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 ------------------------------------------------------------------ To unsubscribe from si-list: si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field or to administer your membership from a web page, go to: //www.freelists.org/webpage/si-list For help: si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field List technical documents are available at: http://www.si-list.net List archives are viewable at: //www.freelists.org/archives/si-list Old (prior to June 6, 2001) list archives are viewable at: http://www.qsl.net/wb6tpu ------------------------------------------------------------------ To unsubscribe from si-list: si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field or to administer your membership from a web page, go to: //www.freelists.org/webpage/si-list For help: si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field List technical documents are available at: http://www.si-list.net List archives are viewable at: //www.freelists.org/archives/si-list Old (prior to June 6, 2001) list archives are viewable at: http://www.qsl.net/wb6tpu