射电天文毫米波接收机强度校准

The Amplitude Calibration of Radio Astronomy Millimeter Wave Receiver

射电天文强度校准的目的是将接收设备对天文观测源的响应转换为天文意义上的流量.在常用的射电天文强度校准方法中,厘米波校准主要使用噪声注入模式,就是将1个标准噪声信号在馈源和极化器之后注入到接收机内部进行校准.由于毫米波微波器件的小型化导致噪声注入模式不易实现,加之注入模式可能引入噪声,因此BTL (Bell Telephone Laboratory)最早提出使用斩波轮技术进行毫米波校准,就是在馈源口面交替放置或者移除常温黑体进行校准;之后BIMA (Berkeley Illinois Maryland Association Array)又提出使用常温、热负载进行校准; ALMA (Atacama Large Millimeter Array)对单、双负载校准方式的精度进行计算后,认为双温度负载校准方式有潜力实现1%的校准精度,并最终设计出机械臂式双温度负载校准机构;此后, GBT (Green Bank Telescope) 4 mm波段制冷接收机设计出旋转盘式双温度校准机构; OSO (Onsala Space Observatory)最新研制的3 mm波段制冷接收机设计出波束切换式双温度校准机构.中国科学院新疆天文台QTT(Qi Tai Telescope)项目的启动推动了毫米波接收机研制进程,为提高毫米波强度校准精度,相关的技术预研已经开始.

The purpose of radio astronomical amplitude calibration is to convert the response of the receiving equipment to flux density for radio sources.In usual methods of radio astronomical amplitude calibration,the centimeter wave calibration mainly uses noise injection mode,which is to inject a standard noise signal into the receiver after the feed and polarizer to calibrate inside.Due to the miniaturization of millimeter wave microwave devices,the mode of noise injection is not easy to be realized,and the injection mode may introduce noise.So BTL(Bell Telephone Laboratory)first proposed to use the chopper wheel technique for millimeter wave calibration,which is to alternately place or remove the room temperature blackbody on top of the feed of receiver for calibration.Then BIMA(Berkeley Illinois Maryland Association Array)also proposed to use room temperature and thermal load to calibrate;ALMA(Atacama Large Millimeter Array)calculated the accuracy of one or two load calibration methods,and it is considered that the two load calibration method has the potential to realize the calibration accuracy of 1%,and finally it designs the mechanical arm type calibration mechanism with two temperature load;after that,the GBT(Green Bank Telescope)4 mm band cryogenic receiver designs rotary table of calibration mechanism with two temperature load;the latest development of 3 mm band cryogenic receiver from OSO(Onsala Space Observatory)designs the beam switching of calibration mechanism with two temperature load.The QTT(Qi Tai Telescope)project of the Xinjiang Astronomical Observatory of Chinese Academy of Sciences has promoted the development process of millimeter wave receiver.In order to improve the amplitude calibration accuracy of millimeter wave,the related pre-research has begun.