Marion: Microwave ovens operate on the exact same "frequency band" as does wifi. Goldstar Microwaves used to be very bad causes of wifi interference newer ones seem better. IF your oven is blanking out your wifi you may have a bad oven seal!! That is a dangerous situation which means you should have your oven checked for leaks! RF leaks can cause many health issues particularly on microwave bands! The other issue is the circuit that drives the magnetron in the oven. If the system has a power supply or tube issue it can be very dangerous to humans, animals, etc. Most good systems will not cause that much interference with wifi, if they do they need to be checked.
Added after best answer was selected:
If it is only your tablet that is affected, and other WiFi devices continue to work normally, then the problem may not be the microwave oven, but a compatibility issue between the tablet and your router. Sometimes changing the wireless channel that the router is using can solve this problem.
If multiple WiFi devices lose contact with the router, please get the microwave checked out. Keep away from the microwave while it is cooking, and be particularly careful with your eyes. If the oven is leaking microwave energy, then you can damage your cornea, which will require corrective surgery (cornea replacement). Cornea damage is more common than other problems caused by microwave ovens.
Personally I have never experienced any WiFi problems when our microwave is working. However, I have experienced problems with one or two specific devices not working properly on WiFi when other devices work properly. If the microwave proves not to be a serious source of interference, then installing a wireless access point and connecting the tablet to that as a separate WiFi network. The laptop I am using today does not work properly with my router, so I use a WiFi Range Extender that provides a separate WiFi source for my laptop. I don't need the extender for the range, but as a different signal source it fixed the problem.
I hope you get the problem resolved and that your oven is safe.
Microwaves happen to spit out 2.4 GHZ noise when in use, which interferes with WIFI. You will need to upgrade to 5 GHZ dual band n or ac or make sure you have dual band and it actually operates in both bands (some will only use the 2.4 GHZ if it detects a 2.4 GHZ device.)
you have a leaky microwave and you are never having children