A Complete System of Wireless Power Transfer Using a Circularly Polarized Retrodirective Array

A complete system of wireless power transfer using a circularly polarized retrodirective array is presented. A dual frequency, active retrodirective array is proposed for a transmitter system. The antenna array uses circularly polarized microstrip patch antenna subarrays with sequential rotation and surface wave suppression. The designed antenna element eliminates undesired coupling between array elements due to surface waves present in conventional microstrip antenna arrays in order to improve array performance. A sequential rotation technique was implemented to improve impedance matching and circular polarization bandwidths. The proposed retrodirective array was designed to operate at about 2.4 GHz for the interrogating signal and about 5.8 GHz for the retransmitted signal. The beam scanning inherent in retrodirective arrays ensures a uniform power level available to the receiving devices, regardless of their location within the angular sector over which retrodirectivity is achieved. A rectenna was designed as a receiver in order to have a complete system the wireless power transfer. A zero bias Schottky diode with high detection sensitivity was used as the rectifying device. The shorting pins used in the antennas to suppress surface waves also act as return paths for the DC current, eliminating the need for an RF chock in the rectifier circuit. The design procedure, simulation results, and experimental measurements are presented.