Yoji Ito
Encyclopedia
was an engineer and scientist that had a major role in the Japanese development of magnetrons and the Radio Range Finder (RRF – the code name for a radar).
of Japan
. His father was the primary schoolmaster and encouraged his children to achieve science and mathematics excellence. After graduating in electrical engineering
from the Tokyo Imperial University, Ito was commissioned in the Imperial Navy and spent several years in assignments at sea.
at the Dresden
Technische Hochschule
. Upon completing his Doctor of Engineering
degree there in 1929, he was promoted to the rank of Commander
and assigned as a researcher at the Naval Technology Research Institute (NTRI) in the Meguro area of Tokyo
. The NTRI had been formed in 1922, and was just becoming fully operational when Ito was sent there. Here first-rate scientists, engineers, and technicians were engaged in a wide variety of activities for advancing naval capabilities.
At NTRI, Ito became involved with analyzing long-distance radio communications, and wanted to investigate the interaction of microwaves with the Kennelly-Heaviside layer
(the ionosphere
). He started a project using a Barkhausen-Kurz tube
, then tried a split-anode cavity magnetron
developed by Kinjiro Okabe
at Tohoku University, but the frequency was too unstable. In late 1932, believing that the magnetron would eventually become the primary source for microwave power, he started his own research in this technology, calling the device a magnetic electric tube.
Shigeru Nakajima, a younger brother of Yoji Ito and a scientist at the Japan Radio Company
(JRC), was also investigating magnetrons, primarily for the medical dielectric heating
(diathermy) market. An alliance was made between NTRI and JRC for further magnetron development. In early 1939, led by Yoji Ito they built a 10-cm (3-GHz), stable-frequency Mandarin-type magnetron (No. M3) that, with water cooling, could produce 500-W power.
in early 1940, including the improvement of strapped cavities. Unlike the high-power magnetron in Great Britain, however, the initial device from the NTRI generated only a few hundred watts.
During 1940, Yoji Ito suggested that the magnetron be used in a microwave collision-avoidance system, assisting naval vessels to navigate in formation. The NTRI and JRC were funded for a demonstration, with the range (distance) to other vessels determined by frequency-modulating the magnetron. This effort was not successful, but it led to the NTRI attempting to find what the Germans were doing in this area. (Japan had joined Germany and Italy in a Tripartite Pact
in 1936.)
The Germans had not yet developed a magnetron suitable for use in such systems, so their equipment operated in the VHF region. At the NTRI, they followed the Germans and built a prototype VHF set operating at 4.2 m (71 MHz) and producing about 5 kW. This was completed on a crash basis, and in early September 1941, the set detected a bomber at a range of 97 km (61 mi). The system, Japan’s first full radar, was designated Mark 1 Model 1 and quickly went into production.
, entering World War II
. Yoji Ito was made a department head at the NTRI and was promoted to Captain. In the war years, he was responsible for many developments in VHF RRF systems, but was most proud of his microwave equipment. He personally led the development of Japan’s first airborne microwave RRF system. This was a 25-cm (1.2-GHz) set producing 2 kW and weighing about 70 kg (150 lb). It was designed for the Gekko night-fighter. He was also involved the Japan’s countermeasure
s equipment, particularly receivers to warn when vessels or aircraft were being observed by American radars.
, in the Shizuoka Prefecture
, for developing a high-power magnetron that, if not as powerful as Tesla had boasted, might at least incapacitate an aircraft. A number of Japan’s leading physicists were involved. A 20 cm magnetron producing 100 kW was achieved, and by the end of the war a 1000 kW (1 MW) unit was undergoing preliminary testing. At that time, the development was terminated and the hardware as well as all documentation was destroyed.
Early years
Yoji Ito was born and raised in Onjuku, a fishing village in the Chiba prefectureChiba Prefecture
is a prefecture of Japan located in the Kantō region and the Greater Tokyo Area. Its capital is Chiba City.- History :Chiba Prefecture was established on June 15, 1873 with the merger of Kisarazu Prefecture and Inba Prefecture...
of Japan
Japan
Japan is an island nation in East Asia. Located in the Pacific Ocean, it lies to the east of the Sea of Japan, China, North Korea, South Korea and Russia, stretching from the Sea of Okhotsk in the north to the East China Sea and Taiwan in the south...
