Hey People

I have a very basic problem. The measurements on an interdigitated capacitor are made as 1-port measurements (one side connected to RF signal and other side of capacitor to ground), using VNA. I have four Z11 (or Zin) values of a interdigitated capacitor, for different frequencies.
They are:
0.045GHz Z= -2K -j*8K
10.033GHz Z = 0.76 -j*54
18.02GHz Z= 0.478 -j*12
40GHz Z= 60 + j*154

The model of the capacitor also has ESR and inductance as it is a transmission line for such high frequencies. Using these values, I have to find actual capacitance of the interdigitated capacitor. Can you please help me out with ideas ?

 

Postulate a lumped RLC model. Try different values of RLC to see if you can find a combo that matches your four measurement points. If you are lucky, and a simple RLC model works, you dont have to screw with transmission lines. OTOH, if the simple model is inadequate, then you can use this problem as your thesis...

 

Don't see how a passive component can have a negative resistance component in the complex impedance.

 

Postulate a lumped RLC model. Try different values of RLC to see if you can find a combo that matches your four measurement points. If you are lucky, and a simple RLC model works, you dont have to screw with transmission lines. OTOH, if the simple model is inadequate, then you can use this problem as your thesis...

Yes, but I need some initial values for that. How to get them ?

 

RLC model surely help you very well