First English article of Yagi-Uda antenna

Abstract

Herein, the first English article demonstrating the Yagi-Uda antenna is introduced. The article was originally published in the Proceedings of the Imperial Academy of Japan in 1926.

In 1995, the IEEE Milestone was dedicated to Tohoku University for honoring the great invention of the Yagi-Uda antenna. On the plaque, the following text was noted:

In these laboratories, beginning in 1924, Professor Hidetsugu Yagi and his assistant, Shintaro Uda, designed and constructed a sensitive and highly-directional antenna using closely-coupled parasitic elements. The antenna, which is effective in the higher-frequency ranges, has been important for radar, television, and amateur radio.

The IEEE Milestones program honors remarkable technical achievements in all IEEE-associated fields. The Yagi-Uda Milestone was the first to be dedicated to IEEE Region 10, which includes the IEEE Sections in Asian and Pacific regions. At present, the plaque is located in the Katahira Campus of Tohoku University (Fig. 1).

Fig. 1.

IEEE plaque milestone of Yagi-Uda antenna, mounted in Katahira Campus of Tohoku University. (captured in April, 2024)

The Yagi-Uda antenna comprises parallel linear conducting dipole elements arranged in an end-fire array, a driven element, several directing elements (directors), and reflecting elements (reflectors). It was the first directive antenna to utilize directors positioned in front of the driven element for narrowing the beam. The Yagi-Uda antenna was invented considering that the antenna’s directivity can be increased when the lengths of the directors and spacing between the array elements are well designed. An antenna with high directivity can radiate radio waves in a narrow beam, allowing the transmission of signals over longer distances than an antenna with low directivity. Nowadays, the Yagi-Uda antenna is recognized as crucial with high directivity. Because of its characteristics of high directivity, simple feeding structure, and low wind-pressure, the antenna is widely used in radar, wireless communications, and broadcasting systems. Figure 2 shows a typical Yagi-Uda antenna used for UHF band terrestrial digital TV broadcasting in Japan.

Fig. 2.

(Color online) Typical Yagi-Uda antenna for TV reception; reprinted with permission from the website of Nippon Antenna Co., Ltd.

Tohoku University was found in Sendai in 1907 as Tohoku Imperial University, and the School of Engineering, initially comprising the departments of Mechanical Engineering, Electrical Engineering, and Applied Chemistry, was established in 1919. Hidetsugu Yagi, a founding professor of the Department of Electrical Engineering, advocated for research in telecommunications engineering focusing on areas such as vacuum tubes and antennas rather than the high-power electrical engineering fields such as generators and transformers, which were popular research topics during that time; the Yagi-Uda antenna was invented under these circumstances.

In 1925, Shintaro Uda presented the first report on measurement results, demonstrating that a narrow beam can be easily formed by accurately arranging parasitic elements.¹⁾ However, only an abstract in Japanese appeared in the report.

In 1926, Yagi and Uda published the first English article on the Yagi-Uda antenna in the Proceedings of the Imperial Academy of Japan.²⁾ This was the first detailed description of the Yagi-Uda antenna, covering its geometry and characteristics. The Yagi-Uda antenna, comprising several straight metallic rods acting as reflectors and directors, was demonstrated in this article. The antenna’s geometry, including the length of the directors and reflectors, as well as the spacing between them, was indicated, along with measured radiation patterns that demonstrated its high-directivity characteristics. To visually convey how the radio waves were directed along the director array, they used the term wave canal to illustrate the function of the directors.

Notably, the Yagi-Uda antenna was invented through an experimental approach involving trial and error. However, the presented design provided considerable insights into how to increase antenna directivity via directors. The paper stated that the directors should have a length shorter than half a wavelength, arranged along a line with intervals equal to or greater than a quarter wavelength. Two design examples shown in Figs. 3 and 4 in the original paper indicated that the length of the directors was 0.41 wavelengths, and the interval was 0.34 wavelengths. This antenna design closely aligns with our typical modern design. For example, a four-director Yagi-Uda antenna, shown as a design example in the classic textbook,³⁾ had director lengths of 0.40-0.44 wavelengths, with intervals of 0.31 wavelengths between the directors. This design provided a maximum directivity of approximately 12 dBi and 3-dB bandwidth of 10%.

We do not have straightforward methods for designing the Yagi-Uda antenna using closed-form formulas when the antenna is composed of a large number of parasitic elements as the reflectors or directors. We must rely on computer simulations to understand the behavior of electromagnetic waves related to the antenna geometry by solving Maxwell’s equations. Typically, for a given specification, such as antenna directivity, we first determine the number of directors and reflectors. Next, we optimize the directivity by individually adjusting the lengths of the directors and reflectors, as well as the array spacing, using computer simulations. A Yagi-Uda antenna with high directivity requires a large number of directors and reflectors, and optimizing such antennas often takes a substantial amount of CPU time.

After publishing the paper in the Imperial Academy in 1926, Prof. Yagi visited the USA and presented the Yagi-Uda antenna at several meetings organized by the Institute of Radio Engineers (IRE). In 1928, he published another paper under his name alone in the Proceedings of the IRE.⁴⁾ This paper attracted considerable attention from radio scientists and engineers in the USA and European countries, sparking worldwide interest in the technology of directive antennas at UHF band, which is why the antenna is sometimes called the Yagi antenna or simply the Yagi. However, referring to this antenna as the Yagi-Uda antenna in recognition of Uda’s contribution is common and appropriate.

The history of invention of the Yagi-Uda antenna and the subsequent researches at Tohoku University were introduced in a review paper.⁵⁾

Profile

Qiang Chen received a B.E. degree from Xidian University, Xi'an, China, in 1986 and M.E. and D.E. degrees from Tohoku University, Sendai, Japan, in 1991 and 1994, respectively. At present, he is the Chair Professor of Electromagnetic Engineering Laboratory at the Department of Communications Engineering, School of Engineering, Tohoku University. His primary research interests include antennas, microwave and millimeter wave, electromagnetic measurements, and computational electromagnetics. He received the Best Paper and Zen-ichi Kiyasu Awards from the Institute of Electronics, Information and Communication Engineers (IEICE). He has served as the Chair of IEICE Technical Committee on Photonics-applied Electromagnetic Measurement from 2012 to 2014, IEICE Technical Committee on Wireless Power Transfer from 2016 to 2018, IEEE Antennas and Propagation Society Tokyo Chapter from 2017 to 2018, IEICE Technical Committee on Antennas and Propagation from 2019 to 2021, and Tohoku Branch of IEICE from 2022 to 2023. He is an IEICE Fellow and an International Fellow of The Engineering Academy of Japan.

[From Proc. Imp. Acad., Vol. 2 No. 2, pp. 49-52 (1926)]