# 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 Characteristics in Air and Integrated with Drones
Moreover, a similar trend is observed for vertical distances up to \(-85\) dB, albeit with a slightly higher transmission coefficient. Figure 16: Simulated and measured S-parameter results of the proposed antenna after integrating with metasurface in air and attached to a drone: (**a**) transmission coefficient and (**b**) reflection coefficient. Figure 15: The measurement and calibration setup of the antenna in the air at the sub-THz band (77–140 GHz). Figure 17: Reflection and transmission coefficient results when two arrays of the antenna are attached to one drone. Figure 18: Transmission coefficients results of the antenna on two drones with different (**a**) vertical and (**b**) horizontal distances. After investigating the S-parameter results of the antenna both in free space and attached to the commercial drone, the radiation characteristics of the antenna, such as radiation pattern, gain, and axial ratio (AR), should be evaluated. The radiation pattern measurement of the antenna is carried out in a mm-wave chamber, as shown in Figure 19. Figure 20 indicates the simulated and fabricated radiation pattern for Co. and cross-polarization in free space. A good agreement exists between the simulated and measured patterns of the antenna. The antenna's radiation pattern varies between 30\({}^{\circ}\) and 60\({}^{\circ}\) at lower frequencies and is predominantly around 180\({}^{\circ}\) at higher frequencies. The half-power beam widths (HPBW) are approximately 50 and 46, respectively. Figure 19: Radiation pattern measurement of the antenna in the mm-wave chamber. Furthermore, the steering angle ability of the proposed leaky wave antenna is investigated, as indicated in Figure 14:0 It also demonstrates that the antenna can offer a wide range of steering angles with frequencies up to 180\({}^{\circ}\) for D2D and D2G communication. The simulated cross-polarization (X-pol) levels in the vertical plane will not be visible due to their relatively low magnitude, less than \(-30\) dB. It is important to note that, given the random distribution of most wireless devices in the environment, antennas with omnidirectional characteristics, multi-beam capabilities, or those capable of beam steering offer more extensive coverage. Hence, the proposed MIMO LWA is a promising choice for such requirements. Figure 14:1 The simulated and measured electric and magnetic field of the antenna in free space at (**a**) 8.5 GHz, (**b**) 18 GHz, (**c**) 25 GHz, (**d**) 66 GHz, and (**e**) 77 GHz. Figure 22 showcases the simulated and measured outcomes regarding the proposed antenna's gain, radiation efficiency, and axial ratio (AR). The results indicate a consistent AR level below three across the operational frequency range, both in simulation and measurement. Notably, it reveals a maximum gain of 13.8 dBi, consistently exceeding 5.5 dBi across most frequency bands. Furthermore, the antenna demonstrates notable radiation efficiency, surpassing 77% in higher bands and exceeding 85% for frequencies below 80 GHz. Moreover, it illustrates minimal variations in gain for LHCP and RHCP within the operational band, staying below 1.1 dB and 0.5 dB, respectively (although not depicted in figure). However, a marginal inconsistency between the simulated and measured outcomes is discernible in Figure 14:2  
After assessing the antenna's performance in airborne conditions and its successful integration with a commercial drone, the next phase involves evaluating its MIMO antenna capabilities and diversity. Figure 23 displays the variation of the proposed MIMO leaky wave antenna in terms of diversity gain (DG) and envelope correlation coefficient (ECC). As depicted in Figure 23, the proposed MIMO antenna exhibits a notable diversity gain, measuring less than 9.98, indicating its ability to provide improved signal diversity.