A Miniaturized Wearable Two-port Loop Rectenna for Energy Harvesting at millimeter wave

The design of a novel two-port loop antenna, operating in the 30-GHz band, is proposed as the energy receiver in a mm-wave WPT link, exploiting Bessel beam launchers for power transmission. For wearable applications this solution allows to combine the focusing capabilities of the launchers with miniaturization, important requirements for wearable devices. Starting from a rectangular loop length chosen to cover the main beam area, its geometry is outfitted with meandered sections of conductors that act as phase shifters, to ensure uniformity of field distribution and getting rid of field nulls. To further enhance field uniformity, two differential ports, placed in symmetrical positions, are selected and the energy transfer capabilities of the wireless link, consisting of the launcher and the modified loop, are computed by numerical simulations for several distances, both in air and in proximity of human tissues. Two identical differential rectifiers, adopting mm-wave GaAs Schottky diodes, are designed with the proposed two-port loop as the feeding network. An RF-to-dc efficiency of 30 % is predicted for an RF power of 10 dBm at 31.67 GHz. The proposed system can be a feasible solution to be used in compact WPT applications, particularly when wearability, compactness, and lightness are required.