Feasibility Study on Microwave Power Transmission to an Airplane

for Future Mars Observation

Tomohiko Mitani, Masashi Iwashimizu, Akihito Nagahama, and Naoki Shinohara

Research Institute for Sustainable Humanosphere, Kyoto University, Gokasho, Uji-shi, 611-0011 Japan

mitani@rish.kyoto-u.ac.jp

Koichi Yonemoto

Graduate School of Engineering, Kyushu Institute of Technology,

1-1 Sensui-cho, Tobata-ku, Kitakyushu-shi, Fukuoka, 804-8550 Japan

Keywords: Microwave Power Transmission, Magnetron, Rectenna.

Abstract: The objective of the present study is to investigate the feasibility of microwave power transmission to an

airplane for future Mars observation. Airplane is a possibility of Mars observation with wide range and high

resolution, compared to rover or satellite. Since the surface pressure of Mars atmosphere is much thinner than

the Earth, weight reduction is essential to realize airplane flight on Mars. We therefore propose long-time

flight on Mars by using microwave power transmission. We conducted terrestrial experiments of microwave

power transmission to a prototype airplane. We developed a magnetron-based microwave transmitting system,

the frequency of which was fixed with signal injection locking method. Rectennas (receiving antenna +

rectifying circuit) were mounted on the prototype airplane for driving a propeller connected to an electric

motor. Although autonomous flight was not successful yet, we demonstrated that the prototype airplane could

fly by receiving the microwave power.

1 INTRODUCTION

Mars, the fourth planet from the sun, is always of

interest to space scientists and astronomers. Lots of

Mars exploration programs have been executed since

1960s. The Mars rover “Curiosity”, launched in 2011

and landed on Mars in 2012, provides numerous

observation data including images of Martian

landscape and properties of Martian rocks and soils.

Airplane is expected as an alternative Mars

observation sysytem to satellite and rover. It can

move around more widely and quickly than rover, and

can take images with better resolution than satellite.

However the airplane is technically difficult to gain

sufficient aerodynamic lift, because the surface

pressure of Mars is only 0.6 % on Mars of that of the

Earth. Weight reduction of the airplane is therefore

essential to realize the flight on Mars.

We propose microwave power transmission

(MPT) as power supply to a Mars observation

airplane. MPT can reduce the airplane weight by

replacing battery or fuel with rectenna (receiving

antenna + rectifying circuit). It can also realize a long-

time flight by supplying electricity continuously from

a long distance. Figure 1 shows a conceptual image

of a Mars observation airplane driven by MPT. The

transmitting system will be placed on Mars and

electricity will be transferred to the airplane via

microwave. With detecting the airplane position, the

microwave beam will be always focused on the

airplane.

The objective of the present study is to investigate

the feasibility of MPT to an airplane for future Mars

observation. In this paper we describe a magnetron-

based microwave transmitting system, a prototype

airplane, and terrestrial MPT demonstration to the

prototype airplane, with referring to the previous

research outcomes (Iwashimizu, 2014, Nagahama,

2012, 2011).

Mitani T., Iwashimizu M., Nagahama A., Shinohara N. and Yonemoto K.

Feasibility Study on Microwave Power Transmission to an Airplane for Future Mars Observation.

DOI: 10.5220/0005421100470050

In Proceedings of the Third International Conference on Telecommunications and Remote Sensing (ICTRS 2014), pages 47-50

ISBN: 978-989-758-033-8

Figure 1: Conceptual image of a Mars observation airplane

driven by microwave power transmission.

2 SYSTEM REQUIREMENTS OF

TERRESTRIAL EXPERIMENTS

Specifications of Mars observation airplane under

consideration are shown in Table 1. When we utilize

MPT for a Mars observation airplane, the power

required for a propeller motor must be transferred

continuously. Then the power density at the main

wing, on which rectennas will be mounted, is

estimated to be 818 W/m

, assuming that the rf-dc

conversion efficiency of the rectenna is 63 %. Since

we cannot conduct MPT from such a long distance of

100 m as a feasibility study, the estimated power

density becomes the criterion for the power density of

terrestrial MPT experiments.

Table 1: Specifications of Mars observation airplane (under

consideration).

Airplane weight 1.81 kg

Velocity 50.9 m/s

Main wing area 0.256 m

Power required for

motor

132 W

Flight altitude Order of 100 m

The objective of terrestrial experiments is to

realize battery-less stable flight by MPT. A schematic

of the terrestrial experiments is shown in Figure 2.

The experiments were conducted in an anechoic

chamber and the distance from the transmitting

system to a prototype airplane is about 3 m. Under

the configuration, kW-class microwave power is

necessary to meet the required power density. We

therefore adopt magnetron, which is available for

microwave oven, as microwave generator.

Figure 2: Schematic of terrestrial MPT experiments to a

prototype airplane.

3 MAGNETRON-BASED

MICROWAVE TRANSMITTING

SYSTEM

The transmitting frequency of MPT must be fixed

from the viewpoint of rectenna design with high rf-dc

conversion efficiency. Also the output power must be

controlled to realize stable flight because the distance

between the transmitting systems and the airplane

fluctuate constantly. Moreover, the output phase of

each transmitting antenna element must be controlled

when we introduce phased array for the transmitting

system. However a magnetron is a free-running

oscillator and its frequency shifts by its driving

current (anode current), temperature and output load.

