Office of Technology Transfer – University of Michigan

Low Noise Magnetron and Crossed-field Amplifier by Azimuthally Varying Axial Magnetic Field

Technology #2512

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Ronald M. Gilgenbach
Managed By
Keith Hughes
Assistant Director, Physical Sciences & Engineering 734-764-9429


The noise generation mechanisms of linear electron beam devices are well-known. Generally, fluctuations of cathode electron emission excite space charge waves, which propagate along the electron beam. Calculations and computations of noise figures in linear devices agree with experiments. Methods of noise suppression in linear tubes are at a very advanced stage. On the other hand, noise generation mechanisms in cross-field devices are not presently understood and predictive computational calculations do not exist. Methods of noise suppression in crossed-field devices have not previously been practically realized.


University of Michigan researchers have developed a low-noise, crossed-field device, such as a microwave magnetron, a microwave oven utilizing same, crossed-field amplifier and a method of converting a noisy magnetron to a low-noise magnetron. The device includes an electrical circuit for generating a radial electrical field, and a magnetic circuit for generating an axial magnetic field substantially perpendicular to the radial electric field. The magnetic configuration reduces and eliminates microwave and radio frequency noise. This microwave noise is present near the carrier frequency and as sidebands, far separated from the carrier. The device utilizes azimuthally varying, axial, magnetic field perturbations. In one embodiment, at least one permanent magnet is placed against the azimuthally-symmetric, axial magnetic field magnetron magnets (four magnets work especially well). This additional permanent magnet(s) causes the axial magnetic field to vary azimuthally in the magnetron and completely eliminates the microwave noise and unwanted frequencies.

Applications and Advantages


  • Reduction of interference with telephone-nl-and computer communications by microwave-nl-magnetrons in microwave ovens
  • Lighting and industrial heating, where-nl-noise-free magnetrons can be used
  • Applications in which precise microwave-nl-frequency is desired
  • Reduction of noise in crossed-field-nl-amplifiers


  • Completely eliminates the microwave noise and unwanted frequencies