A Backend System for Accurate and Directional Measurements of Radiated EMI (Electromagnetic Interference) using Adaptive Cancellation Technique for Nullifying the Effects of Nearby Sources of Disturbance

摘要

Electromagnetic Interference (EMI) is a serious concern for space systems. This paper describes the backend system developed for the accurate measurements of the radiated EMI from any spacecraft subsystem or ground equipment. For accurate measurements of RF spectrum of any equipment, it is necessary to nullify the effect of nearby equipment. For this purpose, two antenna chains are received at the backend system. One chain will be from the main antenna and another from the reference antenna. Main antenna will be a highly directional antenna and reference antenna will be a near Omni-directional antenna. Backend system acquires data from these chains and run the adaptive subtraction algorithm which removes the unwanted (interference) signals coming from nearby sources and retains only the data from the required source. This algorithm is a refined technique which removes only the interference, leaving the underlying signal intact. After adaptive subtraction, FFT of the purified signal is taken to convert the signals into frequency domain. Further squaring of the frequency domain output provides the power spectrum of the signal. Alternatively, FFT can be run first and adaptive subtraction can be performed in frequency domain. This backend is developed using AD7026 microcontroller. Function generator was used to simulate the output of antenna chains. Experimental results along with MATLAB simulation results are presented in the paper. Furthermore, algorithm presented here can have wide range of applications in audio processing, radio receiver systems, radio astronomy etc.