On http://wireless.com.pt/forum/index.php?PHPSESSID=3a383f0ff0f782f5a00fea2c1e20e5d9&topic=15658.0 You can find interesting antenna projct cardboard slotted waveguide.
Aluminium foil and cardboard is used to build slotted waveguide wifi antenna.
Here some pictures :
Last picture is 11Ghz and 2.4Ghz versions compared.
Waveguide is tested and the resuts are very good - more than 14dbi are reached!
This is a good way to fast build and test antennas, also quick modifications are possable.
The bad thing is that You can not solder aluminium - which for this antenna is not a problem.
The author of this post call this “40cents antenna” and he has several different types of antennas builded and tested.
You can find the links on the http://wireless.com.pt forums.