Implementation of a reverberation chamber for electro-magnetic compatibility measurements

Abstract

This research project focuses on the implementation of a Reverberation Chamber (RC) by the transformation of an existing electromagnetically shielded room. The reverberation chamber is a kind of shielded room designed to create a statistically random internal electromagnetic environment. The reverberating environment makes it possible to obtain high field strengths from a relatively low input power. The electric fields in the chamber have to be stirred to achieve a statistically uniform field. The first part of this thesis presents an overview of reverberation chamber principles and preliminary calculations are done: the lowest usable frequency is estimated to be close to 300 MHz from empirical criteria. Modelling of the statistical environment is then presented, where electromagnetic quantities are characterised by probability density functions (Gaussian, Rayleigh and exponential); correlation issues are also presented. Measurements are performed in the frequency range of 800 MHz – 4 GHz, dictated by the antennas available for this research study. An investigation of cable losses is conducted, followed by a discussion on measurement accuracy. Mechanical stirrers are designed and manufactured. Electromechanical components are selected based on the literature study. Measurements are obtained through an automated setup using MATLAB®. To verify that the RC, with its in-house designed mechanical stirrers, is well-operated, the stirring ratio is experimentally determined. After this first test, an exhaustive investigation of probability density functions is conducted, taking into account correlation issues. Measurements show that the quality factor of the chamber is close to 2000 at 3 GHz, and that 60 independent stirrer positions at 4 GHz can be used for statistical analyses. Finally, the uniformity test is performed with an improved accuracy using frequency stirring. In conclusion, the CPUT RC passes the validation procedure according to the IEC 61000-4-21 standard by generating the required field uniformity within the accepted uncertainty level.