Design of planar antenna array for the generation of near-distance energy hotspots

The theoretical beam efficiency in the far-field, as calculated by the Friis transmission equation, exhibits a considerable decrease within a few wavelengths from the radiating element. Consequently, applications like wireless power transfer and imaging are limited at large distances due to the low efficiency of the beam. To address this challenge, the use of radiating near-fields has been proposed. This work integrates the concept of a phased array antenna on an X-shaped array of patches to generate a desired focal region. The primary aim of this work is to engineer the energy hotspot at a distance well beyond the near-field region of the constituent patch antenna while also encompassing large dimensions in terms of range and cross-range, thereby relaxing the geometrical constraints typically associated with wireless power transfer operations. A frequency-scaled prototype of an 8-element patch array and an isolated element operating at 2.25 GHz has been fabricated and measured, verifying the proposed working principle.