U can buy certain repeaters that don't halve the bandwidth. They use the 2.4ghz and 5ghz concurrently, one for receiving from router the other for broadcasting to devices.
I have two of these and can vouch the wifi speed doesn't get as affected as by normal repeaters.
Netgear ac1200 (more expensive but amazing range) or linksys re6500 (cheaper but smaller range) both support.
Works fine with Asus routers too.