Radiation boundary in antenna

Dear Sir:

I know the radiation boundary in simulating antenna by HFSS9 should be quarter lamda away from the antenna.
But which frequency is this lamda according to, solution frequency, or some thing else?

Thanks a lot

Regards,

I think it is the frequency at which you want to compute the far-fields accurately. I usually use the lambda corresponding to the lowest frequency of the sweep.

-svarun