# Thread: Can I determine electrical delay, C0, C1 and C2 of a home-made cal kit?

Replies: 6 - Pages: 1 - Aug 29, 2012 6:37 AM Last Post By: drkirkby Threads: [ | Next ]
 Posts: 282 Registered: 06/18/08
Can I determine electrical delay, C0, C1 and C2 of a home-made cal kit?
Posted: Aug 27, 2012 6:49 AM
 I have an 8720D 20 GHz VNA and an Agilent 85033E Mechanical Calibration Kit DC - 9GHz 3.5mm. Obviously the cal kit can't make best use of the VNA, but at this moment I can't afford the better 85052B 26.5 GHz kit. Is there any way I can calibrate the VNA with the official 9 GHZ kit, then find the parameters of the electrical delay (ps), C0, C1 and C2 of my homemade 3.5 mm open, so that I may use it for less critical measurements, perhaps upto 3 or 6 GHz. It's fairly easy to calculate the input impedance of a transmission line of length L, terminated in some arbitrary impedance Z. So I should be able to find an equation of the form. Z (frequency) = f (frequency, delay,C0, C1, C2) I could do similar with the short, and find the delay, L0, L1 and L2. Then I would have thought a non-linear fit of the measured values of Z on my open, over the range of say 0-6 GHz, would allow me to calculate values for the delay, C0, C1 and C2 for my home-made open, and the delay, L0, L1 and L2 for my short. Finding a suitable fitting routine does not seem easy. There does not appear to be one in the Sage open source maths program http://www.sagemath.org/ nor in Mathematica http://www.wolfram.com/mathematica/ but I've been told something suitable exists in the GNU scientific library. http://www.gnu.org/software/gsl/ Before wasting my time trying to do this, I'd appreciate if others feel this is practical or not. I've got several reasons for wanting to do this. A friend has a HP VNA, but only an Anritsu cal kit of unknown performance. I'd like to buy the 26.5 GHz 85052B, sell the 9 GHz 85033E, then use something cheap/homemade for non-critical measurements, to save wear on the expensive 85052B. Although I don't yet have an N cal kit, I do intend buying the very expensive 18 GHz 85054B N cal kit. Again, it would be good if I could have something cheap and cheerful to save wear on the expensive kit. Any thoughts? Dave Edited by: drkirkby on Aug 27, 2012 6:50 AM
 Posts: 259 Registered: 05/30/09
Re: Can I determine electrical delay, C0, C1 and C2 of a home-made cal kit?
Posted: Aug 27, 2012 1:16 PM   in response to: drkirkby
 Posts: 282 Registered: 06/18/08
Re: Can I determine electrical delay, C0, C1 and C2 of a home-made cal kit?
Posted: Aug 27, 2012 5:10 PM   in response to: drkirkby
 But if I did make a home-made cal kit, would the method I suggested by the best one to find the coefficients? Or would another approach be better? I noticed the foam inside the plastic containers for the centre conductor of the airline is my verification kit is breaking up. But I think it should clearn off the airline OK. It's interesting what you say about the load. I bought a very cheap APC-7 cal kit (HP 11866A), which I think is only rated to 2 GHz. But I was wondering how well that would work if the load was replaced with a better quality one. It would seem to me, that with APC-7, there's a lot less variables than with N. I don't have much use for APC-7, but the kit was cheap. It is not supported by my VNA anyway. Dave
 Posts: 2,379 Registered: 12/01/05
Re: Can I determine electrical delay, C0, C1 and C2 of a home-made cal kit?
Posted: Aug 27, 2012 5:35 PM   in response to: drkirkby
 7 mm is supported on 8720D, you just have to load the kit for it. Creating your own calibration standards is quite tricky; I recently went throught the process again (for a PCB kit to 6 GHz) and it took on the order of 2-3 days to sort everything out and verify results. If you want more details, I can point you to a reference.
 Posts: 282 Registered: 06/18/08
Re: Can I determine electrical delay, C0, C1 and C2 of a home-made cal kit?
Posted: Aug 28, 2012 7:53 AM   in response to: Dr_joel