. His father was the primary schoolmaster and encouraged his children to achieve science and mathematics excellence. After graduating in electrical engineering
Electrical engineering
Electrical engineering is a field of engineering that generally deals with the study and application of electricity, electronics and electromagnetism. The field first became an identifiable occupation in the late nineteenth century after commercialization of the electric telegraph and electrical...
from the Tokyo Imperial University, Ito was commissioned in the Imperial Navy and spent several years in assignments at sea.
At the NTRI
Still in the Navy, Yoji Ito was sent to Germany for graduate study where he was a student of Heinrich BarkhausenHeinrich Barkhausen
Heinrich Georg Barkhausen , born at Bremen, was a German physicist.Born into a patrician family in Bremen, he showed interest in natural sciences from an early age...
at the Dresden
Dresden
Dresden is the capital city of the Free State of Saxony in Germany. It is situated in a valley on the River Elbe, near the Czech border. The Dresden conurbation is part of the Saxon Triangle metropolitan area....
Technische Hochschule
Technische Hochschule
Technische Hochschule is what an Institute of Technology used to be called in German-speaking countries, as well as in the Netherlands, before most of them changed their name to Technische Universität or Technische Universiteit in the 1970s and in the...
. Upon completing his Doctor of Engineering
Doctor of Engineering
The Doctor of Engineering is an academic degree awarded on the basis of advanced study and research in engineering or applied sciences...
degree there in 1929, he was promoted to the rank of Commander
Commander
Commander is a naval rank which is also sometimes used as a military title depending on the individual customs of a given military service. Commander is also used as a rank or title in some organizations outside of the armed forces, particularly in police and law enforcement.-Commander as a naval...
and assigned as a researcher at the Naval Technology Research Institute (NTRI) in the Meguro area of Tokyo
Tokyo
, ; officially , is one of the 47 prefectures of Japan. Tokyo is the capital of Japan, the center of the Greater Tokyo Area, and the largest metropolitan area of Japan. It is the seat of the Japanese government and the Imperial Palace, and the home of the Japanese Imperial Family...
. The NTRI had been formed in 1922, and was just becoming fully operational when Ito was sent there. Here first-rate scientists, engineers, and technicians were engaged in a wide variety of activities for advancing naval capabilities.
At NTRI, Ito became involved with analyzing long-distance radio communications, and wanted to investigate the interaction of microwaves with the Kennelly-Heaviside layer
Kennelly-Heaviside layer
The Kennelly–Heaviside layer, named after Arthur Edwin Kennelly and Oliver Heaviside, also known as the E region or simply the Heaviside layer, is a layer of ionised gas occurring between roughly 90–150 km above the ground — one of several layers in the Earth's ionosphere...
(the ionosphere
Ionosphere
The ionosphere is a part of the upper atmosphere, comprising portions of the mesosphere, thermosphere and exosphere, distinguished because it is ionized by solar radiation. It plays an important part in atmospheric electricity and forms the inner edge of the magnetosphere...
). He started a project using a Barkhausen-Kurz tube
Barkhausen-Kurz tube
The Barkhausen-Kurz tube, also called the B-K oscillator, was commonly used in early electronic systems operating in the ultra-high frequency portion of the radio spectrum.-Development:...
, then tried a split-anode cavity magnetron
Cavity magnetron
The cavity magnetron is a high-powered vacuum tube that generates microwaves using the interaction of a stream of electrons with a magnetic field. The 'resonant' cavity magnetron variant of the earlier magnetron tube was invented by John Randall and Harry Boot in 1940 at the University of...
developed by Kinjiro Okabe
Kinjiro Okabe
was a Japanese electrical engineering researcher and professor who made major contributions to magnetron and radar development.One of Japan’s best-known radio researchers in the 1920s-30s era was Professor Hidetsugu Yagi, who was initially at Tohoku University. Kinjiro Okabe was one of Yagi’s first...
at Tohoku University, but the frequency was too unstable. In late 1932, believing that the magnetron would eventually become the primary source for microwave power, he started his own research in this technology, calling the device a magnetic electric tube.
