HFSS S21 greater than 1?

Hello,

I have a 2 port model in HFSS with 50 ohms lumped ports. Basically there are 2 coils coupled together at a frequency near 10 MHz. I got an S21 value of slightly greater than 1 at the resonant frequency. Does anybody know why this happened?

HFSS uses the Finite Element Method in the Frequency Domain that is a numerical method. using the numerical methods need to mesh the objects nice and having knowledge about the kernel of the method. So if you have S21 greater then 1 means that you can not execute the HFSS good. you should change the setting and run it again to correct the file.