FreeLists / si-list / [SI-LIST] Curve fitting of center-tapped inductor

[H B <neoflash2008@xxxxxxxxx>]

Hi, folks: 
 
I come up with a strange thing when doing curve fitting for a differential 
center-tapped inductor. 
 
The original version of the inductor is a two-terminal differential inductor. I 
did curve fitting to find the equivalent circuit model. And the fitting seems 
good. 
 
The next step I added a center-tap and got a 3-port s-parameter from field 
solver. The problem is when I'm doing the curve fitting again. the mutual 
inductance in the circuit model was forced to zero by the fitting tool. The 
fitting seems OK but not as good as two-port one. The inductance and Q is ok 
but the s-parameter related with the third port are not well fitted. 
 
Any one ever experience same thing before? Any suggestions? 
 
Regards, 
Neoflash 
   
  I've attached the link where the equivalent circuit model could be seen.
  http://www.designers-guide.org/Forum/YaBB.pl?num=1205764700

       
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