# The Design and Implementation of a Phased Antenna Array System for LEO Satellite Communications
## 2 Antenna Design Challenges for Leo Satellite Communications
This solution for phase shifters brings the disadvantage of a reduced angular resolution and increased complexity of the delay line networks, even if the computing power requirement is not very high. Advantages offered by new technologies based on coherent SDR receivers [20], such as the KrakenSDR project [21; 22], offers a high angular resolution and the capability of simultaneous multi-satellite tracking but requires very high processing power, high system complexity, and consequently long delays. Although this technology allows for very interesting applications, such as radio direction finding, it can also be used for tracking and receiving LEO satellites. The medium elevation range (25-70\({}^{\circ}\)) is often preferred in LEO satellite communications for several reasons. High altitude passes (70-90\({}^{\circ}\)) are rare and brief, with stronger Doppler effects due to maximum orbital speeds. Low elevation passes (0-25\({}^{\circ}\)) have longer durations but suffer from atmospheric absorption, interference, and reflections, particularly at greater distances. At medium elevations, approximately 35% of total transit time, the signal remains more intact with lower losses and less pronounced Doppler effects. Consequently, we proposed the implementation of the 3\(\lambda\)/4 configuration for the antenna array elements, as it inherently exhibits favorable radiation characteristics within this elevation range, enabling the concentration of maximum radiated energy towards this angular interval. The three-quarter wavelength (3\(\lambda\)/4) antenna element offers several advantages that will be highlighted in the following paragraphs. Different studies [23; 24; 25; 26] revealed that compared to other antenna configurations, such as half-wavelength (\(\lambda\)/2) and the widely used quarter-wavelength (\(\lambda\)/4), in the case of the 3\(\lambda\)/4 antenna element, in the radiation pattern's vertical plane, the maximum radiation lobe (main lobe) rises towards medium elevation angles, while preserving its omnidirectional characteristic in the horizontal plane. Additionally, even at low elevation angles, the 3\(\lambda\)/4 antenna gain is superior to, or at least equal to, that offered by the widely used conventional \(\lambda\)/4 vertical monopole elements, but also to that provided by the \(\lambda\)/2 configuration. Furthermore, 3\(\lambda\)/4 vertical monopole elements used together with at least two radial elements arranged symmetrically with respect to their feeding points or used in the variant where they are fixed to a consistent metallic ground plane maintain the impedance at a value very close to 50 Ohms, regardless of the resonant frequency they are tuned to. The physical implementation is relatively simple, and the procedures for tuning those antenna elements and fixing them on the ground plane are not overly complex. Another advantage is related to the radiation pattern in the vertical plane remaining favorable for medium elevation angles. The design, implementation, and testing of such a complex system requires advanced knowledge in the field of antennas and communications. A phased antenna array, based on an original conceptual approach, through incorporating three-quarter wavelength elements and introducing an innovative constructive concept regarding the structuring of other necessary elements for array operation, is proposed in this article. In general, achieving beam steering using a controlled phase-shifting technique in phased antenna array systems is not new, as it has been recognized and implemented in various contexts, including industrial applications. In this paper, the focus was not on the development of advanced beamforming techniques involving the control of both amplitudes and phases using complex mathematical beamforming algorithms. Instead, the primary objective was to demonstrate the system's functionality as a holistic concept in terms of the ability to direct the main radiation lobe in the desired direction, an essential feature for tracking LEO (Low Earth Orbit) satellites.