integral antennas in MOST laptops - how, what, why?
Can someone tell me what exactly are the two integral antennas in MOST laptops, assuming you have a b,g,n WLAN card/adapter? Is one for b/g and one for n (both at 2.4G)? I'm assuming that if you have a 3 antenna card that one antenna is b/g, one is n(both at 2.4G), and one is 5G (a, n) - is this correct? I'm trying to get this sorted out before I order a new/different WLAN card. I'm thinking of purchasing Intel® Centrino® Advanced-N 6230 or the Intel® Centrino® Advanced-N 6235
Your assumptions are incorrect.
The multiple antennas are for MIMO (Multi Input, Multi Output) use. One antenna will be used when using the a, b and g protocols. All antennas will be used with n and the more the merrier here. ISTR that you need three to get a 300Mbps connection and two restricts you to a maximum of 150, the third antenna being used to provide doubling of either the transmit or receive channel as required. Cue others correcting my assumptions/interpretations here(!)
Now, many laptops only have two antennas installed as standard, so fitting a three antenna card would require the installation of an additional antenna. You'll find that many three antenna cards come provided with an antenna for this reason.
The antennas are unrelated to speed in that the number of radio chains will determine what you are actually able to transmit. In optimal conditions you should be able to get 150Mbps per radio. It really depends on your WLAN adapter's construction and configuration with the AP. In a mixed environment with b/g networks you wont get near that much throughput.