Split-anode magnetron tube, an obsolete microwave vacuum tube invented by Albert Hull at General Electric in 1920. One of the first oscillators that could produce frequencies in the gigahertz range, it was used until the modern cavity magnetron was invented in 1940. This tube, used in 1935 in early German experiments in radar was manufactured by AEG/Telefunken and could generate 10 centimeter (3 GHz) microwaves. The image on the right shows the bare tube, about 11 cm tall; on the left shows the tube mounted for use between the poles of a strong permanent magnet.