# The Design and Implementation of a Phased Antenna Array System for LEO Satellite Communications
## 6 Performance Evaluation
### Comparative Examples  
The proposed four-element, three-quarter wavelength antenna array is equivalent in terms of polarization, main lobe gain, radiation pattern, and beam steering to a five-element vertical polarized Yagi-Uda antenna, tilted at an angle of 42\({}^{\circ}\), mounted on an azimuthal antenna rotator. The compared far-field radiation patterns of the two antennas in the vertical plane (a) and in the azimuth plane (b) are shown in Figure 16.  
As can be seen, the 5-element Yagi-Uda antenna has a maximum gain of approximately 10.75 dBi. The proposed phased antenna array has a maximum gain close to 12 dBi (the range was approximately from 11.55 dBi at 0\({}^{\circ}\) beam steering angle to 11.97 dBi at other angles), a wider HPBW (62-87\({}^{\circ}\)), depending on beam steering angle, and the main lobe orientation can be controlled electronically, without the need for rotators. Table 1 highlights the comparison between the qualitative aspects of the systems widely used in LEO communications in terms of the phase-shifting techniques used, the complexity of the associated systems, and the types of polarization considered. In light of the analysis presented in Table 1, it is distinguished that the proposed phased antenna array stands out for its high beam direction resolution and fast signal processing capabilities. These characteristics are favored by the use of the phase shift technique based on integrated vector modulators. It is also found that the complexity and cost of the system are reduced compared to other similar solutions, which do not offer significant advantages in terms of azimuth scanning capability and satellite tracking speed for low-orbit (LEO) satellite  
Figure 16: Comparison of simulated radiation patterns for a 5-element Yagi-Uda antenna (plotted in black) and the proposed phased antenna array (plotted in red) in the vertical plane (**a**) and the azimuth plane (**b**), corresponding to 0\({}^{\circ}\) azimuthal beam steering angle. communications reception. These aspects are relevant in the context where the proposed system achieves a balanced compromise between complexity and performance. The analysis of the table reveals that the proposed system offers several advantages, including low processing power requirements, system simplicity, the capability to orient the main lobe to any angle within the range of 0\({}^{\circ}\) to 360\({}^{\circ}\) with high angular resolution (less than 1 degree), and very low delays in signal processing. Regarding the type of polarization, circularly polarized elements are used more often in satellite communications for certain reasons. First of all, the transmitted signal is less affected by changes in the orientation of the satellite. Additionally, it provides satisfactory robustness against fading and interference, which can improve performance in noisy or heavily spatially multiplexed environments. This polarization also allows better isolation between transmitted and received signals, thus reducing cross-channel interference. However, the disadvantages of using circularly polarized elements in phased antenna arrays for LEO satellite reception can involve increased complexity, additional signal loss, and higher costs. On the other hand, the three-quarter wavelength, vertically polarized elements selected for the proposed phased antenna array offer a significantly higher gain, coupled with improved directivity and increased resistance to interference and fading. In Table 1, we note that delay line-based phase shifting has limited angular beam steering resolution due to its predefined structure for phase shifting. This also entails relatively complex design requirements. Additionally, turnstile-type elements chosen by Ibelings [19] are complex, necessitating meticulous management of numerous variables for precise main lobe orientation within the array.