This is a WiFi antenna upgrade I built following the instructions in an article of the german computer magazine c't. It's a yagi antenna designed for the 2.4 GHz frequency range and gives the wireless connection a directional characteristic and therefore a gain in the main direction. This model is intented to be built with “litter parts”. The construction is quite easy (it took me only 20 minutes) and the result is impressive!
The dimensions for the distances and the length of the beams have been calculated by the german ham Bodo Woyde, DL7AFB. His original documentation can be found here (german).