I started RF antenna modelling using
various versions of NEC, like EZNEC. You can play
around with simple wire structures and see what
happens as you change sizes, spacings and frequency.
There are many free sources of this software. It
grew out of a DOS version to which a number of people
added Windows front-ends.
For circuit simulation,
again free I believe, there is APPCAD, which can
be downloaded from
If you can get hold
of a copy of Mathcad, then the following site has
a number of Mathcad routines for RF design, including
Hope that helps.