I install grid antennas for all the Clear WiMax installations that are in fringe areas. Several users operate at over 5 miles from the tower.
Most of the time I use the 2.4 GHz 24 dBi Die Cast Mini-Reflector Grid Antenna from l-com. It has a very broad frequency range, the gain does drop off from the 24dbi to around 20 when used on the higher WiMax band.
»www.l-com.com/wireless-antenna-2 ··· onnector
In the past I have found on ebay some 24 dbi grid antennas that were used, in very good condition and they were cut for use with WiMax.
I recommend using Google Earth to map an elevation profile from your location to the Clear tower. That way you have a better idea of how high you need to elevate the antenna. Close in trees will be a problem.
Look around Jim's site for details about installing the antenna. »evdotips.blogspot.com/2008/10/pa ··· nna.html
Try to keep the antenna transmission cable as short as possible to reduce signal loss. Place the modem/router just inside the house at the antenna cable entrance point. I use LMR-400 cable.