在LOAD状态下，Cal pod返回损失非常糟糕

我真的不知道这里的答案，所以希望乔尔或布拉德会说话......但是......我相信calpod的状态（打开，加载，短等）只是一个“建议”，
因为缺乏一个更好的词。
只要是已知数量，实际状态无关紧要。
从那里它可以计算系统的实际阻抗，并用它来纠正测量。
我知道，在查看calpod快速功能测试的简短内容时，我不得不使用低频，因为一个频率的短路看起来像另一个频率。
总之，我认为calpod不需要具有绝对的准确性，只需要重复性。



     以下为原文

  I don't really know the answer here, so hopefully Joel or Brad will chime in....but...
I believe the state of the the calpod (open, load, short, etc) is just a "suggestion", for lack of a better word.  The actual state does not matter as long as it is a known quantity.  From there it can calculate the actual impedance of the system and use that to correct the measurement.

I know in that in looking at a short for a quick functionality test of the calpod, I had to use a low frequency since a short at one frequency could look like an open at another.

In summary I believe the calpod does not need to have absolute accuracy, just repeatability.

> {quote：title = WDrago写道：} {quote}>全部，>>我正在尝试测量每个端口上带有calpods的2端口设备的回波损耗。
当我进行测量时，我将相对端口的calpod置于负载状态。
我希望calpod可以作为良好的终止，但事实并非如此。
我看到整个兴趣范围内有大约10到20分贝的回波损耗。
当我用实际负载替换calpod时，测得的回波损耗要好得多。
>>这是正常的吗？
calodods真的那么糟糕吗？
>您是否通过应用2端口校正来测量回波损耗？
如果是这样，你不应该手动改变相反端口calpod的状态。
非常简单地说，校正数学在计算校正的回波损耗时考虑了相对端口的终止。



     以下为原文

  > {quote:title=WDrago wrote:}{quote}
> All,
> 
> I'm trying to measure return loss on a 2 port device with calpods on each port. When I make the measurement I put the calpod on the opposite port into load state. I would expect that calpod to be acting as a good termination, but it is not. I see about 10 to 20 db return loss across the band of interest. When I replace the calpod with a real load, then measured return loss is much better.
> 
> Is this normal? Are the calpods really that bad?
> 


Are you measuring the return loss with 2-port corrections applied?  if so, you shouldn't manually change the state of the opposite port calpod.  very simplistically put, the correction math takes into account the termination of the opposite port when calculating the corrected return loss.

这很有道理，Daras。
谢谢。
测试3个或更多端口设备时我们该怎么办？
（我们有几个通过多路复用器连接到2端口pna-x的calpod。）我们如何获得不属于测量但连接到DUT以充当50欧姆负载的端口上的calpod？
我知道多路复用器中有负载，但我希望我们可以通过使用calpods作为负载来使这些负载更靠近DUT。
谢谢，-BillEdited：WDrago于2015年6月3日下午2:04



     以下为原文

  That makes a lot of sense, Daras. Thank you.

What do we do when testing a 3 or more port device? (We have several calpods connected to a 2-port pna-x through a multiplexer.) How do we get the calpods on the ports that are not part of the measurement but are connected to the DUT to act as 50ohm loads? 

I am aware that there are loads in the multiplexer, but I was hoping we could get those loads closer to the DUT by using the calpods as loads.

Thanks,
-Bill

Edited by: WDrago on Jun 3, 2015 2:04 PM

我不知道我的头脑中有多好的calpod负载，但我确信它提供了一个比通过路径更好的匹配（默认配置不使用时）。
用calpods和ECals实现的是我们不必复制完美的开启，短路和负载。
我们只需创建在史密斯圆图上合理分离并具有已知阻抗的状态。
所以我们称之为“负载”状态并不一定是一个好的负载（如机械宽带负载）。
然而，话虽这么说，你可以用2端口校正测量多路器件的程度在很大程度上取决于DUT本身。
让我们举一个3端口功率分配器的简单例子。
测量这种设备的最佳方法是使用3端口校准，但如果一次只能测量2个端口，那么良好的测量需要在未使用的端口上提供50欧姆的良好负载。
另一方面，如果你有一个多端口设备，不同路径之间存在一些内置隔离（如T / R模块），那么一个好的2端口测量不一定取决于良好的终端
未使用的端口。
因此，故事的寓意是，在理想的情况下，您应该始终使用n端口校准来测量n端口设备，但如果不可能，则使用calpod负载状态作为未使用端口的终端
不要让你的测量结果最差，实际上可能比不做任何事情要好一些。