Partnerships
Tsuneo Ito (no relationship to Yoji Ito) at Tokoku University developed an 8-split-anode magnetron that produced about 10 W at 10 cm (3 GHz). Based on its appearance, it was named Tachibana (or Mandarin, an orange citrus fruit). Tsuneo Ito joined the NTRI and continued his research on magnetrons in association with Yoji Ito. In 1937, they developed the technique of coupling adjacent segments (calling it push-pull), resulting in frequency stability, an extremely important magnetron breakthrough.Shigeru Nakajima, a younger brother of Yoji Ito and a scientist at the Japan Radio Company
Japan Radio Company
is a Japanese company specialising in the field of wireless electronics for the communications industry.- History :Established in 1915, the company has produced a wide variety of products including marine electronics, measuring equipment for telecommunications, broadcast radio equipment, and...
(JRC), was also investigating magnetrons, primarily for the medical dielectric heating
Dielectric heating
Dielectric heating, also known as electronic heating, RF heating, high-frequency heating and diathermy, is the process in which a high-frequency alternating electric field, or radio wave or microwave electromagnetic radiation heats a dielectric material. At higher frequencies, this heating is...
(diathermy) market. An alliance was made between NTRI and JRC for further magnetron development. In early 1939, led by Yoji Ito they built a 10-cm (3-GHz), stable-frequency Mandarin-type magnetron (No. M3) that, with water cooling, could produce 500-W power.
Magnetron
The configuration of the M3 magnetron was essentially the same as that used later in the device developed by Boot and RandallHarry Boot
Henry Albert Howard "Harry" Boot was an English physicist who with Sir John Randall and James Sayers developed the cavity magnetron, which was one of the keys to the Allied victory in the Second World War.-Biography:...
in early 1940, including the improvement of strapped cavities. Unlike the high-power magnetron in Great Britain, however, the initial device from the NTRI generated only a few hundred watts.
During 1940, Yoji Ito suggested that the magnetron be used in a microwave collision-avoidance system, assisting naval vessels to navigate in formation. The NTRI and JRC were funded for a demonstration, with the range (distance) to other vessels determined by frequency-modulating the magnetron. This effort was not successful, but it led to the NTRI attempting to find what the Germans were doing in this area. (Japan had joined Germany and Italy in a Tripartite Pact
Tripartite Pact
The Tripartite Pact, also the Three-Power Pact, Axis Pact, Three-way Pact or Tripartite Treaty was a pact signed in Berlin, Germany on September 27, 1940, which established the Axis Powers of World War II...
in 1936.)
VHF
In late 1940. Commander Ito led a technical-exchange mission to Germany. Fluent in the German language and holding a doctorate from Dresden Technische Hochschule, he was well received. Staying several months, he became aware of their pulse-modulated radio equipment for detecting and ranging, and immediately sent word back to Japan that this technology should be incorporated in the NTRI-JRC effort. On August 2, 1941, even before Ito returned to Japan, funds were allocated for the initial development of a pulse-modulated Radio Range Finder (RRF – the Japanese code name for a radar).The Germans had not yet developed a magnetron suitable for use in such systems, so their equipment operated in the VHF region. At the NTRI, they followed the Germans and built a prototype VHF set operating at 4.2 m (71 MHz) and producing about 5 kW. This was completed on a crash basis, and in early September 1941, the set detected a bomber at a range of 97 km (61 mi). The system, Japan’s first full radar, was designated Mark 1 Model 1 and quickly went into production.
