wifi problems

I am having problems with my wifi signal on iphone 5, It only picks up wifi signal when you are in the same room as the router (have tried various different routers and locations, all the same problem). Signal is lost when move about 5 metres away from router. Problem is definetly not router.

I have been to an apple shop, they gave me a brand new iphone 5. Reset to factory settings and updated to version 6.0.2 and still have the exact same problem.

Itunes is up to date.

HELP!