9.1 Introduction

In the previous chapters receiver diversity related to antenna arrays has been discussed to some extent, but the additional flexibility derived from having more than one antenna element leads to many more uses, some of which are rather recent and which only have attracted theoretical attention. The interdependence between the antennas and the propagation environment is even more clear in this new connection, since the signal correlation between elements is very important for the potential applications, and this correlation depends on the angular spread as seen from each array antenna, as has been shown in Section 6.4. The situation may be described as given in Figure 9.1.1.

Figure 9.1.1: Two antenna arrays in a scattering environment. The angular spread seen from the two arrays may be different. The antennas to the left see a small angular spread and those on the right see a large spread even though the modelled scatterers (marked *) are common. The situation is characteristic of a macrocellular environment with the base station to the left and the mobile to the right

In general there will be M transmitting antennas in a transmit array and N receiving antennas in a receive array. Although there will be reciprocity between any two antennas, it will be necessary to distinguish between the transmit and receive situation, since the knowledge of the channel parameters may be different in the two situations. Also in the most general case the angular spread of the...