Sorry if this belongs in another section.

Small and high gain are probably exclusive.
I would settle for just directional.

I am working on a project that could do with a tight 2.4ghz beam. :)

Found these, 30,33dbi
http://www.zdacomm.com/2-4-ghz-gird-parabolic-dish-antenna-high-gain-seires.html
http://www.radiolabs.com/products/antennas/2.4gig/stage6.php

So in theory how tight could a beam be made?
1 Wavelength?

Is there another way to form the beam, say fire it down a tube?
Wave propergation is not my strong point.

Any help appreciated