In-situ frequency calibration of frequency modulated continuous wave reflectometry.
In-situ frequency calibration of frequency modulated continuous wave reflectometry.
复制标题
DOI：
10.1063/1.5038829
复制
发表时间：
2018-10
期刊：
影响因子：
--
通讯作者：
S. Seo
中科院分区：
文献类型：
--
作者：
S. Seo
调频连续波反射计已用于测量KSTAR托卡马克等离子体密度剖面。三个反射计在Q波段（33-50 GHz）、V波段（50-75 GHz）和W波段（75-110 GHz）的频率范围内工作在非常偏振模式下。每个全频带在20 μs内线性扫描。密度分布测量的精度取决于频率校准的精确程度。提出了两种新的频率测量技术，用于在20 μs扫描时间内现场标定瞬时频率。首先，基于小波变换分析接收机的中频（IF），将来自频率合成器的固定频率信号施加到本振（LO）端口。通过将测量的IF与给定的LO频率相加或相减，可以简单地获得发射微波的频率。一旦知道了整个系统的群延迟，就可以通过测量IF来校准频率。利用不同长度的延迟线测量无等离子体时的反射计输出，并将其相减，通过消除除延迟线的已知群延迟外的系统的未知群延迟，就可以校准频率。这两种技术进行了详细的描述，并进行了比较，由这两种技术的校准频率。
Frequency modulated continuous wave reflectometers have been used to measure the plasma density profiles of the KSTAR tokamak. Three reflectometers are operating in an extraordinary polarization mode in the frequency range of Q band (33-50 GHz), V band (50-75 GHz), and W band (75-110 GHz). Each full frequency band is linearly swept in 20 μs. The accuracy of the density profile measurement is dependent on how precisely the frequency is calibrated. Two new frequency measurement techniques are developed to in situ calibrate the instantaneous frequency during the sweep time of 20 μs. First the intermediate frequency (IF) of the receiver is analyzed based on wavelet transform as applying a fixed frequency signal from a synthesizer to the local oscillator (LO) port. The frequency of the transmitted microwave is simply obtained by adding or subtracting the measured IF to the given LO frequency. Once the group delay of the whole system is known, the frequency can be calibrated by measuring the IF. By measuring the reflectometer output without plasma with delay lines of different lengths and subtracting them, the frequency can be calibrated by eliminating the unknown group delay of the system except the known group delay of the delay line. These two techniques are described in detail, and the calibrated frequencies conducted by the two techniques are compared.