AnsweredAssumed Answered

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

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  

Outcomes