Sorry that I warm up this old topic.
Well, this matter has gained new importance in conjunction with the actual 802.11ac Wifi standard. And to make it even more complex, there exist meanwhile also some Wifi / Bluetooth combo cards with up to four antenna connectors.
Just to be clear, I absolutely understand, a Wifi card with three antenna connectors will work with just two aerials. My question is how good / reliable this will work?
For example, with only two antennas, a three stream 3x3 802.11ac Wifi card like Broadcom’s BCM4360 will not reach it’s 1.3 Gbps maximum data rate. Most likely you will get only 867 Mbps, one third less, because one antenna (one „stream“) is missing. Even more difficult is the situation with the mentioned combo cards with up to four antenna connectors. Such cards would work absolutely inefficient with only two aerials. In the worst case, the Bluetooth part will be completely unusable.
Therefore one of the most ideal 802.11ac upgrade solutions seems currently Intels 7265 Mini-PCIe card range. These models only needs two antennas (2x2) and offers 867 Mbps maximum data rate. Interestingly, no additional bluetooth aerial is needed on these Intel cards. The previous Intel 7260 range may be also an option, - it seems that their initial hardware flaws are fixed with the latest driver releases.
Well, regarding any three stream 3x3 802.11ac solution, there is no way around, you have to add an additional antenna. On most laptop devices that may be near impossible but at some All-in-One computers this should be less tricky.
For instance, my older Apple iMac computer has 2x2 configuration 802.11n Wifi (2 antennas) and a separate Bluetooth module (1 antenna). My plan is to replace these two parts with one Apple BCM94360CD 802.11ac Wifi / Bluetooth combo card. The new one has four antenna connectors, so one aerial is missing in my case. I can decide between full 1.3 Gbps performance in 3x3 configuration but no working Bluetooth, - or 867 Mbps in 2x2 mode including working Bluetooth. As mentioned above, the best option is to add an additional fourth antenna, then I will have full 1.3 Gbps Wifi performance and working Bluetooth 4.0.
Finally, the last crucial point is the correct attachment of all these aerials. The four connectors on the new card are different labeled. They are described with A2, A3, A1 and A0 (sometimes also J2. J3, J1 and J0). Currently I have absolutely no plan regarding the right connection order. It seems only sure that one of these connectors is Bluetooth exclusive…