星载微波辐射计天馈系统噪声温度分析

星载微波辐射计在轨运行时，影响天线温度的因素与天馈系统的空间与时 间的不稳定性有关。在最坏情况下，裸露在卫星舱外的天线物理温度的变化值可达±
150℃，而且太空环境和卫星舱内环境存在一定的温度差异，使得连接天线与开关 的波导存在一定的温度梯度。依次分析了反射面对观测信号传输的影响，天线馈源物理 温度在-150℃～150℃范围内时的噪声温度，温度梯度对计算连接波导噪声温度的影响。利 用上述的分析结果，确定了天馈系统的在轨测温方法以满足星载微波辐射计精确定标的要求 。

Analysis on the Noise Temperature of Antenna and Feed of a Spaceborne Microwave Radiometer

The antenna temperature of a spaceborne microwave radiometer is affected by the spatial and temporal instabilities of the antenna and feed subsystem. In the worst cases, the physical temperature of the antennas outside the satellite can change from -150℃ to +150℃, which will lead to big changes of the thermal emission noise temperature of a lossy antenna. Additionally, the big difference of the temperature between outside and inside of the satellite capsule can give rise to temperature gradient on the waveguide linking the antennas and the microwave receiver of the system. The assumption or measurement error of this temperature gradient can lead to error of the calculated noise temperature generated by the Ohmic loss of the waveguide. In this paper, how the reflection plane affects the "observed" signal , noise temperature of the antenna with a temperature changing from -150℃ to +150℃ for given radiation efficiencies and the impact of the temperature gradients of waveguide on the estimation error of thermal emission noise temperature of the waveguide are analyzed sequentially. Based on the analysis, some requirements and suggestions on the temperature measurement of the antennas and the waveguides are proposed to ensure the calibration and measurement accuracies.