Ubiik Mimomax uses 2 x 2 MIMO (Multiple Input Multiple Output) to allow our radios to deliver twice the capacity in narrowband channels than SISO (Single Input Single Output) systems.
In a MIMO system, you have independent data streams from each transmit port in the radio. In order for these two transmit signals to be received correctly at the other end, the path from each transmit port to the receiver ports of the other radio needs to be decorrelated.
What do we mean by decorrelated?
Scattering or multipath occurs when objects in a path reflect radio signals. In a path with absolutely zero scattering, the horizonal signal you send, for example, would be the horizontal signal you receive. However, in the more likely scenario of having objects in the path, coupling occurs between the vertical and horizontal signals. One of the biggest challenges in RF link design is successfully capturing a signal in an imperfect RF environment. Cross-polarization is an excellent solution to this problem.
In terms of boosting RF performance, the ability to decorrelate signals, even when the path doesn’t decorrelate the signals for you, is one of the biggest advantages gained through the use of cross-polarized antennas.
Can you not just use single polarized antennas?
If you desire the capacity benefits of a MIMO system, but choose not to use a single, integrated cross polarized antenna, you would need to mount two antennas instead – one mounted horizontally, one mounted vertically.
While spatial diversity can be achieved through the use of multiple single polarized antennas, there are some clear downsides to this approach: 1) the extra cost of buying two antennas 2) additional space required on the antenna tower to mount two antennas instead of one cross polarized one 3) the requirement for enough spacing to build in the isolation which equates to the decorrelation, and 4) urban areas may have strict aesthetic restrictions and so fewer antennas may be preferable.