I'm building a temperature controller comprising a WiFi transceiver, AVR, and two relays, switching 240V (single phase -- I'm in Australia).
Because I'll have mains power in the box I want to use an earthed metal enclosure, but my 2.4GHz wifi board, a seeedstudio Wifi Bee has an on-board antenna made from a PCB trace.
I intend to cut a window in the metal enclosure and cover it with plastic.
How large does it need to be, and where should I put it in relation to the WiFi Bee's antenna trace?