Typically, dual polarization is accomplished at -45º and +45º using a linear or planar array of antenna elements that can include dipoles, monopoles, patch, and slot antennas. Polarization is often controlled through a SPDT switch, exciting either the +45º polarized wave or the -45º polarized wave. A sector panel antenna, for instance, could include three ±45° polarized panel antennas where each antenna can also be leveraged for MIMO techniques. Other examples include 360º coverage through the use of four dual polarized antennas with separate feeds for horizontal and vertical polarities.
Separate antenna or combined in one package
Typically, linearly polarized omnidirectional antennas are used in MIMO systems. The choice of antenna depends on the available size where chip and/or PCB antennas would be required in highly integrated user equipment (e.g., handsets, tablets, etc.) while, higher gain, rubber duck antennas could be leveraged in for equipment such as access points and routers (Figure 4). The higher the frequency of operation, the closer the antennas can be moved towards one another while still being able to take advantage spatial diversity. For more industrial applications, custom-built radomes can encase an antenna assembly while protecting the internal circuitry from harsh weather elements (e.g., wind, moisture, salt fog, etc.).