用VNA测量大阻抗有多准确？

> {quote：title = Erumai写道：} {quote}>你好，>>当一个人使用VNA进行测量时，在RF频率上测量大阻抗（比如> 1 k欧姆）会有多准确？
对测量电缆与被测器件的杂散电容耦合有多敏感？
>>谢谢它归结为反射跟踪精度，而简短的回答是“不太准确”。
但算一算：1kohm是0.904反射（0.9 dB回波损耗）。
如果源匹配和方向性各自为-40 dB（0.01反射），那么rss误差将为0.014，测量值为0.918，或阻抗为1171.但是，如果你有，你可以自己想出来
读我的书;-)



     以下为原文

  > {quote:title=Erumai wrote:}{quote}
> Hello,
> 
> How accurate would measurement of large impedances (say > 1 k ohm) at RF frequencies would be, when one uses a VNA to do it? And how susceptible it is to the stray capacitance coupling of the measurement cables with the device under test?
> 
> thanks

It comes down to reflection tracking accuracy and the short answer is "not very accurate".  But do the math:

1kohm is 0.904 reflection (0.9 dB return loss).  If the source match and directivity are each -40 dB (0.01 reflection) then the rss error would be 0.014, and measure would be 0.918, or an impedance of 1171.  

But then, you could have figured that out for yourself, if you had read my book  ;-)

> {quote：title = Dr_joel写道：} {quote} >> {quote：title = Erumai写道：} {quote} >>你好，>>>>>测量大阻抗（比如> 1 k ohm）的准确度是多少
当使用VNA进行射频时，RF频率会是多少？
对测量电缆与被测器件的杂散电容耦合有多敏感？
>>>>>谢谢>>>归结为反射跟踪精度，简短回答“不太准确”。
但算一算：>> 1kohm是0.904反射（0.9 dB回波损耗）。
如果源匹配和方向性各自为-40 dB（0.01反射），那么rss误差将为0.014，测量值为0.918，或阻抗为1171. >>然后，你可以自己想出来，如果
你读过我的书了;-) Joel，你怎么看待高阻抗*串联*并进行S21测量而不是反射（S11）测量？
当然还有其他更适合这种的仪器，由Keysight出售，我认为主要（如果不是唯一的话）在日本开发，但不幸的是，日本的任何员工都很少阅读这些论坛。
戴夫



     以下为原文

  > {quote:title=Dr_joel wrote:}{quote}
> > {quote:title=Erumai wrote:}{quote}
> > Hello,
> > 
> > How accurate would measurement of large impedances (say > 1 k ohm) at RF frequencies would be, when one uses a VNA to do it? And how susceptible it is to the stray capacitance coupling of the measurement cables with the device under test?
> > 
> > thanks
> 
> It comes down to reflection tracking accuracy and the short answer is "not very accurate".  But do the math:
> 
> 1kohm is 0.904 reflection (0.9 dB return loss).  If the source match and directivity are each -40 dB (0.01 reflection) then the rss error would be 0.014, and measure would be 0.918, or an impedance of 1171.  
> 
>  But then, you could have figured that out for yourself, if you had read my book  ;-)

Joel, 

what do you think of putting the high impedance *in series* and making an S21 measurement, rather than a reflection (S11) measurement? 

There are of course other instruments more suited to this, that are sold by Keysight, and I think mainly (if not exclusively) developed in Japan, but unfortunately it is rare for any of the staff from Japan to read these forums. 

Dave