Uncle,
Try 'rational' for the interpolation method in the 'n2port' instance.
I had to import from an other tool like you did and it works for me
in ac analysis.
However, for Transient analysis, 'rational' does not work and i read
somewhere (don't remember where) that 'spline' should be used.
Vara

Thanks, I tried using 'rational' but it did not work. Basically what I have is a balun where in the primary one port is connected to VDD and the other to the signal and the secondary is a differential output. So when I run transient or DC analysis I get garbage since there are no DC voltage or current flowing from VDD to the main circuit.

Bit late in replying, but probably I would suggest using spline or linear as the interpolation method. I'd also recommend setting "Use smooth data windowing" to "yes" - this is nearly always the right thing to do; failure to do this often leads to an error in the DC value (but is more accurate if you have signals close to the maximum frequency in the s-parameter data).

There is an application note on sourcelink (search for "nport application note") which covers the parameters well.

Regards,

Andrew.