by the number of modes per megahertz). This is, to a good approximation, given by the classical formula (12.10) © 2009 by Taylor & Francis Group, LLC Measuring Performance of 3GPP LTE Terminals The number of independent samples is proportional to the mode density, but the proportionality constant is not known because it depends on chamber load- ing, mode stirring methods, mechanical stirrer shapes, and the shape of the cham- ber. A preliminary experimental study has been performed [22], but more work is required to get unique and simple conclusions. However, we can preliminarily state the following relation between the mode density and the number of independent samples: (12.11) where B is the bandwidth of the frequency stirring. The factor 8 is due to plat- form stirring and is based on empirical experience as well as physical reasoning. It is clear from Equations (12.9) and (12.11) that the accuracy in a given chamber can be controlled by Af and B. However, it should be noted that other effects are coming in when the loading is very large, SO some care must be taken. Still, we have experienced a good Rayleigh distribution with many independent samples in a heavily loaded chamber with Q as low as 30 [23]. The problem with frequency stirring B is that the frequency resolution becomes worse. For antenna measure- ments, this means that we cannot resolve variations in the radiation efficiency that are faster than B. In practice, the resolution is somewhat better by using the mis- match-corrected chamber transfer function (12.8) before power averaging because mismatch efficiencies normally vary more quickly with frequency than efficiencies due to ohmic losses. 12.2.4 Research Activities on Reverberation Chambers The reverberation chamber has been used for more than 20 years for EMC mea- surements like electromagnetic susceptibility and emissions, as described in the overview article by Bäckström, Lundén, and Kildal [7]. Its basic theories are well understood due to several papers by D. Hill at the National Institute o