"steveeh131047" wrote in message
...
Also folded dipole tends to have broader b/w compared to dipole.

Due to the transformer effect of folding it.


Most of the bandwidth enhancement on a folded dipole comes from the
fact that it's a "fatter" radiator rather than because it's folded.
Section Bii) he

http://www.karinya.net/g3txq/folded_dipole/

Steve G3TXQ


Of course, the 'transformer effect' is unlikely to increase the bandwidth by
itself, and when the common type of half-wave-line balun (and 4:1 impedance
transformer) is used to connect the dipole to co-axial cable the resonant
nature of this additional half wavelength is likely to impair the bandwidth
to some extent (by introducing additional reactance at frequencies for which
its length isn't a true half wavelength).

Certainly the additional fatness of the folded-dipole structure must
contribute to improved bandwidth by reducing the slopes of the terminal
resistance and reactance, but the treatment given in the link provided
above - suggesting that the susceptance added at the drive point by the
'parasitic' parallel wire or rod, joined to the driven element at its ends,
has insignificant effect - is a rather broad generalisation which may not be
true for some geometries (i.e. length/thickness ratios of the wires/rods and
their spacing). Generally, it's dangerous to generalise!

There's quite a lot going on in a folded dipole. Some further insight (on
allied, but not the same, topic) is offered in
http://www.physics.princeton.edu/~mc...cutantenna.pdf.

Chris