The importance of having high levels of reliability in Global Navigation Satellite Systems (GNSS) signals has increased gradually in recent years. Among other factors, evaluating the available power and its spatial characteristics at the user location is a key task as part of signal quality verification processes. Due to a diversity of factors, the transmitting antennas of GNSS satellites may exhibit a non-nominal on-orbit performance. As a result, the effective isotropically radiated power of navigation signals may be affected, e.g., due to azimuthal asymmetries in the antenna gain pattern. If not analyzed and handled properly, such irregularities may lead to the use of weak signals from a given satellite, possibly resulting in non-admissible positioning errors. The present contribution aims at the analysis of the on-orbit performance of GNSS satellite antennas, using data from the Galileo system as a case study. Employing reconstructed gain patterns, a set of metrics is defined, which intend being used as performance evaluation values. In addition, the concept of antenna performance stability is explored by analyzing changes over time of reconstructed gain patterns. Results using data from the operational Galileo satellites (up to the beginning of 2019) have been obtained. From the computed example reconstructed patterns, gain variations below 0.5 dB and azimuthal asymmetries at the 0.6 dB level (95%) were found for most of the analyzed satellites. Likewise, the obtained results suggest the occurrence of an event that altered the nominal performance of the antenna of Galileo satellite 0102 during the first years of operation. The presented tools and results may be of particular interest for applications requiring navigation signal power monitoring tasks, such as GNSS reflectometry or safety–critical systems.

中文翻译：

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利用重建的增益方向图分析伽利略卫星天线的在轨性能

近年来，在全球导航卫星系统（GNSS）信号中具有高度可靠性的重要性已逐渐提高。除其他因素外，评估用户位置的可用功率及其空间特性是信号质量验证过程的关键任务。由于各种因素，GNSS卫星的发射天线可能会表现出非标称的在轨性能。结果，例如由于天线增益模式中的方位角不对称性，导航信号的有效各向同性辐射功率可能受到影响。如果不进行适当的分析和处理，这种不规则现象可能导致使用来自给定卫星的微弱信号，从而可能导致不允许的定位误差。本文稿旨在利用来自伽利略系统的数据作为案例研究，对GNSS卫星天线的在轨性能进行分析。利用重构的增益模式，定义了一组度量，这些度量旨在用作性能评估值。此外，通过分析重构增益模式随时间的变化来探索天线性能稳定性的概念。使用来自伽利略卫星的运行数据（截至2019年初）获得了结果。从计算出的示例重构模式中，对于大多数分析的卫星，发现增益变化低于0.5 dB，方位角不对称度为0.6 dB（95％）。同样 获得的结果表明，在运行的最初几年中发生了改变伽利略卫星0102天线标称性能的事件。对于需要导航信号功率监视任务的应用（例如GNSS反射测量法或安全性至关重要的系统），提出的工具和结果可能会特别感兴趣。