I've upgraded my laptop's Wireless Card to one that features 3 antenna ports (intel ultimate N 6300 minipcie).
Unfortunately my laptop only has two antenna connectors, which I've connected on the edges of the card, leaving the "middle antenna" vacant. The card seems to perform reasonably well nonetheless.
I'm wondering what the purpose of the middle antenna is, or perhaps the purpose of all 3 antennas - and which connector is best left out when one has only a limited number of antennas available.