Antenna Diversity
There's a wide variety of how transmit and receive diversity is implemented on various Atheros wireless chips.
Overview
Implementation
Classic transmit and (fast) receive diversity using an external antenna switch
Using an external antenna switch on a MIMO device to add transmit/receive antennas
Programming, Monitoring, Diagnostics
(Slow) External Antenna Switch Diversity on the AR5416 and later 802.11n chips
LNA, Bluetooth and External Antenna Switch Diversity on the AR9285
External and Bluetooth Antenna Switch Diversity on the AR9287 + Bluetooth Combo NICs
Using the per-descriptor TX antenna shift register on the AR5416 and later hardware