We therefore developed a power-variable phase-

controlled magnetron (PVPCM). A great feature of

PVPCM is that its output power can be controlled

with keeping its frequency and phase locked to those

of reference signal. A schematic diagram of a

PVPCM is shown in Figure 3. An injection locking

method (Sivan, 1994) is used for locking the

magnetron frequency to the reference signal

frequency. Also phase synchronization is realized by

comparing phases of the magnetron output and the

reference signal and adjusting the reference signal

phase via the phase shifter 2. The phase shifter 1 is

used for controlling the microwave beam direction

when we apply phased array to the transmitting

system.

We succeeded in developing a PVPCM, whose

frequency was fixed at 2.44575 GHz and whose

output power could be controlled from 450 W to 860

W (Nagahama, 2011).

Third International Conference on Telecommunications and Remote Sensing

Figure 3: Schematic diagram of a power-variable phase-

controlled magnetron (PVPCM).

We demonstrated microwave beam forming by a

phased array composed of two PVPCMs. Figure 4

shows a photograph of the PVPCM phased array.

Two PVPCMs were set in a horizontal plane. The

horn antenna spacing was 0.409 m.

Figure 5 shows experimental results of

microwave beam patterns by the PVPCM phased

array. When two PVPCMs were in phase, the

microwave beam was focused on the broadside

direction. We confirmed that the beam direction was

controlled by setting the phase difference between

two PVPCMs. We obtained the antenna gain of 20

dBi including array factor and element factor of horn

antenna. Also we confirmed that we could adjust the

power density at the receiving point by controlling the

output power.

Figure 4: Photograph of a PVPCM phased array. The

phased array was composed of two PVPCMs.

Figure 5: Experimental results of microwave beam patterns

of the PVPCM phased array.

4 PROTOTYPE AIRPLANE

Figure 6 shows a schematic of a prototype airplane.

The prototype airplane was made of polystyrene foam,

and driven by a propeller attached to an electric motor.

The red circles in Figure 6 indicate the places where

rectennas were allocated. Six rectennas were mounted

on the airplane without interfering with each other in

the light of electromagnetic field.

Figure 7 shows a photograph of our developed

rectenna. The rectenna consisted of cross dipole

antenna and rectifying circuit. The cross dipole

antenna was chosen because it can receive sufficient

microwave power even under a various attitude of the

airplane. The measured rf-dc conversion efficiency of

the rectrenna was 63 % when the output load was 100

Ω (Nagahama, 2012). On the airplane, all the

rectennas were connected in pallalel for the purpose

of impedance matching with the electric motor.

Figure 6: Schematic of a prototype airplane. The red circles

indicate the places where rectennas were allocated.

Reference

Signal

(2.45GHz)

Phase

Shifter1

Phase

Shifter2

Power

divider

Magne‐

tron

RFLO

Lowpass

filter

Circulator

Directional

coupler

Mixer

‐20

‐10

60 70 80 90 100 110 120

Gain (dBi)

Azimuthangle(deg.)

0deg. 90deg. 270deg.

Phasedifferencebetweentwo PVPCMs

Feasibility Study on Microwave Power Transmission to an Airplane for Future Mars Observation

Figure 7: Photograph of a rectenna. The rectenna was

composed of cross dipole antenna and rectifying circuit.

5 DEMONSTRATION FLIGHT

We conducted two types of demonstration flight in

the anechoic chamber: straight flight and circular

flight. Figure 8 shows a photograph of the

demonstration of circular flight. In both cases, the

transmitting system was composed of a single

magnetron and horn antenna. The horn antenna

direction was mechanically controlled towards the

prototype airplane. The output power was 800 W. In

the case of circular flight, the prototype airplane was

suspended from above by gut. We confirmed that the

prototype airplane was driven by MPT in both cases.

Figure 8: Photograph of demonstration flight. The

transmitting system was composed of a single magnetron.

The transmitting antenna direction was mechanically

controlled towards the prototype airplane.

6 CONCLUSION

We succeeded in demonstration flight of the

prototype airplane by MPT without battery and fuel.

Adoption of phased array for the transmitting system

will be the next step for a long-distance and long-time

flight. Precise direction detection of the prototype

airplane will be also necessary to realize autonomous

flight.

ACKNOWLEDGEMENTS

This work was supported by JSPS KAKENHI, Grant-

in-Aid for Challenging Exploratory Research, Grant

Number 25630391.

REFERENCES

Iwashimizu, M., Mitani, T., Shinohara, N., Sasaki, G.,

Hiraoka, K., Matsuzaki, K., Yonemoto K., 2014. Study

on Direction Detection in a Microwave Power

Transmission System for a Mars Observation Airplane.

In IEEE Wireless Power Transfer Conference (WPTC

2014).

Nagahama, A., Mitani, T., Shinohara, N., Fukuda, K.,

Hiraoka, K., Yonemoto K., 2012. Auto Tracking and

Power Control Experiments of a Magnetron-based

Phased Array Power Transmitting System for a Mars

Observation Airplane. In 2012 IEEE MTT-S

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Innovative Wireless Power Transmission:

Technologies, Systems, and Applications (IMWS-IWPT

2012).

Nagahama, A., Mitani, T., Shinohara, N., Tsuji, N., Fukuda,

K., Kanari, Y., Yonemoto K., 2011. Study on a

Microwave Power Transmitting System for Mars

Observation Airplane. In 2011 IEEE MTT-S

International Microwave Workshop Series (IMWS) on

Innovative Wireless Power Transmission:

Technologies, Systems, and Applications (IMWS-IWPT

2011).

Sivan, L., 1994. Microwave Tube Transmitters, Chapman

& Hall, London.

Third International Conference on Telecommunications and Remote Sensing