Use phased.FreeSpace or phased.WidebandFreeSpace when radar waveform is FMCW 77GHz with 4GHz bandwidth?

Hi,

I use 'backscatterPedestrian' and 'backscatterBicyclist' to simulate radar echo from a FMCW radar, if fc = 77GHz and bw = 4GHz, which freespace propagation function should be used, 'phased.FreeSpace' or 'phased.WidebandFreeSpace'? And what if bw=1GHz or 2GHz? Thanks in advance!