was a Japanese electrical engineering researcher and professor who made major contributions to magnetron and radar development. He did work after the Second World War on medical instruments using ultrasounds. Career Split-anode magnetron One of Japan's best-known radio researchers in the 1920s-1930s era was Professor Hidetsugu Yagi, who was initially at Tohoku University. He 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. Kinjiro Okabe was one of Yagi's first doctoral students and was encouraged by his mentor 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, which 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. Telecommunication 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. Research on radar Technical specialists in the Imperial Navy became interested in the possibility of using radio