SMALL-SIZE ANTENNA SYSTEM FOR PLASMA WAVE MEASUREMENTS ONBOARD SPACECRAFT USING EM INTERERENCE NOISE REJECTION

我们研制了一个小型的偶极子天线系统，安装在航天器上，用于测量行星磁层和行星际空间的等离子体波。设计这种天线系统的主要困难是如何降低来自航天器上电气设备的干扰电磁噪声，我们利用数字信号处理器（DSP）研制了一种实时抑制噪声的信号处理器，其中采用了“中值滤波法”。我们已经检查了来自GEOTAIL，AKEBONO和NOZOMI卫星的各种电磁噪声，并获得了它们之间的一些共同特征，以及与天然等离子体波的特征差异。使用这样的特性差异，我们已经实现了DSP上的软件，大大抑制了周期性的仪器噪声。在这种新的滤波技术中，等离子体波的波形没有变形。这种小型天线可沿着卫星自旋轴安装，使我们能同时测量等离子体波的三维波矢。

We have developed a small-size dipole antenna system which to be installed onboard spacecraft to measure the plasma waves in the planetary magnetosphere and inter-planetary space. Main difficulty in designing such antenna system is how to reduce the interference electromagnetic noises from the electrical equipment onboard spacecraft, and we have developed a signal processor for real-time noise rejection using the digital signal processor (DSP), in which we used the "median filtering method". We have examined various electromagnetic noise from GEOTAIL, AKEBONO and NOZOMI satellites and obtained some common features among them, and characteristic differences from the natural plasma waves. Using such a characteristic difference we have implemented software on the DSP to suppress considerably the periodic instrumental noises. In this new filtering technique, there is no deformation in the waveform of the plasma wave. The small-size antenna can be installed along the satellite spin axis, which will make us to measure simultaneously three dimensional wave vectors of plasma waves.