I want to know that tool recommends me to make designs RF, either in a discreet or integrated way. I have multisim, and for what I have seen, it has the possibility to simulate circuits but built discreetly, sincerely i would not know if it allows to simulate circuits integrated RF. I wait comments.
You may wish to look for Qucs.
This is a freeware software tool with the same kind of interface as ADS, and also supports harmonic balance, optimization, etc.
I have tried many kinds of simulators but really found this to be the best available (and even at zero cost!).