how find S12 or S21 in a 2 port structure with HFSS?

Hi.

I need to find the combined reflection coefficient of a two port structure in hfss.Does somebody has a clue on it?
in fact my structure (a copper tube) is fed simultaneously by two lamped ports.I used from coaxial cable for feeding After simulating it somebody can have s11,s22,s21,s12 but these parameters refer to each port when the other is matched.
This is not my purpose.
I want to find S12 and S21,when both ports are working simultaneously.
how can I do it?
thanks
ghasem

there is not any help?

Your question is not too clear. First it sounds like you have a 3-port network, and depending on which port you
consider the input and output you might want S23 or S31....

You should show a diagram or the layout of your design and you might get a response.
You can try to graph your simulation output.

yes,I have to attach a shematic.
this picture is my structure.

I have two signal (signal 1 with center frequency = 500 MHz & signal 2 with center frequency = 100 MHz)
how implement this structure in HFSS and find s12 and s21?