S-parameter of spiral inductor on Smith Chart

when I simulate spiral inductor , I see the S-parameter result.
I can realize S11 , but I can't realize S21.
Why is S21 is in lower plane ?
How to explain S21 of spiral inductor ?

thanks a lot

Hi myem !

Smith Chart is a polar diagram for R.L. (S11, S22, ...)
You, can't plot S21 (transmission\insertion\coupling coefficient) in this chart.

The S21 in dB scale of your spiral inductor should be near -1dB.

see next link:
http://eesof.tm.agilent.com/docs/rfd...orSpirals.html

I.C.