Antena Yagi GSM 3G/HSDPA

Building a Yagi for 3G i.e. 2 GHz is a very very difficult task, you have to be extremely careful, and still have problems with tuning. Radio Hams have been successful in designing Yagis for 1296 MHz but even here it is difficult. Things like thickness of elements and how the boom affects the over-all of the antenna makes it hard. You will have to measure the ready made antenna and then adjust for gain and F/B.
You will save a lot of trouble and build a small mesh type parabolic reflector!

But there are brave people acctually building Yagis try google :design your own yagi 3G GSM HSDPA