Kinjiro Okabe
Encyclopedia
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 doctoral students. Yagi had become very interested in the magnetron, built and named by Albert W. Hull at General Electric
in 1921. While Hull’s magnetron was a HF
device, Yagi was convinced that it could also be a generator of VHF or even UHF signals, and encouraged Okabe in this pursuit.
In 1926, Okabe developed a magnetron device that significantly decreased the operating wavelength of oscillations. He filed for a U.S. patent in 1926, and it was granted in 1929 (No. 1,735,294). His work continued, and, based on developing the split-anode device, he was awarded the Doctor of Engineering degree in 1928.
Okabe first published his findings in a Japanese journal, and followed with a foundational paper in the prestigious Proceedings of the IRE. While Hull had published on the HF magnetron years earlier, it was only after Okabe’s detailed paper on generation at 17 cm that this device gained world interest. Although this was the first microwave magnetron, it was not immediately applied in communications because it was not frequency stable.
Another of Yagi’s early doctoral students, Shintaro Uda
, had worked with Yagi in developing an antenna using a radically new configuration that they called a wave projector. Commonly called the Yagi-Uda antenna, this was soon used by Yagi, Okabe, and Uda in demonstrating a 40-cm microwave system with a magnetron and wave projector that achieved a transmission distance of about 1 km. This and other activities at the Tohoku Radio Laboratory was described in a 1928 seminal paper by Yagi.
In the early 1930s, Yagi moved to the Osaka Imperial University
, where he was appointed Director of the Radio Research Laboratory. Okabe accompanied Yagi to Osaka and continued his research on magnetrons, ultimately making a split-anode device that generated oscillations at wavelengths down to about 12 cm (2.5 GHz). He also developed a hot-cathode discharge device (called the Osaka tube) that had characteristics similar to the Barkhausen-Kurz tube
.
Technical specialists in the Imperial Navy became interested in the possibility of using radio to detect aircraft. For consultation, they turned to Professor Yagi who suggested that this might be done by examining the Doppler frequency-shift in a reflected signal. Funding was provided to the Osaka Laboratory for experimental investigation of this technique; Kinjiro Okabe was assigned to lead the effort. His theoretical analysis indicated that the reflections would be greater if the wavelength was approximately the same as the size of aircraft structures.
Okabe developed an experimental apparatus using a VHF transmitter and receiver with Yagi-Uda antennas separated some distance. In 1936, he successfully detected a passing aircraft by the Doppler-interference method; this was the first recorded demonstration in Japan of aircraft detection by radio. With this success, Okabe’s research interest switched from magnetrons to VHF equipment for target detection.
The funding for Okabe’s target detection project was not continued; the top levels of the Imperial Navy believed that any advantage of using radio for this purpose were greatly outweighed by enemy intercept and disclosure of the sender’s presence.
Okabe continued to devote much of his research to improving magnetrons. Although this technology was picked up by other organizations, including the Naval Technology Research Institute where Yoji Ito
led in further improvements and the eventual incorporation in detection system for the Japanese military, Okabe continued to publish in the open literature.
During and following the war years, Okabe remained very active at the Osaka Laboratory. In 1955, his interest turned to medical applications of ultrasound, and he suggested to Shigeo Satomura, one of his graduate students, that he apply Doppler
ultrasound
techniques to medical diagnosis. This research was very productive, and led to new applications of this technology.
While Okabe’s initial proposal for radio detection was not accepted by the military, time would see this position greatly change. The 1944 Order of Culture
award for significant advancements in science and technology was presented to Okabe by the Emperor of Japan in recognition of his early efforts.
Radar
Radar is an object-detection system which uses radio waves to determine the range, altitude, direction, or speed of objects. It can be used to detect aircraft, ships, spacecraft, guided missiles, motor vehicles, weather formations, and terrain. The radar dish or antenna transmits pulses of radio...
development.
One of Japan’s best-known radio researchers in the 1920s-30s era was Professor Hidetsugu Yagi
Hidetsugu Yagi
Hidetsugu Yagi was a Japanese electrical engineer. When working at Tohoku University, he wrote several important articles that introduced a new antenna design by his colleague Shintaro Uda to the English-speaking world.The Yagi antenna, patented in 1926, allows directional communication using...
, who was initially at Tohoku University. Kinjiro Okabe was one of Yagi’s first doctoral students. Yagi had become very interested in the magnetron, built and named by Albert W. Hull at General Electric
General Electric
General Electric Company , or GE, is an American multinational conglomerate corporation incorporated in Schenectady, New York and headquartered in Fairfield, Connecticut, United States...
in 1921. While Hull’s magnetron was a HF
High frequency
High frequency radio frequencies are between 3 and 30 MHz. Also known as the decameter band or decameter wave as the wavelengths range from one to ten decameters . Frequencies immediately below HF are denoted Medium-frequency , and the next higher frequencies are known as Very high frequency...
device, Yagi was convinced that it could also be a generator of VHF or even UHF signals, and encouraged Okabe in this pursuit.
