using HFSS at low frequency, help needed

When using HFSS to calculate the characteristic impedance of CPW,
at low frequency, such as 1MHz, it will get give some ridiculous results,
anyone has such experience? but at higher frequency, 100Mhz, everything is fine, I cant understand that is why.

HFSS only works for high frequency. Use the RF mode of Momentum.

hmm... thanks for you reply, I know HFSS works well at high frequency,
but you can check the setup of frequency sweep, there is an option about the interpolation DC, it should can handle low frequency.

You could surely try that. It's not accurate, though. It only calculates at DC (0 freq) and lowest high freq it can get, then interpolate it.

thank you~ definitely I have tried that, S-parameter seemed ok, but the characteristic impedance.... so the lowest frequency is 100MHz or 10 MHz?