High gain antennas in a random environment

The scattering environment encountered in mobile and personal communications is usually not considered as a practical background for directive antennas. However, when using adaptive antennas such as antenna arrays at each end of the link it is possible on average to achieve array gains almost as high as in free space. This presupposes a known channel at both ends which is a possibility with time-division-duplex systems and terminals which are quasi-stationary. The paper gives the theoretical background for such arrays.