卫星载荷I/Q失真对导航信号的影响分析

Impact of Satellite Payload I/Q Distortion on Navigation Signal

卫星载荷射频通道引起的信号畸变是导航信号测距误差主要来源之一,其中星上载荷射频通道上变频器的直流偏置、本振泄漏和相位噪声等非理想特性引起的信号波形畸变严重影响导航信号码相位和载波相位测量精度。基于直接正交上变频方式传输通道模型,以导航信号相关损耗、S曲线过零点偏差、S曲线过零点斜率偏差、星座图、功率谱密度、基带信号时域波形、PLL跟踪抖动作为评估指标,量化分析了变频器非理想特性对导航信号质量的影响。研究结果表明,非理想因素恶化导航信号I/Q正交性和幅度平衡性,导致相关曲线、功率谱密度、码片时域波形发生畸变,影响导航信号测距精度;仿真条件下,相位噪声对导航信号码相位测量精度影响较大,导致PLL跟踪抖动差值可达1.6Hz,且随累积跟踪时间呈上升趋势。上述研究可作为星上载荷射频通道变频器设计及优化参考。

Signal distortion caused by satellite payload RF-channel is one of the main sources of navigation signal ranging error. Furthermore, the signal waveform distortion caused by non-ideal characteristics such as DC offset, local oscillator leakage, and phase noise of the up-converter on the RF-channel on the satellite payload seriously affects the accuracy of the navigation signal code phase and carrier phase measurement. The direct quadrature up-converter transmission channel model was proposed in this paper. The navigation signal was evaluated through correlation loss, S curve bias(SCB), S curve slope(SCS) bias, constellation, power spectral density, time domain waveform of baseband signal and PLL tracking error. In addition, the influence of non-ideal characteristics for converter on the quality of navigation signal was analysed in this paper. The results show that the I/Q orthogonality and amplitude balance of navigation signal are worsen by non-ideal characteristics. In addition, the correlation curve, power spectral density and time domain waveform of baseband signal is worsen. Therefore, the ranging performance has a low accuracy. The influence factor of phase noise has a great impact on the accuracy of the code phase measurement. In addition, the difference of tracking error can reach 1.6 Hz and show upward trend with cumulative tracking time. The research in this paper can be thought of as a reference to the design and optimization of the navigation signal payload RF-channel converter.