The obvious starting point would be two sets of MA-ANT-20 (they are purchased in pairs), but that would deliver omni-directional coverage, in both 2.4 GHz and 5 GHz bands. You may be looking for something more tailored / derectional for your specific coverage needs.
Thank you very much, I am looking for omnidirectional antennas and I think that with the MA-ANT-20 they fulfill perfectly. Another question, are you telling me that I should only add 2 MA-ANT-20 antennas because they come in pairs? Or should I add 4 antennas to my quote?
@Jorge_Garcia : MA-ANT-20 are Dual Band Omni Antenna and comes in set of 2. so they can and should be used on all 4 ports of the MR76.
Note that when you order ANT-20 there are 2 physical dual-band antennas in the box, they come in pairs. So for any dual band AP like MR72/74/76 you would order 2 ANT-20 which would get you 2 pair, 4 physical antennas for the 4 physical ports.
Just to be clear; with MR76 you could use different antenna types, to provide different coverage areas for 2.4 GHz and 5 GHz, because each radio has its own pair of antenna posts. That is a fairly unusual requirement though - but I have seen it, occasionally with (say) wireless mesh; directional antenna on one radio (2 posts), in one band, for the backhaul, with (say) ANT-20s for local clients on the other radio. In that case the client connectivity would, essentially be in a single band only.
This differs markedly from MR86, where all 4 posts are connected to BOTH radios; for which the connected antennas must be dual-band and must cover the same area.