iPad Mini WiFi disconects after screen is locked

Hi, I have an iPad Mini, the WIFI stops working after a few minutes when the screen is locked. I installed the new version 6.0.1 and still the same problem. I did also reset the network settings. But no luck.

I have 2 other iPads but with iOS 5 (my kids), an iPhone 4s and an iPod Touch, and they all have the WIFI icon when the screen is lock and get notifications (on battery mode)

With my brand new iPad Mini when I try to use SIRI on the lock screen, she will remind me that she is not avaliable. My WIFI is AWOL !!!

I´m thinking of getting a replacement seeing that Apple is like always ignoring the end user.