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

我们研制了一种小型偶极子天线系统，该系统将安装在航天器上，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难点是如何降低航天器上电气设备的电磁噪声干扰，为此，我们研制了一种基于数字信号处理器（DSP）的实时噪声抑制信号处理器，其中采用了“中值滤波法”。我们对GEOTAIL、AKEBONO和NOZOMI卫星的各种电磁噪声进行了检测，得到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。利用这种特性差，我们在DSP上实现了软件，可以有效地抑制周期性仪器噪声。在这种新的滤波技术中，等离子体波的波形没有变形。小尺寸天线可以沿卫星自转轴方向安装，使我们可以同时测量等离子体波的三维波矢量。

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.