The ones I use are powerline adaptors. One of them plugs in near your home hub and you plug an etherner cable between the 2. You then put the other device in the area of your home that gets a poor signal. You can buy ones that are wired only, so that you plug an ethernet cable into the second one then either into your computer or another wireless router OR some home plugs come with a wireless device in them.
A quick google search of "powerline wireless" brings up a few options
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