Including Antenna Effects Into Capacity Formulations of Line-of-Sight MIMO Channels

Analytical expressions for the capacity of multiple-input multiple-output (MIMO) line-of-sight (LOS) channels that include antenna effects in both the near- and far-field regions are provided. They extend previous formulations for LOS capacity in that they provide insights into capacity results across the full range of antenna element separations. This range includes element separations tending to zero, and more generally, we show that MIMO LOS capacity at antenna element separations of less than five wavelengths differs from previous results without antenna effects. In addition, the results reveal an optimum antenna element separation to maximize the capacity for single-rank MIMO LOS channels. A novelty of the approach is that all results are obtained with analytical expressions and can thus be easily incorporated into system formulations. The results have applications in MIMO LOS channels, including those involving unmanned aerial vehicles (UAVs) and wireless communication systems in millimetre-wave and terahertz bands.