You do not necessarily need an Ethernet cable to use the TL-WA850RE as a WiFi range extender. The device can connect to your router wirelessly, using its Wi-Fi capabilities to extend the signal to other areas.

However, if you want to connect the TL-WA850RE directly to your router via an Ethernet cable to avoid any signal loss and ensure full speed, you can do so. The TL-WA850RE has a single 10/100Mbps RJ45 Ethernet port that allows it to function as a wireless adapter or to connect wired devices.