Below is a link to a comprehensive, 18-page paper delivered at the IEEE
Broadcast Symposium last September with an extensive mathematical analysis
and measured data from broadcast stations using CF antennas.

Some conclusions:

- A CF antenna is not quite as good in terms of gain and bandwidth as a
reference monopole of the same electrical height.
- CF antenna performance increases as height and/or top loading increases,
and for the same reasons it does so for a standard, short monopole.
- Given its performance, and the complexity of the installing/adjusting a CF
antenna, a short monopole over a good ground plane could be a better choice.

http://www.fi.uba.ar/materias/6654/d...CFAantenna.pdf

RF