stimulating a parallel plate capacitor with voltage exciatation (HFSS)

I am stimulating a parallel plate capacitor(30X30X30 um^3). I have to apply a frequency sweep form 1HZ to 300 GHZ. I applied voltage as the exciataion and in the analysis I assigned the frequency sweep. I am assuming that HFSS would apply V=Vsin(wt) between the plates. Is that right? Is it reasonable to use voltage excitation for very low and very high frequencies? I have used lupmed port before but it did not give me the correct results. I need to keep the same source for high and low frequencies. Thanks for your comments. i really need it