Noise Analysis of EPR Spectrometers with Cryogenic Microwave Preamplifiers
Noise Analysis of EPR Spectrometers with Cryogenic Microwave Preamplifiers
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带低温微波前置放大器的 EPR 光谱仪的噪声分析
DOI：
10.1006/jmra.1995.1052
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发表时间：
1995
期刊：
影响因子：
--
通讯作者：
J. Hyde
中科院分区：
文献类型：
--
作者：
S. Pfenninger;W. Froncisz;J. Hyde
本文报道了利用低温致冷器（噪声系数为0.5dB，等效噪声温度为35K）的EPR谱仪的灵敏度研究。考虑三种情况：（a）在CW实验中匹配的谐振器，（B）被过耦合破坏的谐振器Q，以及（c）在脉冲实验中匹配的谐振器。由于微波电桥中的损耗对系统噪声的贡献已经被定量地确定：接收机链的等效噪声温度从35 K上升到100 K。有人建议，可以通过冷却微波桥的主要部件来实现改善的系统性能。在环行器的端口1处冷却负载电阻器是特别有利的。源噪声的测量报告。随着系统噪声的降低，这种噪声贡献变得越来越明显，但可以通过使用环隙谐振器来抑制。分析是在一个混合的工程词汇的输出噪声温度和等效噪声温度，这是指的输出和输入的电路，分别温度。有人建议，这是一个适当的分析方法时，有多个路径，饲料噪声的输出电路与不同的物理温度的输入负载电阻为每个路径。
Abstract Studies are reported on the sensitivity of an EPR spectrometer utilizing a cryogenic preamplifier (0.5 dB noise figure, 35 K equivalent noise temperature). Three cases are considered: (a) resonator matched in a CW experiment, (b) resonator Q spoiled by overcoupling, and (c) resonator matched in pulse experiments. Contributions to the system noise because of losses in the microwave bridge have been determined quantitatively: the equivalent noise temperature of the receiver chain rises from 35 to 100 K. It is suggested that improved system performance can be achieved by cooling major components of the microwave bridge. It is particularly advantageous to cool the load resistor at port 1 of the circulator. Measurements of source noise are reported. This noise contribution becomes increasingly apparent as the system noise is decreased, but can be suppressed by use of loop-gap resonators. Analysis is carried out in a mixed engineering vocabulary of output noise temperature and equivalent noise temperature, which are temperatures referred to the output and input of the circuit, respectively. It is suggested that this is an appropriate analytical approach when there are multiple paths that feed noise to the output of the circuit with different physical temperatures of the input load resistor for each path.