how to test differential inductor with unbalanced 2-port VNA

hi, I am going to test some on-chip differential inductors with an unbalanced 2-port VNA. The center-taps of the inductors are physically grounded. The problem is: if I assign stimulus on one terminal of the inductor, the section between the center-tap and the other terminal will be disabled(shorted). I have read some articles about mixed-mode S parameter, and I really doubt the possibility of mathematically tranfer this unbalanced result into a balanced one, because the mutual coupling between the two halves of the coil is totally missing. Could anyone enlighten me? I am really confused.

you can correctly get the inductance and Q
with below equation
L=image(Z11+Z22-Z12-Z21)/(2*pi*freq)
Q=image(Z11+Z22-Z12-Z21)/real(Z11+Z22-Z12-Z21)
if it's symmetrical, you can reduce them,enjoy!

I have got some idea about the problem. thx anyway!