Noise-Reduction Effects of Oven Magnetron With Cathode Shield on High-Voltage Input Side

A magnetron with a metallic cathode shield on the high-voltage (HV) input side is newly designed for the purpose of reducing the spurious noise generated from an oven magnetron. In this paper, it was experimentally found that the newly designed magnetron suppressed the sideband noise around the carrier frequency up to 10 dB, compared to the conventional magnetron. Moreover, both the spurious noise in the high frequency bands (4–14 GHz) and the line noise in the low frequency bands ($sim$1 GHz) from the newly designed magnetron were reduced up to 30 dB, compared to the conventional one. It was also found that a cathode shield attached to only the HV input side was more effective than the cathode shields attached to both the HV input side and the RF output side, with respect to the noise reduction. The thermionic emission from the cathode filament and the motions of the electrons in a magnetron are discussed in investigating the noise-reduction mechanisms.