(I assume "a" in the diagram you linked to is the wire radius or
diameter, though it probably is not critical.)

Yes, it appears that it would be best if the feed is balanced. A
balun to transform from an unbalanced feed to a balanced one is a good
idea for this antenna. You can put the balun at the antenna, or some
distance away and feed from the balun to the antenna with balanced
line, if the line is arranged symmetrically with respect to the
antenna. It would also be good to know the approximate feedpoint
impedance of the antenna. An eznec (or similar) model of the antenna
should give you an idea about the feedpoint impedance. If you use
coaxial feedline to the balun, which connects in turn directly to the
antenna, and if you dress the feedline so it runs away from the
antenna perpendicular to the wire where the feed point is, a single
balun is likely enough, but if the feedline runs away from the antenna
at an angle, it may be advisable to also use a choke-type balun
perhaps 1/4 wavelength from the feedpoint. On the other hand, I would
not expect enough gain from this antenna that it would matter a lot,
and you may do fine not using a balun at all and just letting the
feedline radiate a little.

Cheers,
Tom

"emma" wrote in message ...
In the picture below appears the geometry of the Hentenna.
No constructional details are given.

http://antennas.ee.duth.gr/recradioa...ntennaGeometry
/Hentenna%20Geometry.htm

However I can use a balun to connect the coaxial line with the connector.
Because of the skin effect there is current in the interior and the exterior
of the conductor.
Firstly this current is only superficial.A part of it ends into one of two
wires.
As result we connect an unbalanced system(coaxial line) with a balanced
one(conductor).
In order to avoid this we use a balun which is a geometry transformer.

I ask for more comments.

Emma