Why can't iPad connection speed surpass 72/150 Mbs?

Question

The iPad boasts 5 antennas. But It seems only 1 or 2 antennae are enabled to work. I put my iPad right beside the Airpot Extreme router, the connection speed via 802.11a/n at 5GHz never exceeds 72MB, no matter how close it is to the base station. My MacBook Pro 15-inch can achieve a speed of 270MB, and my Airport Express used to extend the range can also connect at 270MB.
Then instead of connecting my iPad to Airport Extreme, I connected it to Airport Express (being used as a bridge to extend the range). IPad at 802.11a/n can only achieve a maximum speed of 150 MB.
So I strongly suspect there is something wrong with the firmware of the 2 Apple Routers.

Answer 1

I think there needs to be an understanding of what the IEEE 802.11 standard says. The channel width for all bands is 20 MHz. The 2007 draft n-protocol allowed a channel width of 40 MHz. That was not adopted in 2009 when the n-protocol was approved. The standard now says, including the 40 MHz 2007 draft for the n-protocol:
Protocol / Bandwidth (MHz) / Transfer rate (Mbps)
b / 20 / 5.5, 11
g / 20 / 6, 9, 12, 18, 24, 36, 48, 54
n / 20 / 7.2, 14.4, 21.7, 28.9, 43.3, 57.8, 65, 72.2
n / 40 / 15, 30, 45, 60, 90, 120, 135, 150
So, if you are getting a transfer rate of 150 Mbps your are under the 2007 draft 40 MHz channel width, not the final approved 2009 n-protocol.
The final approved protocol does not support that transfer rate.