Abstract
This letter presents numerical results with a focus on power transfer
between two antenna arrays placed in the near field, where a much
smaller active multi-antenna feeder (AMAF) center feeds a far larger
passive array referred to as a reflective intelligent surface (RIS). The
AMAF is configured along the principal eigenmode of the AMAF-RIS
propagation matrix T. The interest is in the regime of f/D less than
unity. The power transfer coefficient deviates from the classical
distance dependent inverse square law model. This is due to the natural
taper across the RIS aperture at such small f/D ratios. In addition, the
behavior of the power transfer coefficient is more sensitive to the f/D
ratio than to a specific RIS size. We also see that the center feed is
more power efficient than end feed.