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Calibration issues using an onboard open-shot-load standards

Question asked by GuiXZatS on Nov 13, 2015
Hi everybody,

I am trying to characterize a capacitor using a E5071C ENA.
To do the calibration, I am using OSL using standards built in the PCB where the capacitor to be characterized is placed.
Once I finish the calibration, when I connect the capacitor to be characterized, the plot on the smith chart goes slightly further than real(Z) = 0 circle in some range starting around 200 MHz . This means that the capacitor has gain, and this can not be the case.

  * VNA: E5071C
  * The frequency range is for 100 MHz to 5 GHz
  * The capacitor to be characterized is 6 pF 0402.
  * The load for the standard is 50 0.1 % 0402
  * Find attached gerber screenshot of the on-board standards 
  * Find attached Smith chart with markers showing the issue

  * What I am doing wrong?

Any advise will be really appreciated.