This paper addresses the spatial-wideband effect in line-of-sight multiple-input multiple-output channels. This effect arises once the bandwidth is large enough that the differences in propagation delays for distinct transmit-receive antenna pairs cease to be negligible relative to the symbol period; this, in turn, gives rise to intersymbol interference. The impact of this effect is quantified as a function of the relevant geometric parameters (range, array orientations, antenna spacings) and a family of scalable solutions is proposed to counter it. In particular, a solution based on per-antenna delay lines at transmitter and receiver is shown to be highly effective, and a criterion is derived to set those delay lines as a function of the channel.

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