[SI-LIST] Re: Question about diff-probes

  • From: "olaney@xxxxxxxx" <olaney@xxxxxxxx>
  • To: si-list@xxxxxxxxxxxxx
  • Date: Tue, 5 Jan 2010 05:39:22 GMT

Greetings, Zaiyi. The reason you can't find VNA diff probes is because they 
aren't needed.  The N1020A is just a mechanical positioner for whatever probe 
is clamped in it.  High impedance probes can be used on the input end of a VNA 
if they can drive 50 ohms but do not support reverse transmission.

The usual approach is to take a series of two port measurements and combine 
them mathematically.  A VNA with more ports than two makes the process easier, 
but it still uses a series of two port measurements.  Conversion to mixed mode 
parameters is explained at 
http://www.si-list.net/files/tech_files/Understandmm.pdf
The Agilent website has excellent information, including a nice collection of 
measurement examples.

Orin Laney


From: Zaiyi Liao <zaiyi.liao@xxxxxxxxxxxx>
To: "si-list@xxxxxxxxxxxxx" <si-list@xxxxxxxxxxxxx>
Subject: [SI-LIST] Question about diff-probes
Date: Tue, 5 Jan 2010 11:46:28 +0800

Hello experts:
        Now I want to test S-parameter of diff-channel on PCB.

       I find it's hard to find portable low-impedance(50ohm) diff-probe for 
VNA. As I know,there are some diff-probes up to 15Ghz (such as N1020A TDR 
probe) for TDR test. And there are lot of high-impedance diff-probes for 
eyepattern test up to 10Ghz. In chip test, there are many low-impedance 
probes(GSG,GSGSG,GSSG,etc)

      I want to know whether there is any portable(no need probe station) 
diff-probe for VNA?? Why it's hard to find low-impedance probe for PCB test? 
Another question is that what is the differences of S-parameter test by VNA and 
TDR.

   Thank you very much!

BR//Zaiyi Liao






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