Efficiency Analysis of Innovative Tuning Methods for Immunity Testing in Reverberation Chamber and Comparison to Anechoic Room. Application to Civil and Military Testing in the RMA Chamber

摘要

Starting from the theory of resonances of time harmonic fields in resonating cavities, based on the Helmholtz equation, we have presented the principle of operation of the Reverberation Chamber (RC): a n electrically large cavity where the resonant frequencies are changed with a tunerin order to obtain a uniform maximum electric field, within a time cycle. This type of test facility can be used as an alternative to the conventional Semi-Anechoic Room (SAR) for testing the immunity of electronic equipment to high intensity radiofrequency fields. But, at the opposite of the deterministic environment present in a SAR, the RC generates electromagnetic waves with a direction of incidence, a polarization and a time of arrival on the Equipment Under Test (EUT) that are varying randomly in time. The presented research had two objectives: the firstis to conceive, design and evaluate the efficiency of innovative and less cumbersome tuning systems and the second is to compare the severity level of RC and SAR for immunity testing by using both facilities available at Royal Military Academy (RMA). The first innovative tuning method (RAIL) we have conceived, designed and assessed in the RC at RMA is a dynamic source-mode tuning based on a translation movement of two broadband antennas on two orthogonal rails. The efficiency analysis shows that it complies with the field uniformity requirement ofthe IEC 61000-4-21. The second innovative tuning method (STATIC) we have conceived and investigated in the same RC is based on a fixed network of sixteen static antennas where a limited subset of eight antennas is randomly activated by means of fast electronic switches. Tuning is obtained without any movement in the RC. The technological breakthrough is that important testing time reduction can be achievedwhen using the STATIC tuner instead of using conventional mechanical tuners. Using the RAIL tuner, we develop a new method for measuring the radiation efficiency of an antenna in a RC without the need of a reference antenna. In order to perform a severity comparison of the immunity testing to Electric fields between a SAR and a RC, a Canonical Equipment Under Test (CEUT) has been designed, developed and manufactured at the RMA. It is an original realization with no equivalent in the EMC community. An unexpected development of this initiative lies in the fact that it has been accepted as reference material for interlaboratory testing in the field of radiated immunitytesting to RF, according to IEC 61000-4-3. Moreover, EMC testing laboratories in Germany and Japan have shown interest and have participated inthis campaign. The comparison of radiatedimmunity testing performed both in a SAR and a RC has produced several interesting results. Applied to test RS103 of the MIL-STD-461F, it meansthat with one aspect angle in a SAR, it is recommended to use from 20 to 30 tuner steps, in a RC, in order to achieve equivalence of testing results. For the IEC 61000-4-3, testing with 4 aspect angles in a SAR willneed from 40 to 60 tuner steps for equivalence. Finally, we have shown experimentally that, in a RC, spatial averages and time averages are equal; this is a characteristic of ergodic processes. This experimental demonstration of ergodicity establishes a scientific breakthrough since, as far as we know, there is no literature about this subject yet. From now on, we can say that the stochastic generation of an electric field in a RC is a stationary process and that various statistical parameters in its volume can be estimatedby measuring the time average in a fixed spatial point.