Re: HFSS Vs CST
CST has multiple analysis modules available; you can choose time domain analysis or frequency domain analysis. HFSS is only frequency domain. Thus there may be some extra flexibility with CST, although I find that you need a little more expertise with CST and you need to be thouroughly familiar with EM analysis ( Maxwell's equations and boundary conditions at interfaces). I think HFSS is a little easier to use, but less flexible. If you search elektroda, you'll find a length discussion about these difference. If you are familiar with EM anaysis, then you may be able to make your own choice. Hope this tidbit helped.
regards,
MoonShine