TRL混乱消除一劳永逸

老谜语：“问：如果你把一条马的尾巴称为一条腿，那么一条马有多少条腿”;
“A：四;只因为你把尾巴称为一条腿，并不代表它是一条腿”。
如果你拨打42.5欧姆线路50欧姆，这并不意味着它是一个。
S参数是相对于定义的阻抗的反射的度量。
如果你拨打42.5欧姆线50欧姆，校准它，然后用42.5欧姆阻抗测量设备，它将在史密斯图表的中心显示为一个点，它的S11将为零。
如果测量50欧姆负载，则其S11为-21.8 dB。
（但是，如果你打开史密斯圆图上的标记，第一种情况下的阻抗将为50欧姆，第二种情况下的阻抗将为58欧姆）。
现在，如果您使用相同的标准，但将标准阻抗更改为42.5欧姆，则在测量与上述相同的标准时，将产生相同的S参数。
唯一的区别是史密斯图表标记将读取您期望的值（图表中心为42.5）。
例如，S21将是相同的，因为在每种情况下使用相同的阻抗标准实际值，并且S21是相对于完美线的传输的度量;
您可以根据标准设定完美线条的特征。



     以下为原文

  Old riddle: "Q: IF you call a horse's tail a leg, then how many legs does a horse have"; "A: Four; just because you call a tail a leg, doesn't mean it IS one".

If you call a 42.5 ohm line 50 ohms, it doesn't mean it is one.

S-parameters are a measure of reflection relative to a defined impedance.  If you call 42.5 ohm line 50 ohms, calibrate it, and then measure device with 42.5 ohms impedance, it will show up as a dot in the center of the smith chart and it's S11 will be zero.   If you measure a 50 ohm load, it will have an S11 of -21.8 dB. (However, if you turn on a marker on the smith chart, the impedance will read 50 ohms for the first case and something like 58 ohms for the second).

Now, if you use the same standards, but change the standard impedance to 42.5 ohms, it will yield the same S-parameters when measuring the same standards as above. The only difference is the smith chart markers will read the values you expect (42.5 for the center of the chart).

The S21, for example, will be the same because the same impedance standard actual value was used in each case, and the S21 is a measure of transmission relative to a perfect line; you set the characteristics of a perfect line with the standards.

乔尔博士，感谢你的另一个诙谐和真实的回应。
这帮了很多忙。
所以现在我的问题是，“校准参考Z0”与所有这些相关联？
我被E-Cal同轴50欧姆校准所破坏，所以我倾向于设置“这是我的S参数参考50欧姆阻抗”然后我可以玩得开心并改变PLTS中的端口阻抗并说“他们在这里
现在引用______ohms“。
简单易用。
但是当我用PCB板做TRL时，这就是我感到困惑的地方。
我们有LRM标准，使用500欧姆SMA到42.5欧姆PCB跟踪。
导致另一个500欧姆的SMA或开放的短路负载。
在TRL之后，它是“这是我的S参数参考?????欧姆”。
“校准参考Z0”在哪里发挥作用？
什么是校准参考Z0以及什么是正确的心态？
它和端口阻抗之间有什么关系吗？
谢谢，KTB编辑：KTB于2015年8月9日9:06 PM编辑：KTB于2015年8月9日下午11:06



     以下为原文

  Dr. Joel,

Thanks for another one of your witty and truthful responses. That helped a lot. So now my question is, where does "Calibration Reference Z0" tie into all of this? I'm spoiled from E-Cal Coaxial 50ohm Calibrations, so I tend to have the mind set of "Here are my S-Parameters Referenced to 50Ohm Impedance" then I can have fun and change port impedances in PLTS and says "Here they are now referenced to ______ohms". Easy and simple.

But then when I do a TRL with a PCB board, this is where I get confused. We have LRM standards using 50Ohm SMAs to 42.5Ohm PCB Traces. leading to another 50Ohm SMA or a open,short,load. After TRL, it's "Here are my S-Parameters Referenced to ????? Ohms". Where does "Calibration Reference Z0" play it's part here?

What is Calibration Reference Z0 and what's the right state of mind to have? Is there any relationship between it and the port impedance?

Thanks,
KTB

Edited by: KTB on Aug 9, 2015 9:06 PM

Edited by: KTB on Aug 9, 2015 11:06 PM

> {quote：title = KTB写道：} {quote}>我的问题是，“校准参考Z0”在哪里与此相关？
校准参考Z0是在cal之后表示S11 = 0的阻抗。
>但是当我用PCB板做TRL时，这就是我感到困惑的地方。
我们有LRM标准，使用500欧姆SMA到42.5欧姆PCB跟踪。
导致另一个500欧姆的SMA或开放的短路负载。
在TRL之后，它是“这是我的S参数参考?????欧姆”。
“校准参考Z0”在哪里发挥作用？
参考TRL的-ACTUAL-线阻抗。
校准Z0只是一个数字标签。
如果您将42.5欧姆线路称为50欧姆线路，您仍将拥有42.5欧姆线路;
S11将在4.25欧姆的DUT上等于零，但它将在50欧姆的标记上读出。
>>什么是校准参考Z0以及什么是正确的心态？
它和端口阻抗之间有什么关系吗？
>因此校准Z0（或系统Z0）是零反射标准的标称值。
过去，校准代码在校准期间和测量期间都会查看系统z0，但几年前我们改变了calkits的工作方式，因此在校准期间，校准引擎会查看校准z0以了解校准标准的值而不是系统z0
。
这需要支持你想要在一个端口上校准D欧姆50欧姆而在另一个端口上校准75欧姆的情况;
每个端口都可以拥有自己的calkit和预期的z0。
但是你想做什么？
你的DUT是42.5欧姆吗？
你想读取S11 = 0为42.5欧姆，还是50欧姆？
S参数不是不变的;
它们的值取决于参考Z0所述的值（相反，Z参数是DUT的不变特性）。



     以下为原文

  > {quote:title=KTB wrote:}{quote}
>my question is, where does "Calibration Reference Z0" tie into all of this? 
The calibration reference Z0 is the impedance that represents S11=0, after cal.
> But then when I do a TRL with a PCB board, this is where I get confused. We have LRM standards using 50Ohm SMAs to 42.5Ohm PCB Traces. leading to another 50Ohm SMA or a open,short,load. After TRL, it's "Here are my S-Parameters Referenced to ????? Ohms". Where does "Calibration Reference Z0" play it's part here?
Referenced to the -ACTUAL- line impedance of TRL.  The calibration Z0 is just a numeric label.  If you call the 42.5 ohm line 50 ohms, you will still have a 42.5 ohm line; S11 will equal zero on a DUT with 4.25 ohms, but it will read-out on the marker 50 ohms.
> 
> What is Calibration Reference Z0 and what's the right state of mind to have? Is there any relationship between it and the port impedance?
> 
So calibration Z0 (or system Z0) is the nominal value of the zero-reflection standard.

It used to be that calibration code looked at system z0 both during cal and during measurement, but years ago we changed how calkits worked so that during cal, the cal engine looks at calibration z0 to know the value of the cal standard rather than system z0.  This was needed to support cases where you wanted to do a calibration of a DUT with 50 ohms on one port and 75 ohms on another; each port could have it's own calkit and expected z0.

But what do you want to do? is your DUT 42.5 ohms?  Do you want to read the S11=0 for 42.5 ohms, or for 50 ohms?  S-parameters are not invariant; their value depends upon the value stated for reference Z0 (in contrast, Z-parameters are an invariant characteristic of the DUT).