激光测距系统的接收概率(下)

假设激光测距系统的发射光轴、接收光轴和系统跟踪轴彼此间不存在调整误差或调整误差可忽略,那么只要目标处于激光测距阈值角βT之内,接收目标反射回的激光能量就不小于接收阈值。     

浅析数字卫星电视接收天线

卫星电视接收天线就是安装有线电视前端机房外面空地或楼顶上,类似“大锅盖”状的设备。天线的作用是将来自地球同步卫星上的携带有数字电视信号的电磁波接收下来,通过反射将其聚焦于抛物面状天线的焦点上,进而传输给馈源。本文就卫星电视接收天线的种类、特点以及安装工作进行探讨。     

有线机顶盒射频接收测试

有线数字机顶盒是进行数字化转换的主要终端设备,在国内已经得到大规模的普及使用。有线数字机顶盒在入网时射频接收、视频指标、音频指标等都必须符合国家相关技术标准和网络要求后才能下发到网络中使用。其中射频接收测试包括调制方式测试、频率范围测试、频率捕捉范围测试、符号率范围测试、接收电平范围测试、解调门限测试、抗微反射（E／D）能力测试、抗频率抖动能力测试、抗同频单频干扰能力测试、抗脉冲干扰能力测试、抑制邻频道模拟信号干扰能力测试、抑制邻频道数字信号干扰能力测试、输入、输出反射损耗测试以及LNB环通输出频响测试和本振泄漏测试。     

如何调整卫星接收天线接收卫星信号

调整卫星天线接收卫星信号让人觉得是个很复杂的工作,难掌握,看到有人在调整卫星接收天线便想看个究竟,但是看过之后还是一头雾水。其实接收卫星信号并没有想象中的复杂,它非常简单,也很容易掌握。下面就介绍一下如何从实际角度出发来调整卫星接收天线,达到较好的信号接收效果。     

谈卫星电视节目接收效果与接收天线口径

卫星接收天线是卫星接收设备中的重要组成部分,要想接收到良好的卫星信号,接收天线很重要。人们往往认为要想收到良好的电视信号,只要增大天线直径,就一定能提高增益,得到满意的效果。其实不然,因为直径增大,半功率角减小,同时增加了调星难     

卫视接收全攻略——实战宝典

从卫星接收原理上来说，只要在卫星场强覆盖范围内，都能收到信号。但对于覆盖范围内某个具体接收点来说，则要求天线面接收到的卫星信号能完全聚焦反射到高频头的波导管内才能接收，这又只能是一个点即天线方位角、仰角的交叉点。这个点的直径范围，大约相当于高频头波导管的直径范围。     

卫星电视接收天线方向数据的计算和调整

接收卫星电视节目需要调整卫星接收天线的方向,使卫星电视转发器发射的电磁波经接收天线（抛物面）反射后聚集于馈源中心,才可能在高频头探针上感应出比较强的信号,这就需要调整正馈天线的主轴或偏馈天线的一副轴,指向要接收的卫星,轴指向由轴的仰角和方位角确定。卫星接收天线的仰角和方位角调整正确后还不一定在高频头的探针上感应出较强的卫星信号,还必须调整天线馈源的极化方向（高频头探针沿南北方向的叫垂直极化,高频头探针沿东西方向的叫水平极化）,使接收天线的水平极化与卫星转发器的水平极化方向一致,使接收天线的垂直极…     

CK股票接收系统

首先简要介绍了CK股票接收系统的构成,然后介绍了CK股票接收系统硬件的主要部分和软件的设计思路,最后对CK股票接收系统的市场前景作出了分析。     

DTH卫星电视广播的接收

本文介绍直接到户(DTH)卫星电视广播的接收,内容包括卫星电视接收天线、模拟和数字的综合接收解码器(IRD).     

单面卫星天线接收多颗卫星信号方案

单面卫星天线接收多颗卫星信号方案鹤壁市广播电视局孙贤明目前使用的卫星接收天线一般是一天线接收一卫星信号，如果能实现一接收天线接收多颗卫星信号，则将节省不少资金，减少占地面积。所以，一接收天线收多颗卫星信号有其经济价值和现实意义。尽管目前有几种利用一面...     

地形对基于波瓣分裂的米波雷达测高方法的影响

针对基于波瓣分裂的米波雷达“比相比幅”测高方法,研究地形对米波雷达测高的影响。说明不同介质的平坦地面反射系数,分析影响粗糙地面反射系数的各种因素,讨论不同地面反射系数对高度测量精度的影响。阐述地面几何反射点的计算方法,解释地面有效反射区的范围及其在测高中的应用,探讨漫反射信号产生原因及其对基于波瓣分裂测高方法的影响。     

激光引偏干扰中漫反射板假目标的布设方法

激光引偏干扰是一种对抗半主动激光制导武器的有效手段,漫反射板假目标是激光引偏干扰系统的标准配置设备,为了提高漫反射板假目标在激光引偏干扰中的诱偏效果,研究了漫反射板的布设方法。根据半主动激光制导武器的来袭威胁信息和漫反射板的反射特性,分析了漫反射板假目标的布设位置、漫反射面的朝向和多个假目标布设的具体要求,给出了量化的约束关系式,并指出了实际布设过程中的近似处理方法。研究结果对于漫反射板假目标的布设具有理论指导意义。     

