Measurements and analysis of antenna impedance aboard the Geotail spacecraft
Measurements and analysis of antenna impedance aboard the Geotail spacecraft
复制标题
Geotail 航天器上天线阻抗的测量和分析
DOI：
10.1029/97rs00396
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发表时间：
1997
期刊：
影响因子：
1.6
通讯作者：
T. Okada
中科院分区：
文献类型：
--
作者：
M. Tsutsui;I. Nagano;H. Kojima;K. Hashimoto;H. Matsumoto;S. Yagitani;T. Okada
一种实用的方法可以估计科学航天器 Geotail 上的电偶极子天线的有效阻抗。新提出的方法的原理是通过分析将校准信号直接施加到天线上时捕获的信号波形来导出浸没在空间等离子体中的偶极子天线的复阻抗。导出的复数天线阻抗表示为其实部和虚部的频率响应。 Geotail在地球磁层飞行期间，在磁层的各个区域进行了阻抗测量。通过对测量数据的分析证实，Geotail天线的阻抗形成了一个由电阻和电容并联组成的等效电路。研究发现，磁层中极其稀有的环境等离子体密度很容易改变电阻值。测量值的有效性已经根据鞘层区域中的探针理论进行了检验，同时考虑到由于天线表面的光电子发射而升高的天线电势。分析结果表明，天线电阻的测量值与理论计算得到的护套内电阻值一致。从测量和计算获得的电容值的相关图表明，测量的电容的主要部分代表“鞘层电容”，但除了自由空间电容之外，其他部分可能是由鞘层阻抗和等离子体阻抗的组合产生的。
A practical method of estimating the effective impedance of electric dipole antennas aboard the scientific spacecraft Geotail has been developed. The principle of the newly proposed method is to derive the complex impedance of the dipole antennas immersed in the space plasma by means of the analysis of signal waveforms captured when a calibration signal was imposed directly onto the antennas. The derived complex antenna impedance is expressed as frequency responses of its real and imaginary parts. During the flight of Geotail in the Earth's magnetosphere, the impedance measurements were conducted in various regions of the magnetosphere. It has been confirmed, from the analysis of the measured data, that the impedance of the Geotail antenna forms an equivalent electric circuit consisting of a resistance and a capacitance connected in parallel. It has been found that the resistance value is easily changed by the extremely rare ambient plasma density in the magnetosphere. The validity of the measured values have been examined along a theory of probes in a sheath region, taking into account antenna potentials which are lifted up due to the photoelectron emissions from the antenna surface. The analyzed result shows that the measured values of the antenna resistance are consistent with those within the sheath calculated from the theory. Correlation plots of the capacitance values obtained from both the measurements and the calculations have shown that the major parts of the measured capacitance represent the “sheath capacitance,” but other parts might result from a combination of the sheath impedance and the plasma impedance, in addition to the free‐space capacitance.