Characterizing Large-Form-Factor Devices in a Reverberation Chamber

With new technologies such as machine-to-machine communications there is a growing need to test large-form-factor devices in reverberation chambers. The performance of the reverberation chamber can be affected by the physical characteristics of these devices. In this report it is discussed how the spatial uniformity of the received stirred power and the received total power (stirred + unstirred power) are affected by a large object. A distinction is made between reflecting and absorbing objects. The chamber was loaded by stacking metallic boxes (cardboard boxes wrapped in aluminium foil), or by stacking RF absorbers. The metallic boxes slightly load the chamber. Measurements show that this is caused by the cardboard being lossy. The absorbers significantly load the chamber. It is shown that large metallic objects cause minimal degradation in the spatial uniformity. Absorbing objects can cause substantial degradation in the spatial uniformity, motivating the need for testing guidelines for these objects. The spatial uniformity with respect to the total received power degrades because the unstirred energy becomes more dominant for a loaded chamber. The unstirred components are the energy that is coupled from the transmitter to the receiver without interacting with the paddle. The stirred component is the energy that interacts with the paddle. If the unstirred components are removed, the spatial uniformity still degrades with increasing numbers of absorbers. A reason for this degradation is found in the proximity effect. The proximity effect is explained by the fact that an absorber in close proximity of an antenna appears to be larger, and is for this reason more likely to occupy a larger amount of the antenna pattern. The absorber does not reflect electromagnetic waves, so an antenna in close proximity of an absorber will receive less power. In future work, the effect of absorbers on the spatial uniformity of the stirred power will be further investigated. It is proposed to study the spatial uniformity in the chamber when it is corrected for the proximity effect. iii iv Summary Contents Summary iii 1 Introduction 1