测地VLBI射频直接采样及射频数据处理方法的研究

传统的VLBI数据采集系统是把中频信号转换为数字基带信号。射频信号需要经历多级模拟器件才能转换为中频信号。这些模拟器件易受温度影响，产生系统群时延抖动。射频直接采样技术直接采样低噪声放大器输出的射频信号，利用FPGA的高速、并行数字信号处理能力，替代传统的模拟混频、模拟滤波，从根本上降低由模拟器件引起的系统群时延抖动。本课题拟结合电子技术和天文技术的方法理论，研究宽带接收机的射频数据处理方法、窄带接收机的射频数据处理方法和射频直接采样的VLBI数据格式器封装等。本课题拟在VADATECH天文数据采集平台上实现测地VLBI射频直接采样数据采集系统，应对VLBI数据采集系统的高稳定性、高可靠性、高测量精度的需求。课题的开展将提升我国VLBI数据采集系统的性能，加速我国VLBI在射频直接采样领域的发展。

The traditional VLBI data acquisition system converts the IF(Intermediate Frequency) signal to digital baseband signal. RF(Radio Frequency) signal needs to go through multi-stage analog devices before it can be converted into an intermediate frequency signal. These analog devices are susceptible to temperature, which will cause system group delay jitter. RF direct sampling technology directly samples the RF signal output by the low-noise amplifier, and replaces traditional analog mixing and analog filtering by FPGA which owns high-speed and parallel digital signal processing capabilities, which fundamentally reduces the system group delay jitter caused by analog devices. This project intends to combine the theories of electronic technology and astronomical technology to study the radio frequency data processing methods of broadband receivers, the radio frequency data processing methods of narrowband receivers, and the VLBI data formatter package of direct radio frequency sampling. This project intends to implement a geodetic VLBI radio frequency direct sampling data acquisition system on the VADATECH astronomical data acquisition platform to meet the requirements of high stability, high reliability and high measurement accuracy of the VLBI data acquisition system. The development of this project will improve the performance of VLBI data acquisition system in China, and accelerate the development of VLBI in the field of direct radio frequency sampling in China.