O21测量中S21的含义是什么

嗨Sharaf，校准程序在N4375B用户指南的第6章中有所描述。
通常，顺序是首先选择扫描参数，如开始和停止频率等。然后进行电气校准。
由于N4375B内部通过开关路由RF功率，因此有第6章所述的用于进行校准的特殊连接。完成此校准后，可以启动所需LCA测量的宏（OE，EO或OO）
。
这将包括LCA发射器和/或接收器的适当校准数据。
它还允许为任何其他适配器进行额外的重新嵌入。
LCA测量OE的光学到电学转换的频率依赖性或EO测量的电学到光学的频率依赖性，包括器件的电侧的RF反射。
对于OO测量，通常进行用户校准以表示零插入损耗。
然后可以插入光学装置，结果给出了调制到光学载体上的RF信号的衰减。
由于结果以dBe给出，例如3dBo的光衰减将使S21结果减少6dBe。
如果设备没有一些过滤功能，通常不会有明显的频率依赖性。
（多模光纤，可以使用N4376D测量，由于差模分散，可能会显示带宽限制。）除了用户指南之外，本应用笔记还对测量原理有了很好的概述。
http://literature.cdn.keysight.com/litweb/pdf/5989-7808EN.pdf



     以下为原文

  Hi Sharaf,
The calibration procedure is described in Chapter 6 of the User Guide for the N4375B.
In general, the sequence is to first select the sweep parameters, like start and stop frequency etc.
Then an electrical calibration is made. Since the N4375B routes the RF power internally with switches, there are special connections for making the calibration, as described in Chapter 6.
After this calibration is finished, the macro for the desired LCA measurement, (OE, EO or OO) can be started. This will include the appropriate calibration data for the LCA transmitter and/or receiver. It also allows additional deembedding for any other adapters.
The LCA measures the frequency dependence of the optical to electrical conversion for OE or electrical to optical for EO measurements, including the RF reflection of the electrical side of the device.
For OO measurement, a user calibration is usually made to represent zero insertion loss. Then an optical device can be inserted and the result gives the attenuation of the RF signal that is modulated onto the optical carrier. Since the results are given in dBe, an optical attenuation of 3dBo for example, will give 6dBe reduction of the S21 result. If the device does not have some filtering function there will usually not be significant frequency dependence. (Multimode fibers, which can be measured with the N4376D, can show bandwidth limitations due to differential mode dispersion.)
Besides the User Guide, this application note gives a good overview of the measurement principles.
http://literature.cdn.keysight.com/litweb/pdf/5989-7808EN.pdf

非常感谢我测量了10 dB衰减器的参数我开始使用电校准进行光学校准，然后测量S21曲线是平坦的，光功率是-10.3 dBm（输入0 dBm），这很好问题是S21在
-8.6 dB，我不知道为什么它显示这个值我尝试将前向RF功率从5改为0但它没有改变任何东西即使它是dB电气，它应该显示-20dB或某物（双倍光学
价值）有什么解释吗？
提前致谢



     以下为原文

  Thank you very much

I measured the parameters of a 10 dB attenuator

I started with electrical calibration the optical calibration then measurement

S21 curve was flat and the optical power was -10.3 dBm (input 0 dBm) which is good

the problem is that S21 is at -8.6 dB and I don't know why it shows this value

I tried changing the forward RF power from 5 to 0 but It didn't change anything

Even if it is dB electrical, it should show -20dB or something (double the optical value)

Is there any explanation?

thanks in advance

您是否进行了O / O用户校准，如用户指南（2008年第2版）中的第105-106页？
您是否使用与衰减器相连的相同光纤制作？
当您进行校准，然后直接测量而不重新连接时，S21应接近0dB，因为O / O测量仅显示用户校准和测量之间的电平变化。
如果然后在路径上增加10dB的光衰减仅导致S21的微小变化（如-8.6dB），则表明在进行用户校准时光学连接不好。
在为用户校准选择“无”后，您还可以通过对用户校准路径进行O / O测量来检查。
如果与工厂校准相比，显示的值显着低于0dB，则在某些连接处会断电。
这与第40页上的验证测试类似。（只是为了确保：请注意前面板连接器是带角度的连接器，因此必须使用带角度的连接器跳线。如果这些是FC / APC，还要确保它们具有窄键控
连接器接口有一个很小的间隙（81000NI）。如果你使用的是原装光纤跳线就是这种情况。）



     以下为原文

  Did you make the O/O User Calibration, like on pages 105-106 in the User Guide (2nd Edition 2008)?
Did you make that with the same fibers that were then connected to the attenuator?

When you make that calibration, and then measure directly without reconnecting, the S21 should be close to 0dB, since the O/O measurement is just showing the change in level between the User Cal and the Measurement.
If then adding 10dB  optical attenuation to the path causes only a small change in S21 (like the -8.6dB) it suggests that the optical connections were not good while making the User Cal.
You could also check that by making an O/O measurement of your User-Cal path after selecting "None" for the User Calibration. If that shows values significantly lower than 0dB compared to the factory calibration, then power is being lost at some connection. This is like the verification test on page 40.
(Just to be sure: note that the front panel connectors are angled connectors, so angled connector patchcords must be used. If these are FC/APC, also be sure that they have narrow keying if the connector interface has a narrow gap (81000NI). That would be the case if you are using the original fiber patchcords.)

我在哪里可以找到第二版用户指南？
谢谢



     以下为原文

  where can i find the 2nd edition user guide?

thanks

N4375B页面上似乎缺少这个链接。
这应该工作。
http://literature.cdn.keysight.com/litweb/pdf/4375B-90A02.pdf使用当前N4375D的最新版本也应该没问题。



     以下为原文

  The link seems to be missing on the N4375B page. This should work.
http://literature.cdn.keysight.com/litweb/pdf/4375B-90A02.pdf 
It should also be fine to use the newest edition for the current N4375D.