Anyone who has made this measurement knows you need to drive your device (one with non-linear behavior, thus the distortion) with two signal sources (slightly seperate frequencies) and test equipment to measure the output signals (the two input signals plus the generated intermod tones), usually a spectrum analyzer.
Agilent's network-analyzer-based approach does not require any external computer or hardware beyond the PNA-X network analyzer. Instead, dual internal sources and a built-in signal combiner provide fast swept-IMD measurements, according to the company - approximately 100 times faster than spectrum-analyzer based solutions. This approach results in higher throughput in manufacturing and faster time-to-market for R&D engineers. An internal calibration routine ensures accurate answers, yielding better data for R&D designers as well as tighter specifications for manufacturing engineers. Apparently the applicxation includes a spectrum mode which enables troubleshooting without the need for a seperate spectrum analyzer.
Joel Dunsmore from Agilent wrote about the new capabilities by today's network analyzer to do more than just S-parameters in his March "Expert Advice" column on the Microwave Journal web site. It may be a good time for those of you who missed it, to go back and give it a read.