## 4 Antennas for Beam Steering and Beamforming
### Beam-Steering/Beamforming Techniques and Their Possible Features for CubeSat Communications
The antenna comprises a \(1\times 4\) linearly polarized array fed by a power divider and a coaxial connector. A reconfigurable FSS superstrate was mounted above the antenna to control the radiation pattern dynamically. This configuration allows for adjustable beamforming, enhancing the antenna's adaptability in various communication scenarios. The reconfigurable FSS enables real-time pattern modification, offering potential benefits in flexible beam-steering applications. However, the complexity of integrating the FSS with the antenna array and the potential of an increased system size present challenges. Additionally, the performance of the reconfigurable FSS in terms of bandwidth and efficiency needs further evaluation to ensure its suitability for practical applications. While promising, the design's effectiveness in dynamic beamforming scenarios, such as those encountered in CubeSat communications, requires further investigation. Reference [90] proposes a beam-reconfigurable multi-antenna system utilizing beamforming technology to enhance UAV-to-everything (U2X) communications. The system integrates multiple antennas with phase control techniques to reconfigure radiation patterns, dynamically improving the communication reliability and coverage. The system enhances signal strength by employing beam-combining and mitigating interference, making it suitable for various UAV applications, including surveillance, disaster response, and remote sensing. This approach's key advantage is its adaptability to changing environments, ensuring stable connections despite UAV mobility. However, the implementation faces challenges such as increased system complexity, power consumption, and potential hardware limitations in real-time beam adjustments. While effective for UAV communications, its direct applicability to CubeSat beamforming requires further exploration, as CubeSats operate under stricter power and size constraints. Nonetheless, the study provides valuable insights into beam-reconfigurable designs that can be adapted for space-based communication networks. Reference [91] introduces a pattern-reconfigurable integrated array antenna leveraging a coding metasurface. This design integrates a coding metasurface with an antenna array to achieve dynamic radiation pattern reconfiguration. By adjusting the coding sequences of the metasurface elements, the antenna can steer beams and modify radiation patterns without mechanical movement. This approach offers a low-profile and efficient solution for applications requiring adaptable beam steering, such as wireless communications and radar systems. However, the reliance on electronic reconfiguration introduces challenges related to control complexity and response time. Additionally, the performance in terms of bandwidth and efficiency under different operational conditions requires further evaluation to ensure its suitability for practical applications. While promising, the design's effectiveness in dynamic beamforming scenarios, such as those encountered in CubeSat communications, also requires further investigation. Reconfigurable transmit array antennas have also garnered attention for their beam-steering capabilities. A comprehensive review in Ref. [92] highlights the recent developments and challenges associated with these antennas. The study discusses methods involving tunable materials and electronic components to achieve dynamic beam steering. The challenges include the complexity of the design and the potential increases in the system's cost. Despite these hurdles, the outcomes demonstrate enhanced beam-steering performance, making reconfigurable transmit array antennas a viable option for modern communication systems (Figure 8). Furthermore, in the realm of wireless applications, reconfigurable electromagnetic surfaces have been explored to enhance beam steering. For instance, the research published in Ref. [93] introduces an innovative approach using reconfigurable electromagnetic surfaces to achieve beam steering in reflectarray structures.