Thanks to both for your replies.
Further to Jake: what I mean is that sometimes my iPad will lose its connection to the home WIFI. I say to my wife, "It's gone again!" But she may say, "Mine's still OK". This could refer to either her iPhone or her iPad because she uses both in the house. I must confess that I have not checked whether her iPhone and her iPad are both gone. Another time, she might lose her connection but my iPad is still OK. (I should add that although I have an iPhone, I very rarely have it on and never on in the house.)
It's a bit crude, but the only way thus far that we've been able to get the connection back is to switch off the device concerned. Usually, when we switch it on again a minute or so later, things will be OK. We live in a block of flats and I can see lots of different networks (neighbours) when I look via my MPB, which BTW, is only ever connected to Ethernet.
Such a WIFI disconnection might occur three or four times a day ... to her and/or to me.
We do use her iPhone as a hotspot for our two iPads and my MPB when we are away from home. (I've just looked at her iPhone and noticed that "personal hotspot" was "on" with "allow others to join" also selected. I've turned both "off" because we obviously don't need a hotspot when we are at home.)
Further to 'RadDave', we just have the one router/modem; this unit is provided by the company from which we get our telephone and internet. But I will try your suggestion about switching it off for a minute and then back on again.
Thanks again ...