What is a MIMO antenna?

Hi all,

Can anyone provide a basic introduction of the MIMO antenna? I mean that when thinking about designing a MIMO antenna, what the parameters of the antenna we should look at? S-parameters? Patterns? Gain? Or other else.....

Thanks in advance.

Strictly, there's no such thing as a "MIMO" antenna, as the principle relies on two or more antennas to work. Historically, it was noted that a wireless signal would follow multiple paths from path A to B due to reflections etc with phase shifts and what not as a nasty side-effect. Some clever folks figured out that if you would actually use these different paths you would send different data on path A and B to increase bandwidth. So, more than one antenna is used and each antenna is supposed to follow a slightly different "path".

AFAIK, antennae used in Wifi MIMO systems are pretty standard, the one thing to take care of is that radiation patterns are different. If you'd place two dipole antennae in the same way, the "paths" would not be all that different. So, you'd place the two antennae as far away from each other as the device would allow and introduce an angle between them as well...