two spatial channels for EPD-S2 communication; consequently, two spatial channels are available for D-S communication Fig. 2.14 Proof of concept: a number of scatting wire antennas closed on electronically controllable loads are placed around a transmitting MIMO antenna; the loads of the elements are selected in order to optimize the channel capacity of the MIMO system [77] Further information can be obtained by the analysis of results obtained by ADAM antenna [77], a prototype built in 2006. ADAM consists of a standard MIMO antenna with two radiating elements surrounded by a 6 bits EPD made using wire antennas closed on electronically controllable loads (Fig. 2.14). In this way we have a controllable scattering environment around the antenna. ADAM was tested in a 2 X 2 MIMO communication system working at 2.5 GHz (center frequency) transmitting 30 tones with 1 MHz spacing [78]. The results were compared with the results obtained using the same communication system in the same environment but without the EPD. The singular values in case of absence of EPD are plotted in Fig. 2.15 as blue circles. The figure shows that only 30 singular values associated with the 30 tones of the first spatial subchannel are relevant, while the remaining are below -20 dB. The use of EPD gives the singular value distribution drawn in the same figure as blue circles. The singular values are normalized to the first singular value in absence of EPD to simplify the comparison. The figure shows an increase of the amplitude of all the singular values. In particular, in presence of modest SNR ratio, it is possible to obtain many more space-time channels. For example, with a SNR of 15 dB, it is M. D. Migliore Fig. 2.15 Example of singular values without (blue circle) and with (red stars) control of the environment; the optimization of the scattering environment doubles the STNDF available for the transmission possible to have more than 50 space-time channels, while a SNR of 20 dB allows the use of all the available space-time channels. The in