     以下为原文

  I don't know off the top of my head how good the load of a calpod is, but I'm sure it presents a better match than it's thru path (the default configuration when it is not being used).  the thing to realize with calpods and ECals is that we don't have to replicate perfect opens, shorts and loads.  we simply have to create states that are reasonably separated on the smith chart and have a known impedance.  so what we call a "load" state isn't necessarily a good load (like a mechanical broadband load).

however, that being said, how well you can measure a mutliport device with a 2-port correction depends largely on the DUT itself.  let's take a simple example of a 3 port power divider.  the best way to measure such a device is to use a 3 port calibration, but if you can only measure 2 ports at a time, then a good measurement requires a good 50 ohm load on the unused port.  On the other hand if you had a multiport device, where there was some built-in isolation between the different paths (like a T/R module), then a good 2-port measurement wouldn't necessarily depend on a good termination of the unused port(s).

So the moral of the story is that in an ideal situation you should always use an n-port calibration to measure an n-port device, but if that is not possible, then using the calpod load states as a termination for the unused ports shouldn't make your measurements any worst and it may actually be a little better than not doing anything.

{quote：title = daras写道：}故事的寓意是，在理想的情况下，你应该总是使用n端口校准来测量n端口设备，但如果不可能，则使用calpod负载
作为未使用端口的终止状态不应该使你的测量结果最差，它实际上可能比没有做任何事情要好一些。{quote}我们发现负载状态比直通状态给我们带来更糟糕的结果。
（在直通状态下，DUT看到多路复用器内部的负载。）我们只是试图找出这是正常的还是我们做错了什么。
谢谢，-Bill



     以下为原文

  {quote:title=daras wrote:}So the moral of the story is that in an ideal situation you should always use an n-port calibration to measure an n-port device, but if that is not possible, then using the calpod load states as a termination for the unused ports shouldn't make your measurements any worst and it may actually be a little better than not doing anything.{quote}

We find that the load state gives us much worse results than the thru state. (In the thru state the DUT sees the load inside the multiplexer.) We're just trying to find out if this is normal or if we're doing something wrong.

Thanks,
-Bill

> {quote：title = WDrago写道：} {quote}> {quote：title = daras写道：}故事的寓意是，在理想的情况下，你应该总是使用n端口校准来测量n端口
设备，但如果这是不可能的，那么使用calpod负载状态作为未使用端口的终端不应该使你的测量结果最差，它实际上可能比没有做任何事情好一些。{quote} >>我们发现
负载状态给我们带来比通过状态更糟糕的结果。
（在直通状态下，DUT看到多路复用器内部的负载。）我们只是试图找出这是正常的还是我们做错了什么。
>>谢谢，> - 从您原来的帖子中，我得到的印象是您将所有未使用的端口的calpods置于加载状态。
所以，如果您的DUT有4个端口，并且您有一个多路复用开关矩阵，可将您的2端口VNA扩展为4端口，并且您使用2端口校准测量DUT端口1的回波损耗，那么您是
将其他3个calpods置于负载状态？
如果你正在使用2端口校正，那么你必须留下仅在你的校正路径中的2个calpods（在直通状态下）。
如果需要，可以将其他2个置于加载状态。
让其他2端口终止或不终止的影响将取决于DUT内所有端口之间的耦合程度。
如果我误解了您的申请，请提供您的设置的方框图。



     以下为原文

  > {quote:title=WDrago wrote:}{quote}
> {quote:title=daras wrote:}So the moral of the story is that in an ideal situation you should always use an n-port calibration to measure an n-port device, but if that is not possible, then using the calpod load states as a termination for the unused ports shouldn't make your measurements any worst and it may actually be a little better than not doing anything.{quote}
> 
> We find that the load state gives us much worse results than the thru state. (In the thru state the DUT sees the load inside the multiplexer.) We're just trying to find out if this is normal or if we're doing something wrong.
> 
> Thanks,
> -Bill

from your original post, I got the impression that you are putting all the unused ports' calpods to the load state.  so if your DUT has 4 ports, and you have a multiplexing switch matrix that extends your 2-port VNA into a 4 port, and you are measuring the return loss on port 1 of your DUT using a 2-port calibration, are you then putting the 3 other calpods into the load state?  if you are using a 2-port correction then you have to leave the 2 calpods that are in the path of your correction alone (in the thru state).  you can put the other 2 in the load state if you want.  the impact of having the other 2-ports terminated or not would depend on how much coupling there is between all the ports inside your DUT.    If I am misunderstanding your application, please include a block diagram of your setup.