Multi-User Near-Field Focusing Through Time-Modulated Arrays

The feasibility of a novel near-field (NF) focusing technique based on time-modulated arrays (TMAs) is studied. The formulation for an NF transmission problem is developed, showing its interesting potential for multiuser focusing at different frequencies, advantageously exploiting the characteristic TMA side frequencies radiation. Although asking for specific patterns at a set of different radiation frequencies may degrade the overall system performance, it is shown that the required radiated field distributions may still be achieved with acceptable focusing performance. This fact makes TMAs an interesting alternative to other technologies due to their simpler implementation through digital devices and also allowing for an adaptive implementation as required for many real applications. Some illustrative examples are presented.