Multiple-Active Multiple-Passive Antenna Systems and Applications

This chapter focuses on extensions and foreseen applications of the parasitic antenna array technology. Moving beyond the single-active (single-RF) communication setup, hitherto discussed in the previous chapters, the work in this chapter extends the analysis to generalized multiple-active multiple-passive (MAMP) antenna topologies, as explained in Sect. 8.1. Then, Sect. 8.2 proposes MAMP antenna structures with application to reconfigurable MIMO transmission in the presence of antenna mutual coupling under poor scattering channel conditions. For this purpose, the section presents an adaptive MAMP antenna system capable of changing its transmission parameters via passive radiators attached to tunable loads, according to the structure of the RF propagation channel. The hybrid MAMP array structure can be tractably analyzed using the active element response vector (instead of the classical steering vector) and the active element current vector (all being functions of the variable loading). The adaptive MAMP system targets at maximizing tight MIMO ergodic and outage rate bounds, relying on partial channel knowledge when tuning to a different loading state for optimizing the rate of communication. The proposed adaptive MAMP system can be limited to practical dimensions whereas the passive antennas require no extra RF hardware, thus meeting the cost, space, and power constrains of the users’ mobile terminals. The simulation results show that the adaptive MAMP system, thanks to its “adaptivity”, is able to achieve satisfactory performance even in poor scattering environments whereas a significant part of the mutual information that is lost owing to the spatial correlation and the electromagnetic coupling is successfully retrieved. Section 8.3 extends our communication scenario to account for multiuser diversity systems, describing novel parasitic antenna-assisted switched beam array architectures for enhanced selection combining with application to the downlink of cellular systems exploiting multiuser diversity. Specifically, this section deals with the problem of the poor performance of antenna selection for compact user terminals in multiuser diversity systems. Although antenna selection is a simple and efficient technique for enhancing the downlink performance of multiuser diversity systems, the large antenna inter-element spacing required for achieving spatial diversity is prohibitive for user terminals due to size restrictions. In order to allay this problem, miniaturized switched-beam MAMP receiver designs assisted by low-cost passive reflectors are proposed. Unlike conventional spatial receive diversity systems, the proposed angular diversity architectures occupy a small volume, whereas the antenna system properties are optimized by controlling the strong reactive fields present at small dimensions. The systems are designed for maximum antenna efficiency and low inter-beam correlation, thus yielding K practically uncorrelated receive diversity branches. The simulation results show that the proposed enhanced diversity combining systems improve the average throughput of a multiuser network outperforming classical antenna selection especially for small user populations and compact user terminal size.