I need one which can cover VLF (100KHz or lower) through low microwaves (1-2GHz).

Here's the gotcha: It must also sweep. Most sweep generators have a lower frequency cutoff of 10MHz, and most standard signal generators don't sweep.

An exception to this is the Rohde and Schwarz SMG/SMH series, and that's the way I'm currently leaning. Does anyone know of another synthesized model from HP, Anritsu or similar which offers these features?