Below is a summary that will help you choose between different HFSS sweeps.
Remeber that no matter which sweep you choose you should get the same results.
1) Fast Sweep
The fast sweep finds the "poles and zeros" of the problem to calculate S-parameters. Fast sweep should be your "default" as long as Fmax/Fmin < 4 (rule of thumb). Fields are available on all frequencies.
2) Interpolating Sweeps
This sweep is ussually used when a DC solution is needed or a very broadband sweep Fmax/Fmin > 4. HFSS chooses which frequency points are "ideal" for interplating the S-parameters. The downside is that it does not produce fields (just S/Y/Z parameters). If you require a field solution in a specific frequency use an interpolating sweep together with a single frequency discrete sweep (use the same Setup - to reuse the mesh from the interpolating sweep).
BTW - together with the new DC thickness option, HFSSv10 is now used to produce highly accurate S-parameters from DC through MHz up to tens of GHz (and beyond). In the past users were required to solve inside metal which increased the simulation time.
When simulating very broadband S-parameters, one may want to use two interpolating sweeps. The first one up to the third harmonic with a high interpolation accuracy and the second sweep complementing to the fifth harmonic with reduced interpolation accuracy. HFSS interpolation in high frequencies is always superior to that of a circuit simulator.
Discrete sweeps are rarely used. Some engineers that require only 5 or 10 frequency points claim that discrete sweep may be faster.
Discrete is the only sweep where the simulation time is proportional to the number of frequency points specified.
I only use it to calculate fileds after doing an interpolating sweep.
Those of you that have a dual-processor machine with the HFSS multiprocessor license will see a significant speed increase (in all sweep types).
Fast Simulations everybody,