The results of navigation spacecraft observations with asymmetry of the amplitude patterns of onboard antenna feed systems

The aspects of monitoring the energy characteristics of radio navigation signals of the global navigation satellite system (GLONASS) have been considered. It has been noted that the power of the incoming radio navigation signal in the lower atmosphere depends on the parameters of the onboard antenna system of the navigation spacecraft, primarily, on the shape of the antenna amplitude pattern. The amplitude pattern of the onboard antenna of the spacecraft has a complex shape, and in order to compensate for changes in the power of the radio navigation signal due to the navigation spacecraft moving away from (or approaching) the signal user, the shape of the amplitude pattern should be axisymmetric, i.e., resembling a figure of revolution. Based on regular monitoring of the energy characteristics of the GLONASS radio navigation signals, the shapes of the amplitude patterns of the onboard antenna feed systems of the spacecraft from the orbital group have been evaluated. As a result, asymmetry in the amplitude patterns of some spacecraft has been detected. It has been shown that the asymmetry of the amplitude pattern leads to a dependence of the power of the incoming radio navigation signal on the spacecraft aspect angle, i.e., the position of the spacecraft emitting antenna system relative to the signal user. The probable cause of such asymmetry has been identified as the gradual aging of the active devices in the antenna feed path. The obtained results indicate the need for regular and prompt monitoring of the energy characteristics of radio navigation signals in the lower atmosphere. The observed effect of asymmetry in the amplitude patterns should be taken into account when developing spacecraft antenna feed systems.