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

VI. CONCLUSION

[5]

In this paper, the practical method to create flat-top beam for

MPT was introduced. Flat-top beam is beneficial to maximize

the received power on a receiving antenna while keeping as

high efficiency as conventional beams. There are almost no

preceding studies which succeeded in making flat-top beam

with a large-scale array. The difficulties in creating flat-top

beam with a large-scale phased array come from the complexity of making a distribution circuit for the appropriate

array weight and the poor quality of axial ratio in the radiated

beam. In our proposal, a 196-element phased array radiating

the flat-top beam was successfully fabricated. Our proposal

includes three main features to make the implementation of

flat-top beam radiation easier and scalable. First, array elements having more than 30 dB lower excitation power than

the highest power were removable. We confirmed the fact that

that removal had almost no impact on the radiation pattern

of the flat-top beam through the simulations and the measurements. Second, to make the circuit design simple, the

whole 196-element array was divided into four blocks of the

same subarrays. It contributes to decreasing the required array

number of distribution from 196 to 49. Those four blocks

were rotated counterclockwise by 90 degrees when creating

the whole array to realize sequential array excitation. It is

confirmed that this block-oriented sequential array method

greatly contributed to suppressing the axial ratio on the receiving plane. The measured axial ratio in most parts of the

receiving area was less than 3 dB. Besides, the design of the

49-way distribution circuit was subdivided into the design of

the horizontal and vertical seven-way dividers. Those sevenway dividers had the same array weight as each other but

the patterns of microstrip lines were different to fit the whole

circuit into a square of 350 mm. Thanks to those methods, we

successfully saved the effort of implementing flat-top beam

with a large-scale array. Finally, we succeeded in flying a

micro-drone for seven minutes only with wireless power from

the developed flat-top-beam array antenna. The transmission

distance was 0.8 m. Moreover, since our proposed method is

scalable, it is applicable to a larger array. Even if the array

size grows fourfold (784 elements), the required steps are just

making two types of 14-way dividers. It means we can easily

extend the transmission distance in drone MPT applications

using a larger phased array.

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Japanese).

NOBUYUKI TAKABAYASHI (Student Member,

IEEE) received the B.E. degree in electrical and

electronic engineering and the M.E. degree in electrical engineering from Kyoto University, Kyoto,

Japan, in 2017 and 2019, respectively, where he

is currently working toward the Ph.D. degree in

electrical engineering.

From 2019 to March 2021, he was an Electrical

Engineer with the Department of Product Development, Space Power Technologies, Inc. His works

include beamformings and antenna prototyping for

wireless power transmission system used in warehouses and factories.

Mr. Takabayashi was the recipient of the Student Award at 2019 Asia

Wireless Power Transfer Workshop and Best Presentation Award at IEEE

AP-S Kansai Joint Chapter in 2019.

KATSUMI KAWAI received the B.E. degree in

electrical and electronic engineering from the Kobe

City College of Technology, Kobe, Japan, in 2019,

and the M.E. degree in electric engineering from

the University of Kyoto, Kyoto, Japan, in 2021.

He is currently working toward the Ph.D. degree

in electric engineering.

His research interests include rectenna and wireless power transfer system design.

306

MIZUKI MASE (Member, IEEE) received the B.E.

degree in electrical and electronic engineering in

2020 from Kyoto University, Kyoto, Japan, where

she is currently working toward the M.E. degree in

electrical engineering.

Her research interests include simultaneous

wireless information and power transfer and orbital

angular momentum multiplexing.

NAOKI SHINOHARA (Senior Member, IEEE)

received the B.E. degree in electronic engineering,

and the M.E. and Ph.D (Eng.) degrees in electrical engineering from Kyoto University, Kyoto,

Japan, in 1991, 1993, and 1996, respectively. In

1996, he was a Research Associate with Kyoto

University, where he has been a Professor since

2010. He has been engaged in research on solar

power station/satellite and microwave power transmission system. He was an IEEE MTT-S Distinguished Microwave Lecturer during 2016–2018,

and is an IEEE MTT-S Technical Committee 25 (Wireless Power Transfer

and Conversion) Former Chair, IEEE MTT-S Kansai Chapter TPC member,

IEEE Wireless Power Transfer Conference founder and ExCom committee

member, URSI commission D Vice Chair, International Journal of Wireless

Power Transfer (Hindawi) Executive Editor, the First Chair and Technical

Committee member on the IEICE Wireless Power Transfer, Japan Society of

Electromagnetic Wave Energy Applications Adviser, Space Solar Power Systems Society Vice Chair, Wireless Power Transfer Consortium for Practical

Applications (WiPoT) Chair, and Wireless Power Management Consortium

Chair. His books are Wireless Power Transfer via Radiowaves (ISTE Ltd. and

Wiley) Recent Wireless Power Transfer Technologies via Radio Waves (ed.)

(River Publishers), and Wireless Power Transfer: Theory, Technology, and

Applications (ed.) (IET), and some Japanese textbooks of WPT.

TOMOHIKO MITANI (Member, IEEE) received

the B.E. degree in electrical and electronic engineering, the M.E. degree in informatics, and the

Ph.D. degree in electrical engineering from Kyoto

University, Kyoto, Japan, in 1999, 2001, and 2006,

respectively.

In 2003, he was an Assistant Professor with the

Radio Science Center for Space and Atmosphere,

Kyoto University, where he has been an Associate Professor with the Research Institute for Sustainable Humanosphere since 2012. His research

interests include the experimental study of magnetrons, microwave power

transmission systems, and applied microwave engineering.

Dr. Mitani is a member of the Institute of Electronics, Information, and

Communication Engineers, Japan, and Japan Society of Electromagnetic

Wave Energy Applications. Since 2015, he has been a board member of

JEMEA. He was the Treasurer of the IEEE MTT-S Kansai Chapter from 2014

to 2017, and has been since 2019.

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