Tere are some interesting result of testing panel antenna for wifi band on Russian site : http://www.lan23.ru/forum/showthread.php?t=1009
Antenna is tested when the pcb print is looking toward to a reflector and back.
You get lower SWR when the pint is looking to a reflector - pictures shows all :
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.
http://members.cox.net/nx7u/ao40/backfire/backfire.htm
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 :
Very Cheap Dipole feeders - they are easy to be build and you do not need a lot or expensive materials. Everything here can be made from wire or scrap /I watch too much scarpwars on Discovery channel /
I found some very interesting looking feeders for dishes - VERY cheap to make, first is made only from feeder line or simple coax.
http://patraswireless.net/antennas.html
“A simple dipole feed. Good solution to illuminate parabolic constructions (solid, grid etc.) Heliax holds the dipole, as well as feeds the N-type female connector to the back. Tests shown 4 dBi (against Lucent 24 dBi parabolic grid). “
Second is Russian of course http://www.hub.ru/forum/index.php?showtopic=16285
Name of the file is interesting too D_Linc3_008.jpg
Interesting materials - onli several pieces of pcb board are used - very good.
From the same forum are these too -
Last pic is from http://martybugs.net/wireless/conifermods2.cgi
And for the end howto make wire reflector or DIY Parabolic Grid Reflector
Info is from this : http://www.zero13wireless.net/foro/showthread.php?t=248
19dbi gird blueprint :
For me is easy to buy small offset dish - 80cm is around 10 to 15 Euros here.
Horizontal Polarized Omnis are mystery for me . Anyone was seen open vertical polarized omni for wifi. Whit horizontal ones there is another story. Except slotted waveguides /these works great/ , but they are really big things.
Here is one idea for horizontal omni or “double helix antenna” :
http://hft.uni-duisburg-essen.de/amateurfunk/amateurfunk_en.shtml
Mast is used for reflector for for this one. Ant in the internet there is a lot of designs for spiral antenna. Difference here is that is used dual spirals. Coaxial line is hidden inside of the mast, and its look like that feeding point is on the bottom of the antenna.
One more link - there was calculator for this antenna on that treat : http://wireless.com.pt/forum/index.php?topic=15786.0 but now I cant find it.
Thanks to the rt_rex You can find calculator on this site : Omni Helix XLS
I hope that soon we can see some results and tests of this antenna.