The Yagi Antenna

#Behind-the-scenes stories of Japanese patents.

This is something I sometimes mention when I give outside lectures. Those of you who are Korean may never have heard of it.

There was a Japanese man named Yagi.

Those of you in the generation of the 1970s and 80s will all remember this, but back then every house that had a television had a TV antenna. The shape was like the one shown below.

In Japan, this antenna was called the Yagi antenna. So the person who invented this antenna was, presumably, a man named Yagi.

In the 1920s, at Tohoku Imperial University, it was discovered by chance that an antenna made of metal rods had excellent sensitivity, and research was carried out repeatedly. (Since the lecturer Uda also took part in the research at this time, it is also called the Yagi-Uda antenna.)

(For reference, there were seven imperial universities in Japan, or nine including those in Seoul and Taiwan. Tohoku University is located in Sendai, where the Tohoku earthquake occurred not long ago.)

In 1926, it was granted Japanese Patent No. 69252 as a "variable-directivity radio wave generating device." In the same year, two patents each were also obtained in the United States and the United Kingdom.

In 1928, lectures were given in the United States as well, and as a result of this, GE was prompted to vigorously pursue research on the magnetron. The problem was that in Japan it was rather neglected.

This was gradually developed further, and in the United States it evolved into a system that could safely guide aircraft to airports even under poor visibility, such as at night.

During the Battle of Britain in 1940, many radars and fighter aircraft used the Yagi antenna to counter German air raids, and for German pilots it was a radar to be feared.

The next is a famous story: in the 1942 Battle of Singapore, when Japanese forces took British soldiers prisoner, they found the words "yagi antenna" in the notebook of a British intelligence officer and interrogated him about it. They were astonished to learn it was the name of a Japanese inventor—a fact they reportedly found hard to believe. In other words, in Britain and elsewhere the Yagi antenna was used to develop many excellent radars, yet in Japan it had not been utilized at all.

Ironically, when Japan attacked Pearl Harbor in 1941, it is said that radar using the Yagi antenna had already detected the movement of aircraft from as far as 200 kilometers away. (Although, of course, they were mistaken for friendly aircraft.)

It was the 1942 air raid on Tokyo that made Japan, too, realize the necessity of radar, and it began to take an interest in the Yagi antenna.

It is said that the greatest cause of Japan's defeat at the Battle of Midway in 1942—the turning point of the Pacific War—was the Allied radar that used the Yagi antenna.

The most ironic fact of all is that the atomic bomb dropped on Hiroshima was equipped with radar that used the Yagi antenna.

It is said that Uda, the co-developer, was astonished when he visited the United States after the war and saw that the antenna he had developed was being used on the TV antennas of homes everywhere.

Afterward, the Yagi antenna came to be installed in homes throughout our country (Korea) as well.

Had the Second World War not occurred, Yagi might well have received royalties from Britain or the United States. The antenna was for defensive use, and so it is an irony that it was not utilized in Japan, where the emphasis was on offense.