Impulse response h(t) of UWB antenna from S11 parameter

Hi,
I simulated a UWB vivaldi antenna in HFSS. I would export S11 as .csv file from HFSS and import it in MATLAB.
The purpose is to find out impulse response h(t) of UWB antenna.

After importing .csv file of s11 from HFSS, what I need to perform to get impulse response h(t) of that antenna?
Thanks

S11 can only give reflected pulse shape (by applying fourier transform), For transmitted/received pulse response you need S21 measurement.

Thank you.
I have already placed two identical vivaldi in HFSS with a separation of far field distance and simulated the S21.
Given that I have exported this S21.csv file to MATLAB, what would be next step to get h(t) from S21.csv file? Do I take Fourier transform or inverse FT?

Inverse fourier