 by Hill [20,25,26]. 12.2.5 Benchmarking of Reverberation with Anechoic Chambers During the first years of development of the reverberation chamber into an accu- rate instrument for antenna and terminal measurements, it was found that the accuracy could be considerably improved by making use of new stirring methods, referred to as platform stirring [16] and polarization stirring [17]. Using these stir- ring methods, the radiation efficiency of small antennas and radiated power of mobile terminals could be measured with an accuracy of 0.5-dB RMS [27] in a small reverberation chamber. This was carefully validated by comparison with mea- surements in anechoic chambers [28] and larger reverberation [27]. More recently, several reverberation chambers of different sizes participated in a round-robin test within the framework of ACE (European Antenna Center of Excellence) [43]. The basic idea was to collect data from different test facilities around Europe for pas- sive as well as active test devices and to compare the results. The focus was on the most popular frequency bands typically used in mobile communications systems. In total, 12 organizations participated in the measurement campaign and 5 used reverberation chambers. In order to guarantee comparable results, only one test kit was sent around (see Figure 12.5). In order to define simple and repeatable test cases for the round robin, passive antennas consisting of half-wavelength dipoles for 900-, 1800-, and 2400-MHz bands and a slot antenna for the 5.2-GHz band were used. In order to account for losses in objects close to the terminal antenna (e.g., resembling the head of a mobile phone user), the test fixture consisted of a lossy cylinder and an adjustable antenna mount (Figure 12.5). The cylinder contains a lossy liquid and is sealed SO that all participants measure under the same conditions. The distance between the antenna and the cylinder can be adjusted, SO the radiation efficiency can be varied. The distance can accurately be read on a scale on the antenn