反射损耗的测量与改善措施

反射损耗是衡量电视设备终端阻抗匹配程度的一项重要指标。设备两端匹配良好,可以把反射的能量全部吸收,或者说对反射的能量损耗很大。所以,反射损耗愈大愈好。当图象信号源、卫星电视接收设备、传输电缆、有线电视网络、彩色监视器等接口有阻抗失配现象时,都会产生反射。轻者波形失真,重者会引起非常显著的轮廓效应或单个及多个重影。因此,反射损耗的测量显得尤为重要。     

视频反射损耗测试方法介绍

本文介绍了视频反射损耗对电视图像的影响及改善反射损耗的一般措施，详述了视频反射损耗的具体测试方法，并对不同的方法进行了分析比较。     

光时域反射仪在工程测量中的几个问题

在光缆线路的施工维护中,常用光时域反射仪提高测量光缆长度、光接头损耗的精度,采用选定准确的折射率和换算系数,选拔好的动态范围与脉冲宽度,可减小盲区效应,增大光缆长度测量范围。（ｅｄ）     

光时域反射仪在工程测量中的几个问题

在光缆线路的施工维护中,常用光时域反射仪提高测量光缆长度、光接头损耗的精度,采用选定准确的折射率和换算系数,选拔好的动态范围与脉冲宽度,可减小盲区效应,增大光缆长度测量范围。     

测回波损耗应注意测试电桥的输出电平

测回波损耗 (与驻波比可以通过计算互得 )一般用长线法或电桥法两种方法。其中用电桥法还可以同时测得幅频特性 ,因而得到广泛使用。用驻波比电桥测无源设备一般没有什么问题 ,只须注意扫频仪的衰减不要过大 ,而测有源设备时则需要扫频仪的输出 (通过衰减器 )不能过大也不能过小。比如 ,当测放大器的输入端回波损耗时 ,扫频仪的衰减过小 ,被测放大器的输入电平过高 ,就会使得被测放大器输入级工作在饱和状态。而衰减过大 ,驻波比电桥内的检波二极管 (若系这种结构 )将会工作在截止状态。上述两种状态都会产生较大的非线性失真 ,都给人以匹配…     

基于光时域反射技术的回波损耗测量

介绍了几种光回波损耗的测量原理和测量方法.针对大量光纤器件的回波损耗实际测量需求,提出了基于光时域反射技术的解决方案,并给出了该方案实现所需的一些关键技术和实用电路.     

浅析光纤连接器插入损耗测试

本文介绍了光纤连接器的基本结构,阐述了导致光纤连接器产生插入损耗的主要原因,对实际测试和试验中发现的问题进行了分析,给出连接器测试及试验的建议.     

Measurement of Microwave Loss Tangent by Means of Microwave Resonator Bridge (Short Papers)

A new cavity method of measurement of microwave loss tangent of a low-loss material is described. The method consists of the comparison of the reflection coefficient of the resonator filled with dielectric with the reflection coefficient of the reference resonator by means of microwave resonator bridge. Basic theoretical relations of a simplified resonator bridge are derived, a fundamental scheme of the measuring set is given, and some results of verified measurements presented. The obtained results confirm the suitability of the proposed method, especially for measuring low-loss dielectric materials, since the principle of comparison renders the method highly sensitive to small parameter differences of the resonator brought about by the measured sample.     

Comments on "Measurement of Microwave Loss Tangent by Means of Microwave Resonator Bridge" (Letters)

In the above paper, Kneppo and Weis claim that the microwave resonator bridge (MRB) is a new and highly sensitive method for measuring dielectric losses of materials. Contrary to their belief, the principles of measurement are not new but have already been reported in [1] and [2]. Especially, the system arrangement described in [2] is the same as that of MRB, except that the former uses a shutter in tandem with a matched termination as a reference load of the bridge, while the latter uses a reference resonator. Thus the point in question is whether or not this replacement of the reference load improves the sensitivity of the bridge.     

计及地面反射且考虑大气折射和地球凸起影响时的双刃峰绕射场

根据Ｆｒｅｓｎｅｌ—Ｋｉｒｃｈｈｏｆｆ原理，得到了计及地面反射时的多刃峰绕射场的一般表达式，在考虑大气折射和地球凸起影响的同时，导出了双刃峰绕射场的具体公式。得到的八射线场表达式简洁且物理图象清晰，便于工程技术中应用。     

对机械波半波损失现象的物理解释

机械波的半波损失现象长期困扰着科学工作者,对于机械波的半波损失现象虽然有数学证明,但证明过程多偏重于数学推导,大都缺乏明确的物理图像。文中根据介质分界面处的边界条件,试图用物理的方法来解释机械波的半波损失现象,以期对半波损失现象给出一个清晰的物理图像。文中还讨论了机械波在固定端和自由端处的反射和透射。     

Analysis of the Stability in a Gyrotron Traveling Wave Amplifier with the Reflection at Output Port

Based on the linear theory of gyrotron traveling wave amplifier (gyro-TWA) and the boundary condition, the model of the gyro-TWA with the reflections at the output port is established. The influence of the reflections on the wave gain rate, the back wave starting length and the back wave starting current for a Ka band TE₀₁ gyro-TWA at fundament is analyzed. The simulating results show that the increased reflection may lower its stability to some extent.     

The Measurement of Complex Reflection Coefficient by Means of a Five-Port Reflectometer

A detailed analysis of the five-port reflectometer is presented in this paper. The possibility and application limitation of using a five-port to measure complex reflection coefficients is discussed and the related design consideration is derived. From the poiut of view of minimum measurement error, an optimized, multi-octave five-port circuit is suggested and realized by ordinary microwave integrated circuit technology. Some measurement results are reported to prove the above analysis and design consideration.     

位敏探测器表面反射损耗的优化

本文通过计算SiO2单层以及SiO2和Si3N4组成的双层减反膜对不同波长的反射率,给出了位敏探测表面反射损耗的优化。     

5G系统部分频段电波穿透损耗对比测量与室内覆盖分析

5G系统中Sub 6 GHz和毫米波频段的综合结合应用是提供优质覆盖的关键,但某些频段易被障碍物遮挡,穿透性不足,为解决此问题,对典型建筑材料,如钢筋混凝土承重墙、单向透明玻璃、8 cm干燥石膏板非承重墙、干燥木门及组合物等的电波穿透损耗进行研究.基于测量的分析表明:5G毫米波从室外宏站覆盖室内是困难的,同时由于无源室...     

菲涅尔反射对光纤连接器插入损耗的影响

光纤连接器在研磨完成后,纤芯端面的3D图通常显示为凹陷,即在跳线两两对接时,两光纤端面间会存在空气间隙。当光经过此光纤连接器时,在两个端面之间必定产生菲涅尔反射。基于菲涅尔反射理论,分别讨论了在计入干涉和不计干涉两种情况下光纤连接器的插入损耗,并绘制了不同空气间隙厚度时的插入损耗曲线,解释了Telcordia GR-326-CORE Issue3把光纤凹陷限定在50nm之内的实际意义。