液氮温区高精度宽带可变噪温噪声源研究

The cryogenic microwave receiver front-end with extremely high sensitivity is the core subsystem which is applied to deep space detection, super remote aerospace measurement and control, high-performance radio astronomy observation, etc, and the high precision noise source is the key equipment to test the extremely low noise temperature of the receiver front-end. The common solid state device noise source can’t realize the measurement of the extremely low noise temperature due to its great uncertainty; The hot-cold load noise source filled with liquid nitrogen is of high precision, whereas which is only limited to the relatively narrow wave-guide bandwidth, so we need multiple systems to cover broadband test, and it’s inconvenient to use. The project researches for the low insertion loss adiabatic wide-band microwave coaxial transmission line and the microwave black-body load which are working at the temperature of liquid nitrogen, which is used to substituting for cryogenic adiabatic wave-guide and wave-guide load and broadening the operating bandwidth greatly. Through analyzing the electromagnetic filed and thermal filed to research for temperature and insertion loss distribution of cryogenic microwave coaxial transmission line, combined with microwave test of low temperature and low loss, distributed high precision temperature test and real-time precision variable-temperature Stirling equipment which is working at the temperature of liquid nitrogen, researches for new multi-octave liquid nitrogen temperature region’s broadband high precision program-controlled variable-temperature noise source and calibration model, which can output arbitrary noise temperature of 65K~200K at any frequency point between DC~18GHz working band with the uncertainty of ±1K, and can realize the high precision test of extremely high sensitivity microwave receiver front-end whose noise factors less than 0.2dB by using the polymorphic method.

具有极高灵敏度低温微波接收前端是深空探测、超远程航天测控、高性能射电天文观测等系统的核心子系统，已在各个航天大国中逐步实现工程化应用，而高精度噪声源是测试此类高灵敏设备的极低噪声温度的关键设备。常用的固态器件噪声源由于自身不确定度大，无法实现对极低噪声温度的测量；而加注液氮的冷热负载噪声源，精度虽高，但仅限于波导带宽，带宽相对窄，需要多套系统才能覆盖宽带测试，且使用不方便。本项目研究新型可工作于液氮温区的低插损绝热宽带微波同轴传输线及微波黑体负载，通过电磁场和热场联合分析，建立低温温度及低插损分布模型，同时结合可工作到液氮温区的斯特林实时精密变温装置，研究新型液氮温区多倍频程宽带高精度程控可变噪温噪声源并建立定标模型，可在DC~18GHz内任意频点输出65K~200K任意噪声温度，通过多态法可实现对噪声系数小于0.2dB的极高灵敏度微波器件及设备进行高精度噪温测试，不确定度小于±1K。

项目背景：具有极高灵敏度低温微波接收前端是深空探测、超远程航天测控、高性能射电天文观测等系统的核心子系统，已在各个航天大国中逐步实现工程化应用，而高精度噪声源是测试此类高灵敏设备的极低噪声温度的关键设备。常用的固态器件噪声源由于自身不确定度大，无法实现对极低噪声温度的测量；而加注液氮的冷热负载噪声源，精度虽高，但仅限于波导带宽，带宽相对窄，需要多套系统才能覆盖宽带测试，且使用不方便。为了解决低温物理噪声测试问题，本项目研究可工作于液氮温区的低插损绝热宽带微波同轴传输线及微波黑体负载，为低温物理的噪声测试奠定基础。. 主要研究内容：（1）建立噪声源定标理论模型，结合电磁场和热场联合分析，研究传输线与负载阻抗失配、传输线插入损耗、传输线温度分布等因素对定标的影响，并在此基础上设计一套标准变温负载。利用变温负载产生噪声功率，通过低温低插损绝热传输线连接到输出端面，并构建了一套标准噪声源。（2）根据标准噪声源定标理论模型，推导出定标方程，将复杂的定标方程转换为对核心部件物理模型的研究，研究了黑体负载及新型低温微波传输线等的物理模型，研究了液氮温度下的温度非线性分布及低温状态的极低插入损耗分布。. 重要结果、关键数据及科学意义：完成了变温噪声源系统设计和系统不确定度分析。实验结果显示，所设计的噪声源可在DC~18GHz内任意频点输出65K~200K任意噪声温度，通过多态法可实现对噪声系数小于0.2dB的极高灵敏度微波器件及设备进行高精度噪温测试，不确定度小于±1K。