This case it for an enhanced CC2531 zigbee sniffer which I use for my home automation.
The wireless is strong, but adding an external antenna still helps. The one in the picture may be a bit too much, but I had it at home and it works fine.
There is a similar case on the web which you can buy only and not available for free. So i decided to give back to the DIY open source community and design my own on, free to use for everyone.