[bsamuels]

theres a two reasons your router probably has 3 antennas:

-beamforming

-split 2.4ghz/5ghz/5ghz-wave2 antennas

if your router is using those three antennas for beamforming, you might trigger some strange behavior if you yagi a single one of them. if run into issues and can turn beamforming off, you should be able to yagi a single one no problem.

if your router pumps each antenna into a separate radio, then you can reliably pump a single radio into that corner of your house w/ a yagi. however, you won't have seamless roaming between the 2.4ghz and 5ghz networks when you move into and out of that corner of your home.

i recommend getting a mesh network, they're the bees knees and are a huge step above the traditional access point + range extenders model