Electrically Small CP Unidirectional WPT and Comm Antennas for Amalgamation into a Retrodirective Reconfigurable Intelligent Surface (RRIS) System

This paper presents a circularly polarized wireless power transfer (WPT) and communication antenna system for amalgamation into a retrodirective reconfigurable intelligent surface (RRIS) system. The combination of these two subsystems facilitates tracking the direction of an IoT object and wirelessly powering it. The WPT and Comm functions associated with the IoT device itself are enabled by the developed dual CP rectenna/antenna system. The communication portion of the antenna system sends a pilot signal to the RRIS if it requires power. The RRIS uses the field of this received pilot signal to determine the direction of the IoT device needing power and will then transform itself from a RIS into a retrodirective array that transmits a time-reversed EM field to it. The WPT portion of the antenna then receives the EM field backpropagated to it and efficiently converts the received AC signal into DC power. The dual CP antenna system consists of two crossed electrically small Egyptian axe dipoles (EADs), two crossed capacitively loaded loops (CLLs), and a delayed loop feeding structure. RHCP (LHCP) Huygens radiation patterns are realized by one (the other) of two orthogonal excitations of the same radiator. Good isolation is observed (< –15 dB) between its transmitting and receiving ports. The dual CP rectenna/antenna system is designed to operate at 915 MHz in the free industrial, scientific and medical (ISM) band.