[UWB] TX-RX voltage transform function

Dear all :
when we research uwb antennas , it always need to compute the TX-RX voltage transform function.

i will appreciate Dr. Hans Schantz, who is very famous in antenna field , he writes a mail to me that hfss can do the tx-rx function research. but he doesn't explain it in details .
and my question: how HFSS (or others software,if you know) do this work ?and how to set in the software ?
Does we simulate from one antenna's(Tx antenna) and use hfss's some functions to get the tx-rx antenna voltage transform function , OR , does we simulate through both Tx-Rx antennas to get the transform function ?
i will appreciate your help very much.
Thanks in advance .
woshifanka

ps : if you know ,please explain in some details , and a *.hfss as a example will be appreciated .

Hi, Fanka: On IE3D, we have a feature called Find Tx-Rx Transfer Function in the PatternView. You can find the transfer function. Not only that, you can put this transfer function in MDSPICE (Another simulator from Zeland) and find the time transient response received on the Rx antenna given a pre-defined stimulus. Regards.

Dear Jian :
yes , i find it in the manual, but till now i have not got the right time transient response received on the rx antenna , maybe i should read the mdspice manual again .
thank you very much.