How to determine the frequency setup of UWB antenna in HFSS?

I am trying to simulate a UWB antenna bu using HFSS, but the problem is how to determin the frequency setup (for analysis). for example when i would to simulate the UWB to operate from 2GHz to 10 GHz, what is the desired frequency of analysis and how can i determiun it? . Can anyone help me!
Thanks for your help.

UWB & HFSS

Dear smnobo:
my friend and i discussed this problem , and in my opinion : the "solution frequency" is very important to UWB antenna , you know , if it is a frequency fixed MS antenna(has a center frequcny,when you design it ,for example) , the "solution frequency" is just fr, but regarding uwb antenna , it seems to if we set it higher will get a good result. my friend take a circle ring uwb antenna as a example , when he set the "solution frequency " at 12G , where the whole simulated band is 0-12G ,
the simulated result is close to the measured .
while i set the "solution frequency" at 7G , the result is bad . and we choose the "disctete solver".
hope this can help .
i will be glad if you can share some of your opinion.
rgz
kaka
please keep contact , my email is : fanqikai@163.com