First - I never made any helix antennas, nor spirals or anything similar. Consider this as warning BUT in the HAM world spiral feeders used in dishes is something very often used.
Very simple - small spiral and reflector in front of the dish.
It looks like that in the spirals there are several modes endfire and the normal-mode. This modes are explained on the side, but more reading is needed. Also there is right and left hand rule in these antennas.
On the page is a NEC code witch may be useful to simulate this antenna.
Dimensions on the pictures are given for 2401MHz but the peak for this is around 2.3ghz so for tests whit wifi we must change dimensions a little.
If anyone have the references as PDF - do not bother to send them to me
more pics :