**5. Conclusions**

The holography technique and its application in forming the beam in electromagnetic structures are explained in this chapter. Leaky-wave antennas, metasurface reflectors, and reconfigurable intelligent surfaces (RISs) are assessed in this regard. The aperture efficiency of RIS is also studied which is one of the main barriers to industrializing this component in future cellular networks. A comparison is made between the functionality of the smallest building blocks in holographic-base metasurfaces, phased array antennas, and MIMO systems.
