## 1 Introduction  
Medium Earth orbit (MEO) satellites typically weigh between 500 and 1000 kg, carry out at a height above sea level of 900 km, follow an orbit synchronized with the Sun's position, and have elevated levels of power consumption, at around 8 kW. They have a lifespan of approximately four years and come with a hefty price tag of USD 50 to 100 million. As a result, only large companies and government organizations with significant financial resources have been able to build and operate these large satellites. MEO satellites support Earth observation, weather forecasting, mobile networks, and scientific research. A notable example is Formosat-2, the first remote sensing and scientific observation satellite in a sun-synchronous orbit, developed and deployed by Taiwan's National Space Program Office (NSPO). Figure 1 shows a general concept of CubeSat communications (Figure 1). Traditional satellites use large medium-gain antennas, like horn antennas with precise pointing systems, for ground communication. In contrast, CubeSats offer low-cost alternatives that are accessible to the public. These small, lightweight satellites operate in low Earth orbit (LEO) and utilize readily available, commercial off-the-shelf (COTS) components. Three typical CubeSat configurations of varying sizes exist, such as 10 cm\({}^{3}\) for a 1U CubeSat, 10 \(\times\) 10 \(\times\) 20 cm\({}^{3}\) for a 2U CubeSat, and 10 \(\times\) 10 \(\times\) 30 cm\({}^{3}\) for a 3U CubeSat (Figure 2). They weigh between 1 and 6 kg and have low power requirements of around 2 W. The Tokyo Tech 1U CubeSat, CUTE-I, is a prominent example of CubeSat technology. Developed by TIT, in 2003, it weighs 1 kg and operates in LEO at an altitude of 820 km. They created it for communication and sensing operations [1]. The Telemetry, Tracking, and Communications (TTC) subsystem is critical to a CubeSat, ensuring reliable communication with the ground station for continuous data exchange. The subsystem's antenna facilitates the transmission of telemetry and scientific data, such as images, while also receiving commands. Designing CubeSat antennas is challenging due to stringent constraints on size (1U), weight (under 1.3 kg), and power consumption (but to a lesser extent, at 2 W) while still requiring great gain and broad BW [2]. Traditional CubeSat communication systems often rely on omnidirectional mono or dipole antennas that operate in the UHF or S-band frequencies. Although relatively simple and robust, they offer limited gain and directivity, resulting in lower data rates and increased susceptibility to interference. As mission requirements evolve to demand higher data throughput and more robust communication links, there is a pressing need to enhance the performance of CubeSat antenna systems. Beam-steering and beamforming technologies have emerged as promising solutions for these challenges. Beam steering involves directing the antenna's main lobe toward a specific direction without physically moving the antenna. At the same time, beamforming utilizes multiple antenna elements to electronically shape and control the radiation's pattern. These techniques can significantly improve communication performance by increasing antenna gain, enhancing link reliability, and reducing interference. Figure 1: CubeSat communications. Figure 2: CubeSat designs: (**left**) 1U; (**middle**) 2U; (**right**) 3U [1]. Modern antenna design improvements have resulted in the development of various beam-steering and beamforming systems suitable for CubeSats. For instance, metasurface-based antennas have been explored for their ability to steer beams passively, offering an ideal compact and power-efficient solution for the constrained CubeSat environment. These antennas utilize engineered surfaces to manipulate electromagnetic waves, enabling beam-steering capabilities without the need for complex feeding networks or mechanical parts [3]. In addition, implementing beam-steering and beamforming systems in CubeSats is challenging.