Re: UWB ANTENNA ISSUE
Seems to me you need to sweep the frequency, and at each frequency point measure angle[S21] Transmitted by your UWB antenna and received by a known standard antenna. Then you can calculate group delay by ΔΦ/ΔF.
The problem is that you are using free space radiation, and there are long cable lengths, a chamber, and the receiving antenna to calibrate out. All "calibrated" standard antennas that I have seen have amplitude, but no phase, calibration data.
I know there is a "3 antenna" method of calibrating amplitude of similar unknown antennas. Maybe (and I am just winging it here) a "3 antenna" calibration could be done for phase. Once you have calibrated out the phase shifts in your test setup, you substitute the UWB antenna in for the final test.