Life begins at forty: Microwave tubes

The history of microwave tubes is reviewed from a philosophical viewpoint. An interesting part of this historical assessment is an examination of roles of technical forecasting and management planning. The definition of the microwave frequency range is presented and shown to support the primacy of tubes, or electron-beam devices, in a frequency range between those dominated by discrete solid-state devices and lasers. A generalized device theory is shown to be useful in assessing limitations and potentials. The magnetron has a unique place as the microwave component of by-far greatest production volume associated with microwave-oven boom. New elements in the long-range future of microwave tubes include expanding power applications, cross-fertilization with other device disciplines, the controversial millimeter-wave potential, and increasing attention to the potential for RFI and radiation hazards. If history is any guide, we can expect some further surprises in this field.