Abstract

Air-core (donut-shaped) microwave beams are attractive for wireless power transfer (WPT) for drones because their central intensity null can reduce field concentration near mission equipment mounted near the drone center. This paper proposes a fixed air-core beam WPT architecture in which the transmitting beam is not electronically steered; instead, the drone maintains its position near an efficient receiving region using onboard control based on relative beam-position information inferred from received signals. To support this architecture, we present a theoretical analysis of captured power and spillover for a circular receiving aperture illuminated by a Laguerre–Gaussian (LG) beam. Rather than claiming a direct extension of the modified Friis formula to LG beams, we derive a closed-form expression corresponding to the edge-based efficiency/spillover interpretation used in Gaussian-beam WPT discussions. We then report staged experimental validation using a 24 GHz radial line slot antenna (RLSA)-based air-core beam transmitter with a 25 W class feed circuit, a horn-antenna-based reference receiver for principal validation, and a panel rectenna prototype for implementation-oriented evaluation. The results clarify practical operating conditions and implementation limitations, including distance-dependent position-detection behavior and compact-receiver sensitivity degradation under air-core beam illumination.

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