UWB-Solution frequency-Radiation box

Hi
My antenna is an ultra wide band (3.1-10.6GHz) antenna.In hfss I gave solution frequency as 10.6GHz and drew radiation box corresponding to 10.6GHz. Is it correct? Please help....

The radiation box should be a quarter-wavelength long of the frequency of interest in the direction of the radiated field.

Specifically, the lowest frequency you're using -- so you want one quarter wavelength at 3.1 GHz.

i suggest using time domain calculation or MOM based solutions. because time is valuable in this situation!