# The Design and Implementation of a Phased Antenna Array System for LEO Satellite Communications
## 1 Introduction  
During the past years, the satellite communications market is expected to reach USD 160.65 billion by 2030 [1] and will continue to grow in the next years, sustained by the development of new technologies. The number of applications of satellite communications extended NB-IoT (Narrow Band Internet of Things) connectivity from space to remote, isolated geographical areas. The number of LEO (Low Earth Orbit) satellites gained immense popularity due to some distinct advantages in satellite communications, which can compensate for the shortcomings associated with communications using GEO (Geostationary Earth Orbit) and MEO (Medium Earth Orbit) satellites. The main advantages include reduced latency due to short distances between satellites and Earth, improved global coverage given orbital trajectories, and the flexibility and scalability of LEO systems that can quickly adapt to user requirements by adding or reconfiguring existing satellites. These features, along with the extensive use of multiple frequency bands, help improve performance in congested environments such as those found in various IoT architectures. Additionally, ensuring a greater immunity to interference and oversaturation of radio frequencies by using a large number of satellites with the availability of several frequency bands can lead to better performance in congested radio communications scenarios specific to different IoT architectures. Moreover, the latency associated with GEO satellite communications creates problems in latency-sensitive applications such as real-time communications (video conferencing), financial transactions, applications that include Augmented Reality (AR) and Virtual Reality (VR), Internet of Things (IoT), medical telemedicine, and autonomous transportation. Therefore, GEO satellites are mainly used for one-way communications, such as satellite television, monitoring of Earth's natural resources, and other reduced latency-sensitive applications [2]. The above performance aspects, as well as the increasing requirements for enhanced transfer rates via increased data throughput efficiency and fast global coverage, have been the determining factors for industry-leading companies to invest in the development of large LEO satellite constellations. The main objectives behind these initiatives include providing fast and secure communication services and high-speed Internet, including in rural, isolated areas or with poor data connectivity, remote observations, and navigation. Companies such as SpaceX with the Starlink [3] constellation, OneWeb (Oneweb Network Access Associates Limited--London [4]), Amazon with the Kuiper project [5], and the Hongyan constellation developed by China Aerospace Science and Technology Corporation (CASC) [6] have invested significantly in the development and launch of LEO satellite constellations. The frequency bands used by LEO constellations start from VHF (30-300) MHz and UHF bands (300 MHz-3 GHz) and continue to Ku-band (12-18) GHz, Ka-band (26.5-40) GHz and V-band (40-75) GHz. However, there are certain disadvantages associated with using these LEO satellite constellations. The large number of satellites required for a large geographical coverage (hundreds or even thousands of satellites) can lead to very high costs and risks of collision with other satellites or space debris. Additionally, compared to GEO satellite communications, LEO satellite communications can be affected by the interference caused by the general state of the weather due to the lower altitude, and on the other hand, the latency can vary depending on the location of the user or the ground station. Last but not least, there is the need for an extensive network of ground stations, including antennas or antenna systems that can track satellites throughout their entire orbit. Despite these drawbacks, LEO constellations remain an attractive option in the field of satellite communications, providing a viable alternative to complement terrestrial communications infrastructure to expand the connectivity area.