Select the optimum frequency for your application. generally the higher frequency will have tighter mesh, so more accurate, but takes longer to simulate. pick the highest frequency you need to know accurately as your solution frequency.
The frequency is not so important. More important is the mesh density. You can run a simulation and increase the mesh density for a new simulation. S-paramters should be almost equal with both sims.
I'm less familiar with momentum specific settings, but in general, mesh density is indirectly set by the meshing frequency. higher frequency = shorter wavelength = tighter mesh to capture effects at frequency. If mesh density can be set independently from frequency then I agree with johnjoe.
I'm less familiar with momentum specific settings, but in general, mesh density is indirectly set by the meshing frequency. higher frequency = shorter wavelength = tighter mesh to capture effects at frequency. If mesh density can be set independently from frequency then I agree with johnjoe.
Sometimes the layout maybe quite complicated. In that case, I think whether the mesh density is dependent to freq or not, it is helpful to increase the number of density, by sacrificing simulation time.