A statistical study of magnetron patents in the early years of electronics between 1920 and 1945; heuristic foucusing around the discovery of the cavity magnetron

The patents related to major magnetron innovations are now well known, but historical studies tend to concentrate on a small number of patents representative of significant advances in technology. Between the 1920s and the end of WW2, more than 2360 patents related to the magnetron were filed and show all the companies and inventors involved in its development. Research on the magnetron was stimulated by the radio broadcasting industries in the early 1930s. A study of the patents shows the strategy of the companies involved in magnetron research. One of the aspects of this strategy was that companies filed patents in other countries, to counter concurrence and to win a new market share. This paper tries also to show the technical evolution of the magnetron in a context of an economic war within the young radio industry. For these reasons and proved by the great number of patents, technological progress until the late 1930s was almost exclusively due to industries. Although there are several explanations in different sources of the discovery by Randall and Boot of the cavity magnetron, the author proposes a hypothesis, through some of patents which came some time before, of the anteriority of cavities. In addition, the author proposes the method using patent classification can be considered as heuristic for such questions.