My iPad Air (1) started dropping the Wifi connection at random times just after the major upgrade to iOS 11.0.
Since then I have taken all the updates (6 I think now!) and am now running 11.1.2. I have experienced the same problem with every update - i.e There has been no difference with the dropped connections.
I've been through the recommended steps of Renew Lease, Forget Network, and Reset Networks - None had any positive effect. I've 2 Android phones and a laptop (Windows) which have no problems using the same wi-fi connection.
Apple have told me that it's likely to be a hardware fault with the Bluetooth module - but I've been testing the BT connecting to a variety of devices with no problems at all.
That, coupled with the rather big co-incidence of this problem only starting after going from 10.3.3 to 11.0, just doesn't make sense to me - and haven't found any results from searches of similar forums which I’ve done.