A microwave power feed system to a Micro Aerial Vehicle is under development using a 5.8GHz beam irradiated by a phased array antenna. Transmission power is 3.5W and the beam divergence angle is 9deg. The beam is steerable in the range of –9 deg to 9 deg in the x and y directions. The vehicle tracking system is realized using a 2.45GHz microwave pilot signal and the software retrodirective function. A polarity-free patch antenna is proposed as a receiver antenna for constant power supply to a circling vehicle. Its polarity-free characteristics are measured and the antenna shape is optimized.

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Power Transmission to a Micro Aerial Vehicle

*† ‡ § ** †† Wireless energy transmission for an Unmanned/Micro Aerial Vehicle (MAV) has been studied. Electric power for MAV’s propulsion system is provided remotely from the ground power station using 5.8-GHz microwaves. A microwave beam is pointed to the MAV using the phased array technology. The minimum reception antenna radius and maximum steering angle are found in a trade-off relationship. With a two-dimensional array of five 110 mm × 81 mm antennas, 30% of radiated energy can be transmitted to the reception area of 180 mm radius at the height of 2 m.

http://www.al.t.u-tokyo.ac.jp/papers/AIAA-2005-5704.pdf

Wireless Energy Transmission for Micro Aerial Vehicles Using a Microwave Phased Array

A Micro Aerial Vehicle flight system using microwave power supply was developed. In a rectenna system, eight rectennas were arrayed and connected in parallel to drive an electric motor on an MAV model. Output voltage of 250mV and current of 6.8mA was obtained at the altitude of 62cm from the transmitter emitting 3.5W power in total. In a tracking system, two pairs of receiver patch antennas with a leaf pattern were set in rectangular coordinates to detect the position of the MAV while it is circling over the transmitter. Moreover, real time output power measurement was conducted during the MAV circling.

/pdf/a-mav-flight-using-microwave-power-supply-x0k160kdpd.pdf

A MAV Flight Using Microwave Power Supply

We investigate the situation where there are obstructing elements present in the near field of a retrodirective array. We describe three scattering cases, (1) by an array of straight wires, (2) by low loss medium density fibre board partially obscuring the array, and (3) by concrete blocks, totally and then partially obscuring the array. For all scenarios retrodirective action was shown to be able to provide various degrees of automatic compensation for loss in gain relative to that which would have occurred for a conventional (non-retrodirective) array in the presence of the same scattering screens. Gain improvements of up to 10 dB were observed when the retrodirective array was used. In addition we show how the induced variation of received and re-transmited amplitudes across the array, caused by the scattering screens, is the principle mechanism causing deterioration of the retrodirective arrays monostatic response.

Retrodirective Array Performance in the Presence of Near Field Obstructions

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 light-weight rectennas were developed. They are easily mountable on our flying-wing shape MAV model.

/pdf/integration-of-mav-wireless-power-transmission-systems-3njnuskwnr.pdf

Integration of MAV Wireless Power Transmission Systems

This paper presents modeling strategies to determine the operating characteristics of a heterodyne phase-conjugate retrodirective Van Atta (1959) array in the presence of a plane reflector. The models used are based on physical and geometrical optics principles. Predictions of the operating characteristics of the array due to the close proximity of a plane metallic reflector are compared with experimental measurements. It is shown that provided the reflector is positioned at a distance greater than 1.25 times the separation distance between the transmitter and the retrodirective array its effect on the performance of the retrodirective array appears to be negligible.

R. Roy

Papers

Reflector effects on the performance of a retrodirective antenna array