RRF
In parallel with the VHF work, Yoji Ito also returned to the magnetron applications, resulting in Japan’s first pulse-modulated microwave RRF set. It operated at 10 cm (3 GHz) and produced a peak-power of 2.0 kW. A prototype was tested in October 1941, and several versions for surface ships and submarines were soon put into production. Naval officials favored the microwave sets because with very narrow beams they were less vulnerable to interception.Pearl Harbor
On December 7, 1941, Japan initiated an attack on Pearl HarborAttack on Pearl Harbor
The attack on Pearl Harbor was a surprise military strike conducted by the Imperial Japanese Navy against the United States naval base at Pearl Harbor, Hawaii, on the morning of December 7, 1941...
, entering World War II
World War II
World War II, or the Second World War , was a global conflict lasting from 1939 to 1945, involving most of the world's nations—including all of the great powers—eventually forming two opposing military alliances: the Allies and the Axis...
. Yoji Ito was made a department head at the NTRI and was promoted to Captain. In the war years, he was responsible for many developments in VHF RRF systems, but was most proud of his microwave equipment. He personally led the development of Japan’s first airborne microwave RRF system. This was a 25-cm (1.2-GHz) set producing 2 kW and weighing about 70 kg (150 lb). It was designed for the Gekko night-fighter. He was also involved the Japan’s countermeasure
Countermeasure
A countermeasure is a measure or action taken to counter or offset another one. As a general concept it implies precision, and is any technological or tactical solution or system designed to prevent an undesirable outcome in the process...
s equipment, particularly receivers to warn when vessels or aircraft were being observed by American radars.
Return to magnetrons
Development at the NTRI continued on magnetrons, resulting in higher and higher power. Yoji Ito and others eventually came to believe that this device might be used as a weapon, encouraged by an earlier newspaper article telling of Nikola Tesla inventing a beam that would “bring down squadrons of aircraft 250 miles away.” In 1943, work began in highest secrecy on a Ku-go (Death Ray) device.Laboratory
A special laboratory was set up near ShimadaShimada, Shizuoka
is a city in Shizuoka Prefecture, Japan. As of February 2010, the city has an estimated population of 100,846 and a population density of 319 persons per km². The total area is 315.88 km².-Geography:...
, in the Shizuoka Prefecture
Shizuoka Prefecture
is a prefecture of Japan located in the Chūbu region on Honshu island. The capital is the city of Shizuoka.- History :Shizuoka prefecture was formed from the former Tōtōmi, Suruga and Izu provinces.The area was the home of the first Tokugawa Shogun...
, for developing a high-power magnetron that, if not as powerful as Tesla had boasted, might at least incapacitate an aircraft. A number of Japan’s leading physicists were involved. A 20 cm magnetron producing 100 kW was achieved, and by the end of the war a 1000 kW (1 MW) unit was undergoing preliminary testing. At that time, the development was terminated and the hardware as well as all documentation was destroyed.
Disbanding of the Japanese military
With the surrender of Japan on August 15, 1945, all organizations, facilities, and projects related to the military in Japan were disbanded. Scientists and engineers, as well as military technical officers, engaged in communications and radar formed the base for Japan's future electronics industry. Captain Yoji Ito was among this large group of individuals.Koden
In 1947, with the hope of making a peaceful contribution of technologies cultivated in his naval days, Dr. Ito founded the Koden Electronics Company Co., Ltd., an affiliate of JRC. Among early products that they conceived was a series of radio direction finders for use in small boat navigation, along with an electronic fish-finder that revolutionized the Japanese commercial fishing industry. Unfortunately, Ito died in 1950, but the firm continues as a worldwide supplier of marine electronic equipment.General references
- Nakagawa, Yasudo; Radar and Related Weapons of World War II, translated and edited by Louis Brown, John Bryant, and Naohiko Koizumi, Aegean Park Press, 1997 ISBN 0894122711
- Swords, S. S.; Technical History of the Beginnings of Radar, Section 4.6, Peter Peregrinus, 1986 ISBN 086341043X
- Watson, Raymond C., Jr.; Radar Origins Worldwide, Chapter 7, Trafford Publishing, 2009 ISBN 1426921101
- Wilkinson, Roger I.; “Short survey of Japanese radar – Part I,” Trans. AIEE, Vol. 65, pp. 370–377, 1946