射电天文研究室知识库

南山25米射电望远镜经过一年多的升级改造现已全面完成,主反射面直径增加至26米,为保证Q波段(30—50GHz)接收机工作效率,望远镜的表面精度需达到较高的水平,微波全息法可对天线面形进行精确测量和调整,是望远镜面形首次和定期精调的首选,为此我们基于新南山26米天线建立了一套全息法测量系统。整个系统包括参考天线、接收机、相关机、传输链路、时频参考、扫描控制和全息法处理软件等几部分,采用了带通采样技术直接对中频信号进行采集,减少了基带信号转换环节;采用高性能外部本振并利用氢钟输出的参考信号进行锁相,达到了极高的相位稳定度。目前整个系统已通过测试并取得了初步的测量结果,经处理分析,该系统工作正常,已达应用要求。

The upgrade work of Nanshan 25m telescope has been completed after more than one year with great efforts. The diameter of main reflector is increased to 26 meter. And to ensure the high observational efficiency of Q band receiver, we have to measure and adjustment the antenna penal elaborately. Microwave holography is the first choice for initial and periodical measurement of antenna surface due to the high precision of this method. So we build a holography system based on the new 26m antenna, which includes reference antenna, receiver, correlator, transmission link, time and frequency reference, antenna control software and holographic processing software. Some techniques have been used for simplify the hardware and promote the performance of this system. We use band pass sampling theorem for IF signal direct digitization, which can save the hardware device of baseband converter and decrease the phase fluctuation due to microwave signal mixing, filtering and amplification. To get a better phase stability of the system, we use a high performance Phase-locked Dielectric Resonator Oscillator (PDRO) for satellite signal mixing, which can support a very stable phase by lock the 10MHz reference signal from a hydrogen mazer. All parts of this system have been designed and tested, the result shows that the whole system works very well and meets the needs of application.