In 1926, Okabe developed a magnetron device that significantly decreased the operating wavelength of oscillations. He filed for a U.S. patent in 1926, and it was granted in 1929 (No. 1,735,294). His work continued, and, based on developing the split-anode device, he was awarded the Doctor of Engineering degree in 1928.
Okabe first published his findings in a Japanese journal, and followed with a foundational paper in the prestigious Proceedings of the IRE. While Hull had published on the HF magnetron years earlier, it was only after Okabe’s detailed paper on generation at 17 cm that this device gained world interest. Although this was the first microwave magnetron, it was not immediately applied in communications because it was not frequency stable.
Another of Yagi’s early doctoral students, Shintaro Uda
Shintaro Uda
Japanese inventor. Assistant of professor Hidetsugu Yagi at Tohoku University, where they invented the Yagi-Uda antenna in 1926. 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...
, had worked with Yagi in developing an antenna using a radically new configuration that they called a wave projector. Commonly called the Yagi-Uda antenna, this was soon used by Yagi, Okabe, and Uda in demonstrating a 40-cm microwave system with a magnetron and wave projector that achieved a transmission distance of about 1 km. This and other activities at the Tohoku Radio Laboratory was described in a 1928 seminal paper by Yagi.
In the early 1930s, Yagi moved to the Osaka Imperial University
Osaka University
, or , is a major national university located in Osaka, Japan. It is the sixth oldest university in Japan as the Osaka Prefectural Medical College, and formerly one of the Imperial Universities of Japan...
, where he was appointed Director of the Radio Research Laboratory. Okabe accompanied Yagi to Osaka and continued his research on magnetrons, ultimately making a split-anode device that generated oscillations at wavelengths down to about 12 cm (2.5 GHz). He also developed a hot-cathode discharge device (called the Osaka tube) that had characteristics similar to the 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:...
.
Technical specialists in the Imperial Navy became interested in the possibility of using radio to detect aircraft. For consultation, they turned to Professor Yagi who suggested that this might be done by examining the Doppler frequency-shift in a reflected signal. Funding was provided to the Osaka Laboratory for experimental investigation of this technique; Kinjiro Okabe was assigned to lead the effort. His theoretical analysis indicated that the reflections would be greater if the wavelength was approximately the same as the size of aircraft structures.
Okabe developed an experimental apparatus using a VHF transmitter and receiver with Yagi-Uda antennas separated some distance. In 1936, he successfully detected a passing aircraft by the Doppler-interference method; this was the first recorded demonstration in Japan of aircraft detection by radio. With this success, Okabe’s research interest switched from magnetrons to VHF equipment for target detection.
The funding for Okabe’s target detection project was not continued; the top levels of the Imperial Navy believed that any advantage of using radio for this purpose were greatly outweighed by enemy intercept and disclosure of the sender’s presence.
Okabe continued to devote much of his research to improving magnetrons. Although this technology was picked up by other organizations, including the Naval Technology Research Institute where Yoji Ito
Yoji Ito
was an engineer and scientist that had a major role in the Japanese development of magnetrons and the Radio Range Finder .-Early years:...
led in further improvements and the eventual incorporation in detection system for the Japanese military, Okabe continued to publish in the open literature.
During and following the war years, Okabe remained very active at the Osaka Laboratory. In 1955, his interest turned to medical applications of ultrasound, and he suggested to Shigeo Satomura, one of his graduate students, that he apply Doppler
Doppler effect
The Doppler effect , named after Austrian physicist Christian Doppler who proposed it in 1842 in Prague, is the change in frequency of a wave for an observer moving relative to the source of the wave. It is commonly heard when a vehicle sounding a siren or horn approaches, passes, and recedes from...
ultrasound
Ultrasound
Ultrasound is cyclic sound pressure with a frequency greater than the upper limit of human hearing. Ultrasound is thus not separated from "normal" sound based on differences in physical properties, only the fact that humans cannot hear it. Although this limit varies from person to person, it is...
techniques to medical diagnosis. This research was very productive, and led to new applications of this technology.
While Okabe’s initial proposal for radio detection was not accepted by the military, time would see this position greatly change. The 1944 Order of Culture
Order of Culture
The is a Japanese order, established on February 11, 1937. The order has one class only, and may be awarded to men and women for contributions to Japan's art, literature or culture; recipients of the order also receive an annuity for life...
award for significant advancements in science and technology was presented to Okabe by the Emperor of Japan in recognition of his early efforts.