Electromagnetic reverberation chamber EVA

Mode-stirred chamber EVA

The so-called mode-stirred chamber (MSC or RC, which stands for "reverberation chamber") is according to the normative standards ECSS-E-ST-20-07C and MIL-STD-451G approved as an alternative tool for interference immunity testing (EMS testing) of electronic component. As with the absorber chamber, a mode-stirred chamber shields the test object from the omnipresent EM fields and waves in the environment. In contrast to the absorber chamber, however, the mode-stirred chamber does not represent an ideal replication of free space. In addition to shielding against EM radiation from the environment, multiple reflections by the metallic walls of the chamber lead to the formation of standing waves with a discrete frequency spectrum which differs from free-space spectrum. This affects the emission from the test object in case of EMI measurements as well as that of the transmitter in case of EMS measurements. To overcome this issue and to realize a quasi-continuous frequency response in the measurements, the mode spectrum is tuned by a periodic change of the boundary conditions for the standing waves. For this purpose, an asymmetrical, movable mode stirring element is used, which deflects the waves in different directions of propagation.

One advantage of such a mode-stirred chamber is that significantly higher EM field strengths can be generated in EMI measurements compared to the absorber chamber at the same amplifier power. Since no absorbers are required, this test room can be built in a very compact way. In addition, the chamber is also the vacuum tank to create the space conditions required for operating a thruster. This test setup can, therefore, be implemented in a cost-effective manner. However, in contrast to the absorber chamber, no angle-resolved radiation characteristics can be measured in a mode-stirred chamber; only integral measurements are possible.

According to the normative, only interference immunity measurements (EMS testing) are permitted with a mode-stirred chamber. The aim of the JLU space laboratory is to also use this chamber to determine the integral emission characteristics (EMI) of the test objects. Although this EMI test may not be used as a validation of normative standards, it offers valuable input for the development thrusters. It may serve as preliminary test prior to actual EMI testing in a semi-anechoic chamber.

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