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

Question asked by drkirkby on Aug 27, 2012
Latest reply on Aug 29, 2012 by drkirkby
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

nor in Mathematica

but I've been told something suitable exists in the GNU scientific library.

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