magnetronbuis

A magnetronbuis, or magnetron tube, is a type of vacuum tube that generates microwaves by the interaction of a beam of electrons with resonant cavities in a strong magnetic field. In Dutch usage the term magnetronbuis is common; in English, the device is typically called a magnetron, specifically a cavity magnetron for the high-frequency variant.

The most common design is the cavity magnetron, consisting of a heated cathode inside a cylindrical anode block with an array of hollow resonant cavities around the circumference, enclosed by magnets that provide the static magnetic field.

Operation relies on electron emission from the cathode forming a current that, under the influence of the magnetic field, follows curved paths and interacts with the RF fields in the cavities. This interaction extracts energy from the electron beam and converts it into microwave radiation, which is released through a resonant launcher into a waveguide or antenna. The operating frequency is largely determined by the dimensions of the cavities and typically ranges from hundreds of megahertz to several gigahertz; household microwave ovens commonly use around 2.45 GHz.

History and use: The cavity magnetron was developed in the early 1940s by John Randall and Harry Boot at the University of Cambridge and played a pivotal role in radar technology during World War II, enabling compact, high-power microwave sources. Since then, magnetron tubes have found use in radar, microwave communications, industrial heating, and consumer microwave ovens. They are praised for high efficiency and simple construction but tend to have broad bandwidth and fixed frequency characteristics. In many applications, tunable sources such as klystrons or traveling-wave tubes are preferred for frequency agility, though magnetrons remain common for fixed-frequency, high-power microwave generation.