Mesh frequency & density

Hello,

I want to know if mesh frequency and density can affect a simulation results(S-parameters,Radiation,Gain,...) for instance in HFSS and as an example let's say a patch antenna?

thanks.

yes, it can up to a certain point.
the denser the mesh, the more accurate it is, and the more time it takes.
You can play with the density until you do not see any appreciable change in results.