= improved throughput performance, more interference prone than single chain, two connectors on board (MMCX/UFL), two antenna connectors (N/SMA), referred to as multiple input multiple output (MIMO)
= less throughput, less interference prone than dual chain, one connector on board (MMCX/UFL), one antenna connector (N/SMA), referred to as single input single output (SISO)
In RouterOS each dual chain radio transmitter can be used in single chain mode.
Another feature added to 802.11N is MIMO technology. By using two antennas in different polarity or by using one dual polarity antenna in one side our MIMO radio can double the aggregate speed and we can reach 300 Mbps in Theory
- from Deltaelectronics presentation, link enclosed below.
You will find further reading here