Sure, check:
http://forum.mikrotik.com/t/wap-coverage-picture-included/179859/1
http://forum.mikrotik.com/t/netmetal-ax-antenna/182772/1
While you can use straight antennas (NOT using the cover) the idea is to have two short length of cables connecting the antennas (the cables run in the two gaps on the side of the cover).