# The Design and Implementation of a Phased Antenna Array System for LEO Satellite Communications
## 2 Antenna Design Challenges for Leo Satellite Communications  
The types of antennas used in GEO satellite reception are usually parabolic antennas of various sizes, which meet specific gain and bandwidth requirements. The wide range of MEO satellites orbiting altitudes led to the need to use a variety of antenna types, depending on the applications pursued; among these types worth mentioning are parabolic, patch (flat), helix (spiral), Yagi (directives), and other types of antennas. To receive signals from LEO satellites in the 435-438 MHz frequency band, several types of antennas are commonly used, including Yagi, Helix, patch, and SDR (Software-Defined Radio) reception antennas. Although this frequency band was initially allocated (1930s) for radio amateurs, with the beginning of modern technological development (1960s-1970s), interest in the use of outer space for communication and research purposes increased. Both radio amateurs and researchers began to use this frequency band for communications with research satellites and conducting experiments in the space field, which include the use of data from various types of sensors mounted on satellites, various experiments like communications with space crews, microgravity, navigation, and others). Starting with the year 2000, the standardization and development of small satellites (CubeSat, PocketQube, and others) led to the current use of this frequency band for communications with these research LEO satellites. The Yagi antennas, due to their remarkable gain and directivity, are commonly employed to achieve expansive azimuthal coverage and track Low Earth Orbit (LEO) satellites to maintain reception integrity. Mechanical systems, commonly referred to as rotators, are used to facilitate this functionality. These rotator systems have many disadvantages, like damage due to rapid wear of the mechanical elements, damage caused by environmental conditions, and the need for frequent and regular maintenance, which leads to low performance in poor weather conditions. With the intention of mitigating or overcoming these disadvantages, alternative versions based on different concepts were explored and experimented with. Among these breakthroughs is the development of phased antenna arrays [11; 12; 13; 14; 15; 16], which emerged as a game changer in the field of satellite communications. Due to their characteristics and the advantages offered, phased antenna arrays can represent successful candidates for implementation in future specific ground stations for LEO satellite communications. A phased antenna array is a compact system of antennas whose directivity can be controlled electronically without requiring mechanical elements to change their position. That is why it can be called a static antenna with electronically controllable directivity. In a phased antenna array, the radiating elements can be arranged in certain topologies, depending on the specifics of the application, and using various methods of controlling the phase and/or amplitude of the feeding signals of each element, the maximum radiation can be oriented in the desired direction. One of the proposed projects of the Libre Space Foundation aimed to replace the rotator-based antennas, already in operation within distributed earth stations mentioned in [17; 18], with four-element helix phased antenna arrays to improve LEO satellites reception and, at the same time, provide the advantage of electronic beam steering control, without the need for moving mechanical components. On the other hand, the creation of a four-element helix phased antenna array involves many variables that are very difficult to manage, starting from the design until bringing it into operation. Another approach is presented in [19], which addresses the use of delay lines as a method of achieving phase shifts between the feeding signals of the antenna array elements.