**3. Metalens applications**

### **3.1 Metalens antenna for beamforming massive MIMO**

Metamaterial is usually used to reduce the antenna size and mutual coupling of antenna array, increase the efficiency and bandwidth. In this applications, a

*Metalens Antennas in Microwave, Terahertz and Optical Domain Applications DOI: http://dx.doi.org/10.5772/intechopen.99034*

#### **Figure 2.**

*(a) Schematic of a metalens operating in transmission mode. (b, c) Side-view and top-view of the metalens building lattice as a TiO2 nanopillar on a glass substrate. For the design wavelength* λ*d = 405 nm, 532 nm, 660 nm, the unit cell dimension is U = 180 nm, 250 nm, 350 nm, H = 400 nm, 600 nm, and D vary between 80 to 155 nm. (d) The phase map* φ*(D) of the metalens simulated at* λ*d = 532 nm. The phase map represents the relative phase difference between the nanoposts and the reference point which there is no nanopost. (e) The phase comparison from FDTD simulation of the cell with varying diameter D, and the phase in the single cylindrical waveguide of the fundamental mode (HE11) with the wavelength of 532 nm. (f) Transmission coefficients in complex space at three different wavelengths. The colored points show the amplitude and phase of the transmitted light of the nanopost.*

metalens antenna with substrate integrated waveguide (SIW) feeding structure is present for low-cost broadband antenna for coming 5G massive MIMO applications at 28GHz, as shown in **Figure 4(a)**. **Figure 4(b)** shows that Jerusalem cross (JC) pattern is used as unit cell to form the metalens surface, where the width of JC unit p = 4.6 mm, c1 = 3.9 mm and c2 = 2.7 mm. A double-layer metalens structure is used to enhance the focusing effect and 7 feeding units are aligned to transmit or receive signal from different angles. Both the lens and feeding structure are fabricated with the regular printing circuit board (PCB) process. To scan the beam over the broad range from −25° to 25°, the array of SIW feeding stacked-patch antenna is used as the transmit/receive antenna from different angles. SIW structure in **Figure 4(c)** is often used for better confinement with minor loss above 20GHz. More design parameters could be found in **Table 1**. Metalens antenna could be excited by this feeding antenna mechanism or receive signal from certain angle individually. Finally, the measured results validate the design of the lens antenna well.

Generally, metalens antenna with angular feeding element could be used for the spatial beamforming and multi-beam 5G massive MIMO communication. **Figure 4(e)** shows that the planar lens has the stable focusing performances as well as linear beam scanning angle of ±25°. The arrangement and distance of feeding elements are analyzed on power distribution and the result shows that a linear

#### **Figure 3.**

*Simulation of V-shaped antenna unit. (a) Curves of V-shaped nanoantenna amplitude variations as the antenna thickness t changes for the case of 60°, 90°, 120°, 180°, respectively. (b) Electric field distribution of cross-polarized light of 8 V-shaped nanoantenna.*

uniformly feeding array could be placed accordingly to the scanning angle in free space. The antenna has the measured gain of 24.2 dBi, side lobe level (SLL) less than −18 dB compared to the center feeding port. Metalens antenna could deliver the constant radiation across 26–29 GHz and realizes a beamforming of ±25° with a gain tolerance of 3.7 dB through switching the ports of the feed elements. The lens and the feeding array have been verified easily fabricated by standard PCB procedure, which is promising for the future telecommunication and radar system applications.
