Magnetron

Details Magnetron Magnetron

1982-05-19

1984-12-18

Chatmon, Saxfield

Electric lamp and discharge devices: systems

Combined load device or load device temperature modifying...

Distributed parameter resonator-type magnetron

313338, 313449, 315 3963, 331 91, H01J 2550

Patent

active

044892543

DESCRIPTION:

BRIEF SUMMARY
TECHNICAL FIELD

The present invention relates to an improvement in a magnetron and, more particularly, to an improvement in a continuous wave oscillation type magnetron suitable for microwave heating in an electronic oven or a pulse oscillation type magnetron suitable for a radar device.


BACKGROUND ART

Electronic equipment which uses a magnetron to generate microwave energy, such as microwave ovens and industrial microwave heating devices, is widely used these days. Along with the development of such electronic equipment, the regulation for suppressing unnecessary radio waves, that is, high frequency noise, has become serve. Noise regulations established by the International Special Committee on Radio Interference (CISPR) are in practice in some countries and are under consideration in other. Therefore, it is desired that measures be taken to further reduce the noise or unnecessary radio waves produced from the magnetron and their leakage.
The conventional structure of the magnetron for microwave ovens and the noise generated therefrom will be described below. FIG. 1 shows the magnetron structure for an microwave ovens of, for example, 2.45 GHz. Reference numeral (21) denotes the magnetron oscillation main body; (22), a radiator; (23), ferrite magnets; (24), the yoke; (25), the spiral directly-heated cathode; (26), the anode vane; (27), the anode cylinder; (28), the strap ring; (29), the output section; (29a), the antenna feeder; (30), the pair of pole pieces; (31), the cathode stem assembly as an input section of the magnetron; (31a), the insulating cylinder; (36), the choke coil; (37), the through type capacitor; (37a), the cathode input terminal; and (38), the shield box. A voltage of several thousands (V) is applied between the anode vane (26) and the cathode (25). A magnetic flux parallel to the axis of the cathode, that is, the axis of the cylinder is induced in an interaction space (39) between the ferrite magnets. Oscillation is thus performed. The oscillated microwave is supplied to an external load from the output section through the antenna feeder. Noise and dominant microwave oscillation are mixed in the microwave oscillation generated from the output section. An unnecessary high frequency noise component is leaked through a filter circuit which comprises the cathode input terminal, the choke coil as part of an input lead wire connected to the cathode input terminal, and a through type capacitor. This noise component varies from several tens Hz to several GHz. The filter circuit acts to attenuate a noise component leaked to a power source transformer and commercial power lines. However, in order to prevent the leakage described above, a high quality filter circuit must be used.
The noise component leaked toward the input lines is measured by the measuring circuit of FIG. 2. As shown in FIG. 3, a spectrum in which the noise component is continuously plotted until near 1,000 MHz is detected. However, in this case, the filter circuit with the choke coil and the capacitor shown in FIG. 1 is not used. Referring to FIG. 2, reference numeral (20) denotes a magnetron similar to the magnetron shown in FIG. 1; (40), a waveguide; (41), a dummy load; (42), a cathode power source; (43), a high voltage power source; (44), cathode input lines; (45), a measuring probe such as a ferrite clamp; and (46), a spectrum analyzer.
The following assumption can be made about the causes of the continuous range of magnetron noise. FIG. 4 illustrates a model of the anode and the cathode which are coaxial to the magnetron. Assume that the cathode is defined as the negative terminal and the anode is defined as the positive terminal, and that a high voltage of several thousands (V) is applied across the magnetron to emit thermoelectrons from the cathode. As indicated by the broken curve (a), the potential curve is of a concave shape and the potential is minimized in the active space (39). Meanwhile, since a DC magnetic field of 1,000 to 2,000 gauss is applied to the active space in the direction of the cathode axis as ind

REFERENCES:
patent: 2784346 (1957-03-01), Dodds
patent: 2808568 (1957-10-01), Cuccia
patent: 2826719 (1958-03-01), Donal, Jr.
patent: 2967264 (1961-01-01), Dench
patent: 3443150 (1969-05-01), Staats
patent: 3742293 (1973-06-01), Chavanat et al.

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