MBA 2011 disconnects from home network (wi fi)

I have a MacBook air 2011 and for the first months I used it, it worked fine. Now it keeps disconnecting from my home network, sometimes the connection will last 10 minutes, sometimes a couple hours. I was recently out of the country and i am not sure if that had anything to do with my current problem.

I have tried resetting the DCHP lease, deleting and adding the network again, changing the IP address, but nothing fixes it. The only thing I have noticed, is that when the connection stops and I go to DIagnostics, it tells me that the IP failed, but if I click "Continue" it resets it and then tells me the connection is working fine.

what can i do?

thank you