  In this paper we propose an extended LOS MIMO channel model, which considers
an additional phase shifting term in the transmission path, and which provides
the potential to improve channel conditioning significantly. We show that this
phase shifting can, for example, be achieved by adding a dielectric material
between the transmitting and receiving antennas, where the phase shift is
dependent on the distance the waves travel in the medium. Using that distance
as a design parameter we demonstrate that the optimal spacing between antenna
elements of uniform linear arrays, achieving full spatial multiplexing, can be
reduced compared with the well-known spacing criterion from previous
investigations.
