Hello

I have a doubt and I would appreciate if you could help me solving it please. I am using the VNA E5071C with a Picoprobe calibration substrate CS-5. What I would like to know is what Offset Z0 and what Arb. impedance exactly represent and the relationship between these two parameters and the System Z0. I would like to know this because in the VNA reference manual it says that "System Z0 should be changed to 1 ohm before calibration when using waveguide calibration kit and measuring waveguide devices" so I would like to know if it is necessary to do this with the CS-5.

I would also like to know something else. I am using GSG probes with a connection cable to the VNA. This cable has an impedance of aproximately 1 ohm. Is this impedance rigth? Shoudln't it be 50 ohm? By the way the DUT (device under test) I want to measure has a 50 ohm impedance.

Thank you for your help.

Cordial greetings

For the most part you can ignore these. Offset Z0 is the case that the offset open or short (offset by a short transmission line) has a transmission line whos impedance is not Z0. This allows it to be specified explicitly. It is almost never used except to fake up a value of inductance in the load (by setting the offset Z0 to a high value). Arb impedance allows the use of a non-50 ohm load as a reference impedance. In precision measurements, you might have a load that has 48 ohms resistance and a little inductance. You would use an arb Z load of R=48 ohms and an offset Z of 500 ohms with an offset delay equal to Lequiv/500. Details on page 559 of my book: http://www.wiley.com/WileyCDA/WileyTitle/productCd-1119979552.html

No, it probably doesn't. You are likely talking about the DC resistance. Most likely it is 50 ohms RF impedance. You can read about cable impedance in chapter 5, pg 274, of my book. The DC resistance is unrelated to the RF impedance.