**4. Comparison between holographic, MIMO, and phased-array beamforming**

Consider a case when printed patches are used in three different structures, i.e. a holographic-based metasurface, a phased-array antenna, and a MIMO system. The only common thing between these three is the repeating geometry of patches across the structure. The detailed functionality of these patches is as below:


**Figure 10.** *(a) A multibeam metasurface reflector, (b) a tilted-beam phased-array antenna and (c) a 4-element MIMO system.*

<sup>1</sup> Note that this is not just limited to the holography, other methods like GSR can also be used.

*Holographic Beamforming DOI: http://dx.doi.org/10.5772/intechopen.112467*

• MIMO system: the size of patches is again in the scopes of half-wavelength to make a resonating element. However, the spacing between elements is managed to decrease the coupling between elements. When there is a port for each element, this low mutual coupling can decrease the cross-correlation between the ports which can be a good candidate to be used in MIMO systems. As each element is functionally separated from the others, it is common to be called an embedded element. In this case, each embedded element has its own radiation characteristics. A schema of a 4-element MIMO system is presented in **Figure 10(c)**. This structure has four separate apertures considering **Figure 1**.
