I personally used a myriad
of RF design tools such as ADS, Microwave Office
For linear simulation, all
of these tools are the same as the solve linear
equations and therefore provide identical results.
For non-linear simulations there might be some difference
because different tools use different algorithms
to converge to final solutions.
For EM (Electro-Magnetic)
simulations, there is a hugh difference between
different tools because they use completely different
methods to solve, some of them are 2.5D, some of
them are 3D. Here the cost of the software plays
a major tool on the amount of memory provided, the
solving time etc.
I used OrCAD, Dx
Designer (Viewlogic), nowadays I am using some low-cost
tools and eventually will use Altium Designer. The
cost of the software also plays here a major role.
I always start a new design with a paper and
pencil to gather my thoughts and to see how I fit
the design to meet the requirements, and then I
am heading to do some simulations (depending on
the complexity of the design).
In any case,
and this any engineer in any field will tell you,
that once a design is completed, it will be tested
- no matter how good a simulation tool is, there
is still no alternative to test and verification.