# Meta Surface-Based Multiband MIMO Antenna for UAV Communications at mm-Wave and Sub-THz Bands
## 2 Materials and Methods
### Simulation
#### 2.1.1 Design Process of the Antenna with a Single Port
With the proposed antenna shape and the enhancement of OSB suppression through an asymmetrical structure, the radiation mechanism of the new antenna is based on the asymmetry principle depicted in Figure 1. When the periodic slots are symmetrically positioned relative to the side walls, the vertically polarized TE\({}_{10}\) mode does not induce any horizontal field in the antenna aperture, as shown in Figure 1a. This principle is utilized by the transverse parts of the mesh-like slots in the proposed design, meaning the electromagnetic waves emitted from the port have polarizations perpendicular to the longitudinal planes of both the antenna and the transmission line. In the case of the stub-loaded LWA, the parallel plates (patch and ground layers) act as a filtering mechanism, permitting only the horizontal field to reach the waveguide aperture, positioned at height, \(m\), from the dielectric interface in space. Thus, the symmetrical periodic structure makes the TE\({}_{10}\) mode nonradiative when \(m\) is sufficiently high. The slots must be asymmetrically positioned to induce a potential difference in the parallel plates. This potential difference generates a horizontally polarized TEM wave, which can propagate to the aperture and radiate into the free space region, as shown in Figure 1b. The longitudinal parts of the mesh-like slots in the proposed design operate based on this principle. Therefore, by adjusting the slot asymmetry, one can control the excitation level of this radiating horizontal wave, thus altering the leakage rate of the TE\({}_{10}\) leaky mode. In contrast, the dielectric inset operates by exciting the TE\({}_{10}\) mode, which is itself horizontally polarized. The TE\({}_{10}\) mode alone is responsible for the antenna's radiation, eliminating the need for introducing asymmetry to induce radiation in the structure, as depicted in Figure 1c. Additionally, altering the slot aperture is the only way to control the inset's leakage rate. However, in this novel design and combination of slots, the leakage rate can be controlled by adjusting the slot asymmetry (spacing between the mesh-like slots and the longitudinal slot) while keeping the inset space value unchanged. After the antenna's characteristic modes and the associated LWA principles were explained and discussed, the design process of the antenna started following the rules and equations presented in the above sections. Figure 2 displays the simulated prototype and antenna dimensions,  
Figure 1: Asymmetry radiation principle: (**a**) TE\({}_{10}\) mode in even structure; (**b**) leaky TE\({}_{10}\) mode in the uneven structure; (**c**) leaky TE\({}_{01}\) mode in even structure (\(\theta\) is the approximated maximum angle of the radiation and the red arrows show the direction of the field) [36]. highlighting each component's crucial parameter in antenna design. As presented in Figure 2, the design process begins by designing one port antenna following each design step shown in Figure 2a-f. When the proposed antenna's characteristics with one port are assessed, it is expanded to a two-port antenna by adding the antenna next to it and applying the neutralization network between them. The design steps are explained as follows, based on what is depicted in Figure 2. In addition, Table 2 shows the dimensions and optimized values of the proposed antenna parts. Each value was optimized after the actual values were obtained using the related equation, and the parametric studies were performed.