# Meta Surface-Based Multiband MIMO Antenna for UAV Communications at mm-Wave and Sub-THz Bands
## 3 Fabrication, Testing, and Comparison of Simulated and Measured Results
### Antenna System Positioning on Drones and Its Assessment for UAV Communications  
Two practical array configurations are considered for assessment: (1) arrays positioned beneath the drone to ensure coverage of the lower hemisphere; (2) antenna arrays located on the drone's sides and tilted at a \(-45^{\circ}\) angle relative to the drone's plane. Each array covers sectors of approximately \(90^{\circ}\), both accumulating \(180^{\circ}\). Before assessing these two configurations, it is better to elaborate on the antennas' 3D radiation pattern at each radiation mode. After evaluating the antenna's radiation in free space, the radiation patterns are defined when the antenna is attached to the drone. The 3D radiation patterns of the proposed antenna in all three modes and different bands are simulated, as shown in Figure 24. The findings displayed in Figures 24 and 25 suggest the presence of conical radiation patterns in the vertical plane (XOZ plane and towards the ground) at the lower bands and dual-directional (both bidirectional and end-fire radiations) beams in the horizontal plane (XOY plane) at higher bands. Figure 23: Diversity gain (DG) and envelope correlation coefficient (ECC) results of MIMO antenna. Figure 24: Antenna’s estimated 3D radiation patterns on a commercial drone at (**a**) 8.5 GHz, (**b**) 10 GHz, (**c**) 18 GHz, (**d**) 25 GHz, (**e**) 45 GHz, (**f**) 66 GHz, (**g**) 77 GHz, and (**h**) 120 GHz. Figure 26 shows the simulation setup for the power received by the receiver drone and tests the antenna performance when it is attached to the drone and the electronic circuitry module. Figure 26a depicts the simulation setup to obtain the received power from the transmitter drone at various distances. The transmitter drone is located at the center of the field. Then, several power receiver probes (shown by blue and green markers in CST software, version 2023) are situated at vertical and horizontal distances from the transmitter drone. They are also located at 45 degrees between each axis. After the simulated calculation, the antenna is attached to the communication module, and the 3D-printed drone is used to see the antenna performance in real scenarios. Figure 27 shows the maximum received power at different locations (both horizontal and vertical distances and various angles) around the proposed antenna at the center. As expected, the received power decreases when the distances increase. However, since the proposed antenna offers circular polarization, it can provide consistent radiation for both left- and right-hand polarization (LHCP and RHCP). The received power is assessed at up to 1 km distances around the transmitter drone. However, we focus more on the drone for indoor communication, such as performing in a large factory. The simulated evaluation of the received power shows that the proposed MIMO antenna can perform perfectly for indoor communication for both ground-to-drone and drone-to-drone communications. Figure 26: The proposed antenna integrated with the drone: (**a**) power receiver probe around the transmitter drone in vertical and horizontal spaces, (**b**) overview of the simulated field test, and (**c**) horizontal assessment of the transmission and receiving power. Figure 25: The simulated radiation pattern of the antenna when it is integrated with the drone at (**a**) 8.5 GHz, (**b**) 10 GHz, (**c**) 18 GHz, (**d**) 25 GHz, (**e**) 45 GHz, (**f**) 66 GHz, (**g**) 77 GHz, and (**h**) 120 GHz. Table 3 shows the comparative performance of several MIMO antennas used for UAV communication. The comparison is made regarding dimensions, operating bandwidth, radiation characteristics (maximum gain and efficiency), coverage, and diversity performance of the proposed MIMO antenna (DG, ECC, and isolation). Table 3 also demonstrates that the proposed antenna system surpasses these recent similar works and has excellent potential as a multiband operating system for both mm-wave and sub-THz communications in UAV applications.