Large-Scale Sequentially-Fed Array Antenna Radiating Flat-Top Beam for Microwave Power Transmission to Drones

Power beaming is one of the core technologies for microwave power transmission (MPT) systems. Effective plane-to-plane power beaming requires not only high point-to-point efficiency but also appropriately-shaped beam to extract the best performance of receivers (rectennas). Flat-top beam plays an important role in plane-to-plane power beaming for drones where the output dc power from rectennas should be maximized to drive motors. It is challenging to develop a large-scale flat-top-beam array with appropriate distribution circuits. Sequential array is also required to suppress axial ratio on the receiving plane. In this paper, we proposed a simplified but effective way to create a large-scale sequential array for flat-top beam at C-band. The series feed and block-oriented sequential array were adopted to keep the circuit design and fabrication simple while obtaining a sufficient point-to-point efficiency and good axial ratio on the receiving plane. A 196-element phased array with microstrip antennas was developed by subdividing the whole array into four 49-element blocks for simplicity of the circuit design and implementation of block-oriented sequential array. The efficiency between the transmitting ports and the receiving ports was 50.6 % in simulations and 32.0 % in measurements. In the measured flat-top beam, the transmitted power was uniformly concentrated within the receiving plane and the axial ratio of the beam was successfully suppressed to less than 3 dB on most of the receiving area. A flight test of a microwave-powered drone was conducted where a micro-drone successfully flew for seven minutes only with wireless power.