If you mean that the iPad disconnects from WiFi when in off/sleep mode, that's a feature Apple built in (to save battery). The good news is, that since it's a battery-saving feature, WiFi does not get switched off when the iPad is plugged in to a main power source (e.g. a wall outlet).
So, the only way to stop the WiFi from disconnecting is to have your iPad charging.
Hope this clarifies.
Marilyn