  This paper studies the receiver to transmitter antenna coupling in near-field
communications with massive arrays. Although most works in the literature
consider that it is negligible and approximate it by zero, there is no rigorous
analysis on its relevance for practical systems. In this work, we leverage
multiport communication theory to obtain conditions for the aforementioned
approximation to be valid in MISO and SIMO systems. These conditions are then
particularized for arrays with fixed inter-element spacing and arrays with
fixed size.
