If you use a router as an extender, it will communicate on the same channel as the main router. An extender such as RE220 can be set up to work on the 2.4 GHz for one direction and the 5 GHz for the other direction of traffic. That limits your speed to the slower of the two bands. An Ethernet cable can be used in some cases and as I understand in some setups, a tri-band router can be used. A Mesh system does it all better.