Barry don't confuse the helix antenna that I originally mentioned and that Jerry is now talking about with a helical antennas.
'Helical' antennas are by and large either top, centre or base loaded vertical antennas used for mobile (typically) HF/vhf/uhf coms.
All this might be confusing, but unfortunately the Helix antenna is so named because it is formed as a helix. The helical (whip) is so named because it can sometimes be simply a helically wound copper conductor formed/stretched over a fiberglass rod or similar. It will be vertically polarized with a main radiation lobe being closer to vertical, the more loading it has(the physically shorter it is compared to the wavelength it is tuned for).
This is why a 1/4wave helical whip will have less than unity gain. The true Helix antenna will as Jerry said have circular/elliptical polarization, but its direction of action is parallel to the axis of the helix. It has an attractively high gain over a standard dipole.
Just remember that even though an antenna might be called a 'helical', when looking for high gain and directivity, a helix is meant, not a mobile whip.
cheers,
Doug