# Meta Surface-Based Multiband MIMO Antenna for UAV Communications at mm-Wave and Sub-THz Bands
## 1 Introduction
### The State of the Art and Originality of Study
The utilization of mm-wave networks is crucial for supporting high-speed, real-time communication links, while the UAV operates in-flight, offering essential wireless connectivity in hotspot areas. In addition to mm-wave networks, the antenna addresses communication sub-systems spanning multiple frequency bands, including the X-band (frequently used for applications above the atmosphere, such as radar and fixed and mobile satellite communication), K-band (for satellite receiver communication), and bandwidths operating within the 5G mm-wave and future 6G systems. This extensive frequency coverage supports various communication needs, including down-and-up link communications (drone communications to ground and satellite) and communications among drones. This comprehensive coverage facilitates UAV-assisted communication links, which is crucial for a broad range of applications, such as the most probable mm-wave and sub-THz frequency range for the future 6G systems. To sum up, the contributions of this work are summarized as follows:  
1. A significant feature of the proposed antenna is its use of a coplanar proximity technique combining capacitive and inductive loading, enhanced by mesh-like slots and a vertical slot to mitigate open-stopband (OSB) issues. These design elements enable the antenna to radiate broadside and bidirectionally. Additionally, H-shaped slots on a strip enhance port isolation, and a coffee bean metasurface (MTS) boosts radiation efficiency and gain. Compared to other shapes like rectangles and rings, this unique structure can support multiple resonant modes, potentially enhancing the operational bandwidth due to its asymmetrical geometry. It also helps distribute the electromagnetic fields, reduces losses, enhances radiation efficiency, and offers effective CP. 2. This approach enables a compact, planar configuration suitable for installing unmanned aerial vehicles (UAVs). The antenna provides adaptable radiation patterns and the capability to steer beams across various frequency bands, catering to the signal coverage needs in both the upper and the lower half-spaces, meeting the demands of UAV missions. A significant achievement of this design lies in its attainment of a broad bandwidth within the mm-wave band and sub-THz, making it highly appealing for facilitating high-data-rate communications in UAV-assisted mm-wave scenarios. 3. It can offer high data rates to D2G base stations and allows for high data rate transmissions, enabling the transfer of high-definition video, real-time telemetry, and other data-intensive applications. In addition, higher-frequency bands are less crowded, reducing the likelihood of interference and improving the reliability and quality of communication. The high directional gain of the antenna enhances the effective communication range and signal quality by focusing the signal that is going toward the base station, reducing power requirements, and increasing the signal-to-noise ratio. For D2D communications, it can offer efficient swarm communication (high data rates at mm-wave and sub-THz), low latency (crucial for time-sensitive operations such as formation flying and collision avoidance), and directional communication (high directional gain helps in maintaining robust links between specific drones in a swarm). Last but not least, in D2S communications, the proposed antenna can be beneficial for long-range communication due to the high directional gain, higher BW, and the X-band, higher-frequency bands, which can support high bandwidth communication, and polarization flexibility (circular polarization helps reduce signal degradation due to atmospheric conditions and maintains consistent communication quality with satellites). The paper's structure is as follows: Section 2 elucidates the proposed multiband antenna's geometric arrangement. Section 3 expounds the antenna's operational principles. Subsequently, Section 4 furnishes performance metrics of the antenna, facilitating comparative analysis. Lastly, the paper is concluded by summarizing the study's findings.