You'll find information on this kind of antenna in many publications.
It's commonly called a "discone".

Roy Lewallen, W7EL

Maarten wrote:
Tnx fer ur ideas OM's, I will surely check the books out.
I might choose a monopole conical antenna for broadband vertical
omnidirectional radiation (if I discover building plans somewhere) (if
you do'n know what a monopole conical antenna is, check out
http://www.antenna.be/vm.html )
I will keep researching this subject, so as before, all ideas and
suggestions are more than welcome.

73