Magnetron

Abstract: A magnetron including: an anode cylinder (1) in which a plurality of vanes (2) are formed, a filament (3) provided at a center of the anode cylinder (11), a top hat (4) which supports an upper end of the filament (3), a top lead (6) for connecting the top hat (4) at an upper end of the top lead (6), an end hat (5) which supports a lower end of the filament (3), an end lead (7) for connecting the end hat (5) at an upper end of the end lead (7), a stem metal (11) hermetically sealed at an open end of the anode cylinder (1) through a pole piece (10), and a choke (12) disposed inside the stem metal (11), wherein the choke (12) is disposed approximately at a distance (C 1 ) of one wavelength of a predetermined high frequency from the top hat (4) along of the top lead (6). It is possible to suppress generation of undesired high frequency, especially of the fifth harmonic, from the input portion.

Description: The present invention relates to a magnetron for generating microwaves, and more particularly, to a magnetron for suppressing the generation of higher harmonics of microwave. A structure relating to a conventional magnetron is known, for example, from JP 02 144 826 as shown in Fig. 6. In Fig. 6, numeral 21 denotes an anode cylinder. In the radially inward direction of the anode cylinder 21, there are formed a plurality of vanes 22, and a filament 23 is disposed on the central axis. The part 24 is a stem metal, which is hermetically sealed at the open end of the anode cylinder 21. The part 25 is a choke which is press-fitted to the inner surface of the stem metal 24. The filament 23 is subjected to high temperature by the applied voltage to discharge thermion, and renders the surrounding area to a high temperature by radiant heat. The discharged thermion shows circulating movement in the operating space formed between the lateral surface of the vane 22 and the filament 23 to oscillate microwave. In general, in the magnetron, there are generated fundamental harmonics as oscillating microwaves. Besides the fundamental harmonic component, there are generated higher harmonics having a frequency of multiple of integers thereof, and these higher harmonics are radiated outside from the input portion. Recently, especially needs for preventing leakage of the electric waves from apparatuses, especially those utilizing magnetron have become greater, and above all, suppression of radiation of higher harmonics is demanded. By the way, in the magnetron to be used for the electronic oven, when the higher harmonic component is radiated from the input side, the component is propagated in the electronic oven in the same manner as in the case of the fundamental harmonics. Because of short wave length, the higher harmonics might provide difficulty to shield the electric waves in various parts of the electronic oven, and cause leakage outside. In view of the above, in order to suppress generation of the higher harmonics by the magnetron per se, there has been developed a technique to suppress optional higher harmonics by forming a 1/4 wavelength type choke on the input portion (e.g., JP 02- 144826 ). In such magnetron, there has not been considered what would be the effect of suppression of the higher harmonics when the position of arrangement of choke is changed. Accordingly, it is an object of the present to provide a magnetron capable of suppressing generation of undesired higher harmonics from the input portion, especially of suppressing generation of the fifth higher harmonics. This object is solved by a magnetron having the technical features according to claim 1. In the inventive constitution, it is desirable that a curled portion is formed at an end of the choke on the filament side, and the curled portion is brought into contact with the stem metal. Fig. 1 is a cross-sectional view of a main portion which shows an embodiment of the present invention; Fig. 2 is a characteristic view to show relation between choke disposition position C1 and suppression effect of the fifth higher harmonics; Fig. 3 is a view to show another example of the gas discharging means in the present invention; Fig. 4 is a view to show yet another example of the gas discharging means in the present invention; Fig. 5 is a view to show still further example of the gas discharging means in the present invention; and Fig. 6 is a cross-sectional view of a main portion in the conventional magnetron. In Fig. 1, an embodiment of the present invention is shown, and description is made based on the drawing hereinafter. The part 1 indicates an anode cylinder, which forms vanes 2 in a radially inward direction of the anode cylinder, and a filament 