Early Time Behavior in Reverberation Chambers and Its Effect on the Relationships Between Coherence Bandwidth, Chamber Decay Time, RMS Delay Spread, and the Chamber Buildup Time
Reverberation chambers are emerging as a test facility for testing wireless devices and for emulating different wireless multipath environments. The commonly used quantities for characterizing the chambers in wireless applications are 1) the chamber quality factor, 2) the chamber decay time (τRC), 3) the RMS delay spread of the time-domain chamber response τrm s, and 4) the coherence bandwidth BW of the frequency-domain transfer function of the chamber. Analytic expressions that relate τRC and BW and the relationship between τrms and BW are given in the literature. However, these expressions neglect the early-time behavior of the chamber (the time before a chamber reaches a reverberant condition), and hence can give inconsistent results when one is analyzing experimental data. In this paper, we discuss the relationship between BW, τRC, and τrms for realistic chamber behaviors, and we present expressions for these relationships when one takes into account the early-time behavior of the reverberation chamber. This early-time behavior is crucial when one tries to assess and compare these different quantities in experimental data, and as we will see, the relationship between these quantities can be different for different chambers (i.e., different chamber sizes and loading conditions). The model presented here illustrates how the early-time behavior can affect these chamber characteristic quantities for loaded and unloaded chambers, and it also illustrates the problems that can occur when the early-time behavior is not considered.