# 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  
Figures 13-15 depict the simulated setup, the measurement setup in MW/mm-wave, and the measurement setup at sub-THz of the proposed antenna attached to drones (similar to industrial drone: an accurate 3D model for a commercial drone downloaded from [42]). It is a typical dual-copter with a diagonal dimension of 18.50 \(\times\) 9 cm\({}^{2}\). It is suitable for various conditions, such as horizontal and vertical movements between two drones and having two antenna arrays on the drone. The impact of the drone's structure on the antenna parameters is subsequently assessed. Typically, larger drones are constructed from carbon fiber. However, in simulations, we employ PEC material for the conductors and acrylonitrile butadiene styrene (ABS) for the drone section to streamline the model and maintain the comparable characteristics. This approach also allows us to investigate whether the influence of the drone's frame becomes more severe at higher frequencies. The white compartment beneath the black drone and the thinner layer beneath the drone are made of Zetamix. An additional dielectric layer of Zetamix is considered in the measurement assessment. This layer is 3D printed using Zetamix filament (the Zetamix Epsilon range of products contains three filaments, each with different permittivity going from 2.2 for the lowest to 7.5 for the highest; these products are characterized by their low dielectric losses  
Figure 12: The single-element coffee bean metasurface’s characteristics: (**a**) S-parameters results; (**b**,**c**) permittivity and permeability results; (**d**) single element of the coffee bean. and high heat resistance for enduring up to 110 degrees Celsius HDT). It was mentioned that the drone was 3D printed using ABS material with a dielectric constant of 2.2. After 3D printing, the lowest layer of the drone faces the antenna, which is 3D-printed using Zetamix. The reason for choosing Zetamix is its dielectric constant of 7.5, which is in a similar range to that of polyvinylidene fluoride (PVDF) (\(\varepsilon_{r}\ =\ 6\)-9). PVDF is one of the most used materials for building a random body. Figure 14: The measurement setup of the proposed antenna in the air at microwave (up to 10 GHz) and mm-wave (up to 30 GHz) bands: (**a**) without a drone and (**b**) with a drone. Figure 13: Simulation setup of the proposed antenna: (**a**) beneath view, (**b**) upper view, (**c**) two arrays of the proposed antenna on one drone, (**d**) two drones and antenna systems with vertical space, and (**e**) two drones and antenna systems with horizontal space. The simulated and measured reflection and transmission coefficient results of the antenna for the conditions presented in Figures 13-15 are depicted in Figure 16 both in the air and when attached to a commercial-sized drone. A reliable and excellent agreement exists between the simulated and measured results. Furthermore, as explained before, all the antenna resonances and modes were obtained in the simulated and measured results. Wide BW is achieved for the lower and higher antenna modes and high isolation of more than 25 dB is also achieved with and without drone integration. Figure 17 illustrates the reflection and transmission coefficient results obtained when two arrays are attached to a single drone. The reflection coefficient results did not change dramatically, maintaining a high isolation of more than 30 dB between the ports. The transmission coefficient results for the antennas on two drones, considering various vertical and horizontal distances between them, are presented in Figure 18. This figure demonstrates that the transmission coefficient level decreases as the distance between the drones increases. For instance, at a horizontal distance of 25 m, the transmission coefficient drops to \(-90\) dB.