3 is disposed at a center of the anode cylinder 1. The filament 3 is connected at its upper and lower ends by the top hat 4 and the end hat 5, respectively and supported by them. The top hat 4 and the end hat 5 are connected to the upper ends of the top lead 6 and the end lead 7, respectively, and the top lead 6 and the end lead 7 are fixed to a ceramic metal 8 at their lower portions. The parts 9 and 10 are pole pieces fixed to the upper and lower open ends of the anode cylinder 1, in which a stem metal 11 is hermetically sealed through the input side pole piece 10. The part 12 is a choke disposed concentrically with the stem metal 11 by press-fitting inside the stem metal 11. At an end of the choke 12 on the filament 3 side, a curled portion 13 is formed Positioning is made by bringing the curled portion 13 into contact with the stem metal 11. The curled portion 13 regulates the position of the choke 12 by coming near to or into contact with the pole piece 10 in fitting the stem metal 11 to the pole piece 10, and there is no apprehension to cause displacement of position by temperature variation or vibration during the operation of the magnetron. Accordingly, there is no need to provide means for preventing position displacement such as brazing, and it is possible to set the choke 12 securely at a low cost. Fig. 2 shows how the fifth higher harmonics are suppressed in the case where the distance C1 in a distance along the surface of the top lead 6 from the connecting portion between the filament 3 and the top hat 4 to the disposition position of the choke 12 is varied in the embodiment. It is the characteristics diagram prepared on the basis of the experimental data. As shown in Fig. 2, the suppression effect of the fifth higher harmonics becomes the maximum in the case where the position of the choke 12 is set to a wavelength (24.5 mm) of the fifth higher harmonics, and the farther the distance from the position is, the less the suppression effect is. From the above results, it is concluded that the range having the suppression effect of the fifth higher harmonics in the disposition position C1 of the choke 12 from the connecting portion between the filament 3 and the top hat 4 is C1 = 24.5 ± 1.5 mm. Further, it is more desirable that the disposition is made in the range of C1 = 24.5 ± 1 mm. Further, in the above embodiment, in the case where the distance C2 in a distance along the surface of the end lead 7 from the connecting portion between the filament 3 and the end hat 5 to the disposition position of the choke 12 is varied, there are obtained the characteristics similar to those of Fig. 2. Namely, the suppression effect of the fifth higher harmonics becomes the maximum in the case where the position of the choke 12 is set to a 1/2 wavelength (12.25 mm) of the fifth higher harmonics, and the farther the distance from the position is, the less the suppression effect is. Similar to the above results, the range having the suppression effect of the fifth higher harmonics in the disposition position C2 of the choke 12 from the end hat 5 is C2 = 12.25 ± 1.5 mm. Further, it is more desirable that the disposition is made in the range of C2 = 12.25 ± 1 mm. Furthermore, the effect is greater in the case where the choke 12 satisfies both the above conditions, i.e., where it is disposed in the range of C1 = 24.5 ± 1.5 mm and C2 = 12.25 ± 1.5 mm. More desirably, the range is C1 = 24.5 ± 1 mm and C2 = 12.25 ± 1 mm. By the way, in the magnetron shown in Fig. 6, in order to make the circulation movement of thermion possible, the anode cylinder is subjected to exhaustion of air inside. In this case, the gas lying between the surface of the choke 25 to be press-fitted and the stem metal 24 is discharged from the circular peripheral ends A and B of the press-fitted surface of the choke 25. However, since the gap between the surface of the choke 25 to be press-fitted and the stem metal 24 is very small, in the press-fitting surface of the choke 25 into the stem metal 24, the farther the distance from A and B, the resistance of gas discharging remarkably increases. The gas discharging resistance becomes the largest in the intermediate region between A and B. Especially in that portion, exhaustion of gas is not easy, and there have been cases where the gas remain between the press-fitted surface of the choke 25 and the stem metal 24. The residual gas in such case flows into the anode cylinder 21 due to the lapse of time or the temperature rise in the anode cylinder during the operation, giving rise to troubles such as to inhibit the circulation movement of thermion or to cause combustion of the vane 22 or filament 23 which