Capacitance extraction

Discussion in 'Wireless & RF Design' started by Bero, Jan 18, 2015.

  1. Bero

    Thread Starter New Member

    Dec 17, 2014
    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 ?
  2. MikeML

    AAC Fanatic!

    Oct 2, 2009
    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...
  3. t_n_k

    AAC Fanatic!

    Mar 6, 2009
    Don't see how a passive component can have a negative resistance component in the complex impedance.
  4. Bero

    Thread Starter New Member

    Dec 17, 2014
    Yes, but I need some initial values for that. How to get them ?
  5. harry85

    New Member

    Jan 21, 2015
    RLC model surely help you very well