This sector antenna was made from a piece of thick copper wire formed into a "bowtie" shape (the biquad - with sides 32 millimetres) and soldered to a round N-type connector. The N connector was then screwed into a steel disc about the size of a CD.
http://flakey.info/antenna/biquad/
the gain of the double biquad is approx 2dBi higher than that of the biquad, which is a significant improvement (as 3dBi is a doubling of signal)
http://martybugs.net/wireless/biquad/double.cgi
easy to build, and provides a reliable 11dBi gain, with a fairly wide beamwidth.
http://martybugs.net/wireless/biquad/
a dish with 27-31 dBi of gain and negligable sidelobe radiation (<40dB). The beamwidth is about 4 degrees.
http://trevormarshall.com/biquad.htm