There are a wide range of antenna technologies available today. A more recent option is to choose a multi-input multi-output (MIMO) antenna. Though newer, is a MIMO antenna better than a traditional single-input single-output SISO antenna? More is always better right? This is certainly not the case with SISO and MIMO antennas, and like virtually every RF circuit/signal chain, the antenna is a critical component that needs to be precisely specified for a given application and that decision making needs to include the other devices/components in the system.
A SISO antenna is a single-port antenna that has a single driven element, though the antenna could be balanced or unbalanced depending on the design. A MIMO antenna, on the other hand, is an antenna system that consists of at least two distinct antennas. Each of the MIMO antenna elements has a distinct input port that is designed to be driven individually from a MIMO compatible radio. In theory, a MIMO antenna may be driven like a SISO antenna by splitting the power from a SISO radio to the multiple MIMO antenna elements. However, this likely won’t provide substantial benefit, and an appropriate SISO antenna would probably provide better performance, especially considering the intrinsic losses associated with introducing any passive elements in a signal chain.
In order to make the most of a MIMO antenna, a MIMO radio is needed. This could be a WiFi or cellular system that makes use of MIMO technology and spatial multiplexing to provide higher throughput than is possible with a single spatial channel.
The number of MIMO channels, radio hardware/protocol, and channel quality determines the overall throughput gain possible compared to a SISO antenna system. If the radio hardware/protocol or channel quality is poor, then a MIMO system may not provide any substantial benefit over a SISO system. Hence, knowledge of the channel and radio technology are critical in determining if a MIMO antenna is appropriate. If the application is appropriate and the communication link is between two MIMO-equipped nodes, then it is possible to achieve many times the throughput of a comparable SISO communication link. It is important to note that MIMO isn’t necessarily using different frequency bands to increase throughput but is instead using spatial multiplexing to create separate spatial channels with their own communication stream.
Generally, the only reason to employ a MIMO system is to provide greater throughput, possibly to a larger number of devices in a given region. MIMO systems are intrinsically different and should not be confused with beamforming antenna systems, though an advanced antenna system (AAS) may be both MIMO and beamforming capable.