The PXI-5660 and associated software (Spectral Measurements Toolkit, Modulation Toolkit) are very tightly integrated with LabVIEW. I might be unclear as to your situation, but I will look at this from two perspectives:
Hardware perspective:
If you are testing a 2.4 GHz antenna, if you wanted a digitizer to simply digitize the output of the antenna, it would have to run at a sampling rate of at least 4.8 GSamples/sec due to the Nyquist Sampling Theorem. Other options include placing an RF downconverter in front of a digitizer. The downconverter then shifts the signal of interest to a lower frequency, which also lowers the Nyquist ctiterion, allowing lower sampling rates to be used.
None of NI's DAQ boards can sample fast enough to captu
re RF signals, unless there is some form of signal conditioning on the front end, like a downconverter. The PXI-5660 RF Signal Analyzer uses this approach.
Software perspective:
Once the data is acquired, it can easily be analyzed with LabVIEW analysis VIs and with the new Modulation and Spectral Measurements Toolkits (both in LabVIEW). Regardless of how you acquire the data, LabVIEW can analyze it.