edback of whether or not there has been improvement. In a few years, it will be hard to imagine designing diversity antennas any other way. Companies with reverberation chambers almost always use this method only when designing or evaluating diversity gain. © 2009 by Taylor & Francis Group, LLC Long Term Evolution: 3GPP LTE Radio and Cellular Technology 12.3.6 Measuring MIMO Capacity A necessary condition for MIMO antennas to provide higher throughput is that the antennas be relatively uncorrelated-the more so, the better. The communication must also take place in a fading environment, so that the different propagation paths are relatively uncorrelated. The more fading that occurs, the better. Furthermore, the most important parameter for good MIMO performance is that the antennas used have high antenna efficiency [29]. We saw in the preceding diversity case that the antenna efficiency is decreased when antennas are in close proximity. In the reverberation chamber, it is possible to measure what the propagation paths in a Rayleigh fading environment look like between the MIMO antennas and the three fixed wall antennas (i.e., the channel matrix H). If the matrix is known, it is pos- sible to calculate the throughput capacity with Shannon's capacity formula: C log 2(det (IM + (SNR/3)H*)) (12.25) With a multiport network analyzer, such a measurement can be performed in only 1 minute in the Bluetest high-performance chamber. It is the same measure- ment as described in the section on diversity gain, but the postprocessing of the S parameters is different. If one does not have a multiport network analyzer or if the MIMO antenna consists of more antenna branches than one has ports, fast MIMO measurements can still be taken by measuring the MIMO channel columns of the H matrix one by one. Figure 12.10 shows an example of a MIMO antenna with six branches. In this case, one starts by connecting one of the antenna ports of the test antenna to the network analyzer and the other ports and the reference antenna are Switch Net