Rick Karrer, 802.11n uses something called MIMO (Multiple Input Multiple Output), which basically means that it uses multiple transmitters and receivers, which enables simultaneous operation in both ends of a device.
Theoretical max data speed rate is 300Mbit (450Mbit utilizing 3 antennas).
With correct configuration, you should boost your possible max rate, by adding a second antenna. But remember: 150Mbit is the theoretical max, not the actual max (lower)