I purchased a single RT-AC66U wireless router to replace an old Linksys router that I had a wireless extender on to give me coverage over my entire house.
The old linksys router was fine but I would only get 1 bar of coverage on the other side of my house, the range extender I used (which was essentially just another linksys router with the same SSID configuration and connected into the main router) kept crashing and I'd have to restart it all the time.
Anyway, teh RT-AC66U had much better range than my old linksys but not quite enough power to get full signal on the opposite side of my house.
So I purchased this WL-ANT-157 Antenna and simply hooking it up to the middle port of the RT-AC66U router increased my coverage to full signal throughout my house.
Installation could not be simpler, unhook the original antena from your router (simply by unscrewing it), then screwing in this new antenna into the same spot.
It says it's a directional antenna so I pointed it in the general direction where I needed the better coverage. Could not be easier.