅满足椭圆高斯分布散射光场时的孔径平滑效应,得到了相应的孔径平滑因子.从理论上分析了有限孔径检测到的孔径积分光强起伏分布,结果表明当检测孔径内包含的相关散斑面元数足够大时,闪烁满足对数正态分布,与已有实验观测结果一致.     

16km水平激光链路孔径接收条件下信号衰落规律

为了研究远距离水平激光链路接收光强起伏的统计特性,进行了16km水平激光传输实验.介绍了大气闪烁的对数正态与伽马-伽马分布模型,根据实验结果分析了孔径接收下信号衰落的统计规律.实验结果表明:伽马-伽马与对数正态分布在较大孔径接收时都能较好地分析远距离传输的光强起伏分布,而且分别是信号性能的上限与下限.采用何种模型要根据实际接收情况,较小孔径接收时,采用伽马-伽马较为准确.由于孔径平均效应和闪烁饱和效应,10-6衰落几率条件下16km激光链路孔径接收衰落阈值只有6～10dB.     

湍流外尺度对光闪烁孔径平滑的影响

基于包含湍流内、外尺度和高波数跃变的变形Andrews折射率谱从理论上分析了平面和球面波大气闪烁孔径平滑效应,得出了弱湍流起伏区无限平面波闪烁平滑因子解析关系和球面波孔径平滑因子内插关系.结果表明,在分析孔径平滑效应时应该考虑湍流外尺度的影响.作者采用变形Andrews折射率模型所得结果与采用Kolmogorov谱计算值间有明显差别.     

孔径匹配对中继镜系统上行传输影响的模拟与分析

利用激光大气传输四维程序,建立了双望远镜中继镜系统上行传输模型,研究了孔径匹配对中继镜系统上行传输的影响。选择去除畸变相位后的接收光场的远场峰值功率密度作为中继镜系统上行传输的性能指标,通过光束在真空中传输的计算,得到了接收口径一定时不同发射口径对应的最优发射焦距,并对不同发射功率激光在大气中上行传输的情况进行了模拟计算。结果表明,当接收孔径一定时,随着发射孔径的增大,最优发射焦距减小;增大发射孔径,可以增大临界发射功率;当发射功率较小时,在一定发射口径范围内,发射口径的变化对中继镜系统上行传输的性能指标影响不大,当发射功率较大时,增大发射口径可以有效提高中继镜系统上行传输的性能指标。     

下行传输孔径接收光强起伏的统计特性

为了研究星地下行激光链路接收光强起伏的统计特性,进行了恒星观测实验,分析了下行传输孔径接收下实际接收光强起伏的归一化方差、概率密度和闪烁频谱,并讨论了接收端瞄准偏差对接收光强的影响和星地下行大气信道的传播特性。实验结果表明,在下行传输孔径接收的条件下,天顶角从0°增至55°时接收光强的归一化方差从0.015增到0.102,不同天顶角下的接收光强起伏概率分布均服从对数正态分布,稳定大气条件下闪烁频谱的高频幂指数为-5/3,不稳定大气条件下为-11/3。     

大气光通信中大孔径接收性能分析与孔径尺寸选择

大孔径接收是克服大气光通信中大气湍流影响的有效途径之一.在有限孔径接收光强起伏理论基础上,建立了平均信噪比与无湍流影响时的探测器输出信噪比、孔径平均因子以及光强起伏方差之间关系的数学模型,并给出了系统误码率计算公式.通过数值计算得出了在给定误码率(BER)设计指标时,不同大气湍流参数条件下,接收孔径直径与无湍流影响时的探测器输出信噪比之间的关系曲线.     

基于子孔径分析的极化散射机理研究

在用极化sAR数据研究极化散射机理时,利用的是大量不同方位观察角度下接收的目标散射数据,但通常极化散射特性随方位角的变化并未被考虑。文中提出利用子孔径分析方法研究极化散射机理。子孔径是在不同的方位观察角度下．对整个场景的响应。用子孔径方法分析高分辨率极化sAR图像,可以突出全孔径中雷达后向散射的瞬时变化．因此可用于各向异性特征和非平稳目标的检测。最后利用丹麦EMISAR获取的L波段极化SAR全孔径图像数据进行仿真验证,提出了一种计算相对标准偏差的方法来检测非平稳目标。     

湍流大气中孔径平均对有效信噪比的影响分析

从孔径平均效应出发,首先建立高斯光束条件下的有效信噪比模型,并结合模型中的孔径平均因子,详细介绍了高斯光束下的孔径平均效应模型,在此基础上,通过仿真实验对比分析了不同湍流强度下有效信噪比随孔径尺寸的变化趋势,结果发现：随着孔径尺寸的不断增加,有效信噪比逐渐变大,说明孔径平均效应可以有效抑制大气湍流对通信系统的影响。     

Impulse responses of aperture antennas with arbitrary aperture distributions

On the basis of the equation of the Fresnel-Kirchhoff scalar diffraction field, it is shown that the impulse responses of parallel-fed aperture antennas of arbitrary configuration with arbitrary aperture amplitude distributions and those of end-fed rectangular aperture antennas with arbitrary aperture amplitude distributions can all be expressed by the aperture amplitude distributions, and that the impulse responses of rectangular aperture antennas with separable aperture distributions and those of circular aperture antennas with circularly symmetric distributions are special cases of the above general ones.     

