Are two antennas better than one?

Access points that have two antennas use a diversity algorithm to sample signal and select the antenna receiving the strongest signal. That same antenna will then be used to transmit the next outgoing signal. When signal strength changes or retransmission is necessary, the AP may switch to the other antenna, dynamically reacting to changes in the environment that affect RF propagation.

Diversity antennas help overcome a phenomenon known as multi-path, where a transmitted signal bounces off obstructions and arrives at the receiver at slightly different times. An AP with two antennas operating in diversity mode will nearly always deliver more reliable service (and sometimes higher throughput) than an AP with just one antenna. Antenna and radio quality does vary, so you can't just assume that a single-antenna AP from vendor X will under-perform a dual-antenna AP from vendor Y. On the other hand, only the most entry-level APs have one non-removable antenna, so you will usually be better off buying an AP with antenna diversity.