is in high temperature state during operation, whereby leading to the lowering of yield in process. As a countermeasure against such trouble, conventionally there is a method of removing gas by extending the time for exhaust processing, but such method has not shown sufficient effect. In view of the above, in the present embodiment, as shown in Fig. 1, there are provided, as a gas discharging means, a plurality of approximately circular holes 17 on the surface of the choke 12 to which the stem metal 11 is press-fitted. By the above holes 17 there can be formed, as a gas discharging means, an opening on the outer periphery of the hole, and the distance between the gas discharging means can be shortened compared with the conventional one (distance between A and B). Accordingly, the gas discharging resistance in the intermediate portion between the gas discharging means at which the gas discharging resistance becomes the maximum is made smaller than before, and the rate of the gas to remain on the surface of the choke 12 to be press-fitted to the stem metal 11 after the exhaust processing is lowered. As a result, it is possible to obtain the prescribed vacuum in the anode cylinder 1 with greater certainty. In the above embodiment, there is formed a hole on the surface of the choke 12 to be press-fitted to the stem metal 11. However, as in Fig. 3, a plurality of slit-like notches 17a might be provided on the surface of the choke 12a to be press-fitted to the stem metal 11, or the notches 17a might be formed in other shape. Alternatively, as in Fig. 4, the press-fitting surface of the choke 12b might be formed in a corrugated shape 17b, or as in Fig. 5, the press-fitting surface of the stem metal 11a to which the choke is press-fitted might be of a corrugated shape 17c. According to the present invention, it is possible to suppress generation of undesired high frequency, especially of the fifth high frequency, from the input portion. Furthermore, when gas discharging means is formed on the press-fitting surface between the choke and the stem metal, the gas discharging is facilitated and the predetermined vacuum in the anode cylinder can be obtained in greater certainty.

Claims: A magnetron including: an anode cylinder (1) in which a plurality of vanes (2) are formed in a radially inward direction of the anode cylinder (1), a filament (3) provided at a center of the anode cylinder (1), a top hat (4) which supports an upper end of the filament (3) and connects the filament (3) at a lower end of the top hat (4), a top lead (6) for connecting the top hat (4) at an upper end of the top lead (6), an end hat (5) which supports a lower end of the filament (3) and connects the filament (3) at an upper end of the end hat (5), an end lead (7) for connecting the end hat (5) at an upper end of the end lead (7), a stem metal (11) which is hermetically sealed at an open end of the anode cylinder (1) through a pole piece (10), and a choke (12) disposed concentrically inside and press-fitted into the stem metal (11); characterised in that the press-fitting surface of the choke (12) has a circular peripheral end (B) on the side opposite to the filament (3), wherein the choke (12) is disposed in such a position that said end (B) is approximately in a first distance (C1) along the top lead (6) from the connecting portion between the top hat (4) and the filament (3), said first distance (C1) being the wavelength of the fifth higher harmonics of the fundamental frequency of the magnetron, and/or wherein the choke (12) is disposed in such a position that said end (B) is approximately in a second distance (C2) along the end lead (7) from the connecting portion between the end hat (5) and the filament (3), said second distance (C2) being the ½ wavelength of the fifth higher harmonics of the fundamental frequency of the magnetron. The magnetron of claim 1, wherein a curled portion (13) is formed at an end of the choke (12) on the filament side, and the curled portion (13) is in contact with the stem metal (11). The magnetron of any one of claims 1 to 2, wherein gas discharging means (17a,17b) is formed on a press-fitting surface between the choke (12) and the stem metal (11). The magnetron of claim 3, wherein the gas discharging means (17) is formed on a press-fitting surface of the choke (12). The magnetron of claim 3, wherein the gas discharging means (17c) is formed on a press-fitting surface of the stem metal (11).

Inventors: HASEGAWA SETSUO, MIKI KAZUKI, MURAO NORIYUKI, HASEGAWA, SETSUO, MIKI, KAZUKI, MURAO, NORIYUKI
Applicants: SANYO ELECTRIC CO, SANYO ELECTRIC CO. LTD
Application year: 1997
Main classification: H01J23
IPC codes: H01J23