Hidetsugu Yagi Yagi Antenna

Hidetsugu Yagi Yagi Antenna

The Yagi Antenna is a directional antenna invented by Dr. Hidetsugu Yagi of Tohoku Imperial University and his assistant, Dr. Shintaro Uta. This groundbreaking invention combined a simple structure with high performance. Most ultra short or extremely short wave receiving antennas, such as TV antennas, use this structure.

Dr. Yagi's invention was ahead of its time (patented in 1940) and therefore not understood in Japan. Its value was, however, accepted in Europe and North America, where it entered commercial production. It is said that people in Japan realized the true value of the Yagi Antenna in World War 2 when it was discovered that the invention was used as a radar antenna by the Allies.

Dr. Yagi and his Yagi Antenna
(Photo: Hitachi Kokusai Electric, Inc. Yagi Antenna Division)

Sixty-five years ago this month, THE PROCEEDINGS OF THE INSTITUTE OF RADIO ENGINEERS ( IRE) included a paper on short-wave communication by Hidetsugu Yagi, an Engineering Professor at Tohoku Imperial University in Sendai, Japan. In the paper, he discussed the design and performance of a directive antenna that he called a "wave projector" or "wave canal" and which had been developed recently at Tohoku University. The antenna employed a number of parasitic elements called directors and reflectors and would come to be known as the Yagi antenna or Yagi-Uda antenna. Yagi also provided data on a split-anode magnetron which one of his students, Kinjiro Okabe, had used to generate oscillators down to around 12 cm in wavelength. Yagi stated that he and his colleagues had tested a system using a magnetron at 40 cm along with a wave projector antenna to achieve a range of about 1 km. He commented that the performance of the wave projector had been "demonstrated to be quite remarkable." They had tested antennas with up to 20 directors, and he explained how the beam width was affected by the number and length of the parasitic elements. During the discussion of Yagi's paper, J. Howard Dellinger, of the U.S. Bureau of Standards, predicted that the paper would be regarded as a classic and that the principles disclosed by Yagi would serve as a guide for much future development.

Yagi was born in 1886 in Osaka, Japan, and graduated in engineering from Tokyo Imperial University in 1909. He then went to Germany, where he continued his education under the direction of Heinricti Barkhausen, inventor of the Barkhausen oscillator, which used a positive-grid triode to generate high frequencies. Yagi's research in Germany concerned resonant transformers used in wireless systems. The outbreak of the first World War forced his hurried departure without his experimental data. He later published a paper on the theoretical part of this research in the December 1917 PROCEEDINGS OF THE INSTITUTE OF RADIO ENGINEERS. After leaving Germany, Yagi studied in Great Britain with John A. Fleming until 1916. Before returning to Japan, Yagi visited the United States and spent some time at Harvard University with George W. Pierce. Yagi then began his teaching career at Tohoku University, which awarded him a doctorate in engineering in 1919.

At Tohoku, Yagi initiated a research program in radio-electronics drawing on what he had learned from Barkhausen, Fleming, and Pierce. Other members of the faculty and advanced students, including Okabe and Shintaro Uda, became participants in a collective research effort. A perceived need for better communication between islands and with ships led them to focus on short wave communication with directive antennas. The Yagi group received financial support for the research from a private foundation in Sendai. In February 1926, Yagi and Uda published their first report on the wave projector antenna in a Japanese publication. Yagi applied for patents on the new antenna both in Japan and the United States. His U.S. patent was issued in May 1932 and assigned to the Radio Corporation of America.

In 1928, Yagi made a second visit to the United States and gave talks on the Japanese short wave research at IRE meetings in several cities and for a group of engineers at General Electric. His visit stimulated a renewed interest in magnetrons at GE and they developed a 400-MHz magnetron and tested it with a wave projector during the summer of 1928. Bureau of Standards engineers also used a Yagi-Uda antenna in an experimental aircraft landing system in 1930. In 1933 the short-wave system developed at Tohoku University was used to establish a government radio telephone link between Sakata and Tobishima Island, a distance of about 40 km.

In the early 1930s Yagi moved to Osaka Imperial University as Director of a laboratory where developmental work on radar began by 1936. He served as a Civilian Consultant on radar and communication to the Japanese military during World War II. His home and library along with most of his personal papers were lost during a bombing raid in April 1945. Soon after the end of the war he was interviewed by Roger I. Wilkinson, William R. Hewlett, and others concerning Japanese developments during the war. Yagi expressed considerable frustration over what he perceived as poor communication and cooperation between the military services and civilian experts. Gentai Sato, who studied under Yagi, has written on the surprise to the Japanese when they captured British radars equipped with Yagi antennas and a document on Yagi arrays at Singapore. Sato also noted the irony in the American use of Yagi antennas installed on the atomic bombs dropped on Japan to determine the height of the explosion. Shintaro Uda visited the United States in 1951 and expressed his astonishment at the ubiquity of the Yagi-Uda antennas used as home television antennas.

After the war Yagi served as a consultant on the technologica1 rehabilitation of Japan and assisted in the formulation of television standards. He also served as president of the Yagi Antenna Company and was awarded Japan's Order of Cultural Merit in 1956. He died in 1976.