Efficient rectenna design for wireless power transmission for MAV Applications

Abstract

This thesis is a continuation in part of a NPS project relating to wireless transmission of power to a MAV. The conversion of rf power into usable dc power is done by a rectifying antenna or rectenna. The emphasis of this thesis is an indepth study of all components of the rectenna to determine the limitations of an existing design which has low efficiency, and to determine improvements to the design, specifically for MAV applications. Studies relating to each rectenna subsystem were conducted, highlighting improvements and design trade-offs. The analysis of the rectenna is broken into four subsystem, namely, (1) the receiving antenna, (2) the pre-rectification filtering, (3) the rectification and lastly, (4) post-rectification filtering. From the findings of this thesis, the final rectenna design implemented a capacitive probe fed circular patch that exhibits relatively wide bandwidth, high tolerance to manufacturing variances, and a radiation efficiency of 95%. The pre-rectification filter was re-designed to increase its transmittance characteristics to 94%. The Schottky diode was re-analyzed and its conversion efficiency and trade-offs for MAV applications were documented. The post-rectification filter was reconstructed taking into consideration the positioning of the Schottky diode, and impedance matching for both antenna and Schottky diode was explained. The issue of microstrip discontinuities and probe feed connection was subsequently addressed. The final design has a dimension of approximately 112.5 mm2 which is only 15% of the existing design, and has an estimated weight of less than a gram. The estimated rf-to-dc conversion efficiency is approximately 50%.