New small unmanned air vehicles designated as micro air vehicles (MAVs) are increasingly attractive for research, environmental observation, and commercial purposes. As described herein, the feasibility of a system for wireless power transmission via microwaves for MAVs was investigated. For its light weight and flexibility, a textile-based rectenna was proposed for microwave wireless power transmission of MAVs. To investigate bending effects on radiation performance, a microstrip patch antenna with a 5.8 GHz left-hand circular polarization was developed on a textile substrate. The antenna return loss, 20 dB, increased slightly with the antenna bending angle. An axial ratio <3 dB was maintained when the antenna bend angle was <30°. A rectification circuit was formed on the back side felt with sandwiched copper foil as a ground plate. Its weight per unit area was 0.08 g/m2, with maximum rectification efficiency of 58% with 100 Ω load at 63 mW input power. The average and maximum total transmission efficiency using the 5.8 GHz multiple rectenna with a 2.45 GHz retrodirective system were, respectively, 0.44 and 0.60%. The possibility and feasibility of microwave power transmission system using the textile-based rectenna were evaluated.

: A microwave power beaming system was developed to realize wireless power supply to a Micro Aerial Vehicle. This system consists of transmitting, tracking, and receiving systems. In the transmitting system, a 5.8 GHz microwave beam was irradiated from an active phased array antenna. Transmitting power was 4 W and the beam divergence angle was 9 deg. In the tracking system, a 2.45 GHz pilot signal was detected by a two-dimensional tracking antenna and the position was deduced though the software retro-directive function. The maximum tracking error was 1.97 deg in the azimuth direction and 1.79 deg in the radial direction. In the receiving system, a light-weight flexible patch rectenna was developed using felt pad as substrate. The maximum rectenna efficiency of 45.3% was obtained with a 100 Ω road at 63 mW input power. By integrating these systems, auto-tracking wireless power supply was demonstrated to a MAV model circling at the altitude of 1,500 mm. As a result, a motor was kept rotated. Received power was 24.3 mW at maximum and 17.6 mW on average and the total transmission efficiency was estimated at 0.60%.

An auto-tracking wireless power transmitter system for a Micro Aerial Vehicle has been developed. In this paper, a beam transmitter system and a tracking system were combined. A MAV model sending a 2.45GHz pilot signal was tracked by retro-directive function while it was circling over the transmitter at the altitude of 100cm and a 3.5W beam of 5.8GHz microwave was sent back to the MAV by an active phased array. In addition, flexible and lightweight rectennas were developed. They are easily mountable on our flying-wing shape MAV model.

A power beaming system to a Micro Aerial Vehicle (MAV) using 5.8GHz microwaves has been developed. The system consists of three sub-systems; a pointing system, a tracking system, and a receiving system. The MAV is tracked using the phase information of pilot signal. Software retro-directive function has been realized through a PC control and a microwave beam is pointed to the MAV using an active phased array. The beam divergence was about 9deg and the beam steering angle was from -9deg to +9deg. Light-weight flexible rectenna array made of cupper tapes and a thin polyimide film was mounted on a wing of the MAV model, and the electric motor was driven by the received power.The weight per unit reception area was 26mg/cm 2 .