Bragg gratings in multimode and few-mode optical fibers

Bragg gratings in optical fibers in multimode propagation are investigated experimentally and theoretically. Bragg gratings formed in optical fibers in multimode propagation show multiple reflection peaks or multiple transmission dips in the reflection or transmission spectra, respectively. For standard graded-index multimode fiber, the number of reflection peaks of a Bragg grating depends on excitation condition of propagating modes. The number of reflection peaks of a Bragg grating at around 1.55 μm is 19 for highly multimode excitation and 3-4 for lower order mode excitation. We analyze the phase-matching conditions of the propagating modes and identify half of the reflection peaks as the reflection to the same mode and the rest as the reflection to the neighboring modes. In dispersion-shifted fiber, a Bragg grating at around 0.8 μm in three-mode propagation shows three reflection peaks in the reflection spectrum. The temperature dependence of each reflection peak is similar to that of a conventional Bragg grating in single-mode fiber. Polarization dependence measured on a Bragg grating in multimode graded-index fiber is negligible. An advantage of Bragg gratings in multimode fiber (MMF) and the applications are discussed     

1维光子晶体中TM波的传输公式及其辨析

为了得到1维光子晶体中TM波的传输公式,采用传输矩阵的方法和电磁波的边界条件,推导出TM波在介质层中的特征矩阵及其反射系数和透射系数公式。结果表明,用TE波反射系数和透射系数公式做代换的方法不能得到正确的TM波的反射系数和透射系数公式;对推导出TM波的反射系数和透射系数公式进行了分析,由TM波的反射系数和透射系数公式得出的光强透射率和反射率满足能量守恒;并且推出的TM波反射系数公式不仅能够反映反射波与入射波的数量关系,且能够反映反射波与入射波的位相关系。这些结果对研究1维光子晶体中TM波的传输性质是有帮助的。     

Spurious reflection of space charge fields in TWTAs

The reflection of waves at the termination of a beam loaded traveling wave structure is considered. The presence of a bunched beam in the structure induces additional currents and voltages on the structure, which give rise to an additional reflection at the termination. This effect is first illustrated in a simple transmission line model, and then a formal field-based derivation for the reflection in a periodic structure is presented. Simple estimates for the magnitude of the reflection can be made based on the amplifier's Pierce parameter. Unlike the reflection due to a mismatched load, the spurious reflection due to the beam depends on signal power level. The spurious reflection can be simulated in large signal parametric codes, and examples of this are presented.     

Antispecular reflections in the backward-wave multimode systems

A specific backward-wave antispecular reflection from the interface of structures or media is analyzed. The reflection coefficients are calculated, and the dominant contribution of the alternative reflection is demonstrated. The supercritical (with respect to angle of incidence and frequency) total reflection and improper surface wave or edge wave in the plate are considered. It is demonstrated that the effect is similar to the Andreev quantum reflection of electrons (which is also alternative) and the elastic reflection of a mechanical top.     

Reflection coefficient (Schur parameter) representation for convex compact sets in the plane

We obtain a one-to-one relation between the shape and orientation of a convex compact planar set and a complex-valued reflection coefficient (Schur (1917) parameter) sequence, such that (1) the reflection coefficient magnitudes are less than or equal to one, (2) if any reflection coefficient has a magnitude equal to one, then all subsequent reflection coefficients are equal to zero, and (3) the first reflection coefficient is equal to zero. Three additional independent parameters specify the position of the set in the plane, and the size of the set (specifically its circumference). For a finite duration reflection coefficient sequence, if the last nonzero reflection coefficient has a magnitude that is less than one, then the boundary of the set is an infinitely differentiable convex curve. The boundary is a convex polygon if and only if the magnitude of the last reflection coefficient is equal to one; the number of sides of the polygon is equal to the index of the last reflection coefficient. Almost all planar convex compact sets have reflection coefficient sequences of infinite duration. Such sets can be accurately approximated with convex compact sets that are generated from relatively small numbers of reflection coefficients.     

基于MATLAB的两径模型仿真分析

针对无线电波远距离空—地传播,为了得到其在球面反射两径模型下的多径衰落特性,介绍了自由空间路径损耗和平面反射两径传播的数据模型。分析了球面反射两径传播的几何模型,并提出了用二分法确定几何反射点的位置,进而得到等效天线高度和扩散因子后用平面反射模型计算球面反射接收信号功率的方法。给出了基于矩阵实验室(MATLAB)编程的方法和仿真结果分析。     

花岗岩表面二向性镜面反射分量和漫反射分量的比较研究

偏振反射与二向性反射之间存在着一定的定量关系.通过对不同粗糙程度花岗岩表面偏振反射的测量,计算出它们表面二向性镜面反射分量与二向性漫反射分量的大小,从而定量分析了花岗岩表面粗糙程度对热点与非热点区域两种分量的影响情况.同时通过分析还发现,光线入射天顶角也会对两种分量的大小起到一定的影响,而这种影响的强弱是受到花岗岩表面粗糙程度的控制.     

传输线中信号反射的研究

现代高速电路设计中的信号完整性问题,尤其是过度的反射现象,常常造成严重的电路问题。研究了反射形成的机理,即阻抗突变引发信号反射,通过分析给出了减少反射的措施。由Altium Designer的信号完整性分析工具对设想进行了验证,仿真结果表明:适当的端接能大幅度改善传输线中信号的反射。