Wi-fi range extender helps wi-fi router get the Wi-Fi signal to part of your house or apartment. Good wi-fi range extendera have ample range, speed, portability, and generous physical connections. 

The wi-fi range extender works by connecting to your existing Wi-Fi at a location that does get a good connection and then rebroadcasts its own signal(s), thus extending your Wi-Fi coverage beyond your router’s range

Before you decide on buying a wi-fi range extender, make sure you really need one. Change the location of your router. Put it in a more central location. Does it improve coverage? Or, maybe you need a new router. A new 802.11ac router will provide a better range and faster connections than your old router, especially if you have wireless-ac devices.

Another option before getting a wifi extender is to run an Ethernet cable directly from your router to your computer's Ethernet port or to a Wi-Fi access point or a router set up as one.

The best Wi-Fi extender: TP-Link AC1750 Wi-Fi Range Extender RE450 (best long-range performance)

The second best Wi-fo exxtender: Linksys AC1200 Max Wi-Fi Range Extender RE6500 (multiple Gigabit Ethernet ports, less flexible)