Goggling early in the morning some time give me some very interesting results π
This time is this thing – helix antenna whit reduced dimensions.
http://www.vtnews.vt.edu/news_print/index.php?relyear=2005&itemno=899
This thing have gain: 12dBi and dimensions only 165mm light and diameter of a dish 165mm
link : http://www.hitel.it/default3NSD.asp?tree=108&usr=-1&codlingua=1&grc=4&grl=16
Here You can find some patent info: http://www.patentmonkey.com/PM/patentid/5986621.aspx
On the net there is a lot of info I thing : http://scholar.lib.vt.edu/theses/available/etd-11242003-123529/unrestricted/Barts_etd_CH4.pdf
and also good article about traditional spirals http://scholar.lib.vt.edu/theses/available/etd-11242003-123529/unrestricted/Barts_etd_CH3.pdf
Here You have experimental build and testing of several of these antennas π
http://scholar.lib.vt.edu/theses/available/etd-11242003-123529/unrestricted/Barts_etd_CH7.pdf
Google is a great thing π