合成孔径激光雷达

介绍了一种新体制的激光成像雷达棗合成孔径激光雷达,对它的成像基本原理、国内外研究进展和回波信号基本处理方法作了描述,介绍了它的关键技术和国内外技术差距,指出其在军事、科学研究、工业生产中都有广阔的应用前景.     

Earth-rotation aperture synthesis

Resolution for radio astronomy in the order of 1" is necessary for the study of distant radio galaxies and quasars, for detecting faint sources, and for the mapping of clouds of hydrogen and other molecules. To obtain these resolutions many new or planned radio instruments use arrays of moderate size radio telescopes to synthesize large physical apertures. These instruments are generally composed of one or several linear arrays and utilize the rotation of the earth to change the relative orientation of the array and the radio source. The techniques used for earth-rotation aperture synthesis are discussed. The response of a two-element interferometer and the geometry associated with earth-rotation synthesis are reviewed; the current and proposed designs for these instruments and their performance are described; and, finally, the inversion methods for determining the angular power distribution of a radio source from the array response (visibility function) are outlined.     

Estimating aperture efficiency

It is shown that for a wide class of aperture distributions, the aperture efficiency can be related to the ratio between the beamwidth of this distribution and that of the uniform one. A heuristic rule for estimating the aperture efficiency of elliptic and rectangular tapered apertures is introduced. It is shown that, if the beamwidth is given (i.e., the aperture size is unconstrained), the maximum directivity is provided by a tapered, rather than uniform amplitude distribution.     

Synthetic aperture radar

A short introduction to the background and theory of synthetic aperture radar (SAR) imaging is given. Some of the key issues in SAR design are discussed and possible future developments involving SAR operation with phased arrays are suggested     

大口径光学元件透射率全口径检测系统研究

提出了利用双光束分光光度和扩束系统相结合方法实现光学元件透射率全口径检测,建立了相应的检测系统,通过实验对系统的透射率检测精度进行分析和验证。结果表明,系统透射率检测精度优于±0.05%,并具有很好的重复性,能够用于ICF系统中大口径光学元件透射率的高精度、全口径检测。     

方形孔径自由曲面反射式系统装调技术研究

针对方形孔径自由曲面反射系统,构造方形域上正交多项式用于波前解析,得到方形孔径系统波像差系数。在计算机辅助装调阶段,为确保装调结果准确,用方形域上正交多项式和光学设计软件来建立系统的灵敏度矩阵,结合自准直干涉法得到的多个视场得波像差来求解系统失调量;在多次迭代后得到系统平均RMS为0.164 1(632.8 nm)实测系统平均传递函数达到0.453 4的理想结果;证明该装调方法正确性,并适用于其他形状孔径自由曲面离轴反射系统式系统装调。     

小孔径采样在大口径系统主镜装调中的应用

为了满足大口径光学—红外系统主镜的检测装调,引入了小孔径采样方法对于系统主镜的低阶误差进行分析,进而对系统的装调进行指导。随着光学-红外系统的口径加大,由于检测成本等原因,之前在装调时使用的与制造过程中相同的检测方法已经不再适用。本文首先对于小孔径扫描的基本原理做出了介绍,之后提出了实现本文方法的硬件结构,最后通过数值仿真来验证本文方法的正确性与可行性。对于大口径光学-红外系统主镜的装调检测有着较好的指导作用。     

Optimum aperture monopulse excitations

A unified formulation of the optimization of monopulse antenna performance indices for a specified sidelobe envelope function and/or specified nulls of the pattern is presented. The performance indices considered are beam efficiency, gain factor, and angular sensitivity factor of rectangular and circular apertures. The unconstrained optimization of beam efficiency result in an integral equation, the solutions of which are prolate spheroidal wave functions for rectangular aperture and hyperspheroidal wave functions for circular aperture. These functions reduce, respectively, to Legendre and Zernike polynomials in the case of gain factor and angular sensitivity factor. The double orthogonality properties of these eigenfunctions are used for constrained optimization. The results obtained by this technique for the near-in sidelobes constrained at a uniform level are shown to be in agreement with the earlier works. The method is applicable for other aperture surfaces such as elliptical, ellipsoidal, and spherical.     

Circular aperture distribution functions

Hansen's recently described one-parameter distribution for the circular aperture and Taylor's earlier one-parameter line source distribution produce radiation patterns that are members of a broader two-parameter family originally described by Bickmore and Spellmire. As Hansan points out, his distribution is a compromise between various conflicting desirable characteristics. Among other things, determination of the true optimum pattern for a given application requires careful consideration of the relative importance of the peak sidelobe specification and the level of the more remote sidelobes.