JP3649851B2 - Coaxial magnetron - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to the structure of a getter of a coaxial magnetron, which is a kind of microwave tube used in pulse radar and the like. Among the conventional coaxial magnetrons, the coaxial magnetron having a structure in which the getter is mainly installed at the input terminal portion has a problem that the withstand voltage characteristic of the input portion is likely to be deteriorated due to the structure. On the other hand, in the coaxial magnetron of the present invention, since the getter cavity coupled to the coaxial cavity is separately installed and the getter is installed in the getter cavity, the withstand voltage characteristic of the input unit is deteriorated. That was gone. That is, the present invention relates to an improvement of a getter installation method in a coaxial magnetron.
[0002]
[Prior art]
Here, a typical structure of a conventional coaxial magnetron is shown in the cross-sectional view of FIG. 3, and an outline of the prior art will be described below. First, in the coaxial magnetron, a substantially cylindrical anode cylinder 2 which is substantially coaxial with the coaxial cavity 1 is installed inside a donut-shaped coaxial cavity 1, and a cathode 3 is an anode at the center of the anode cylinder 2. It is installed in a substantially coaxial shape with the cylinder 2. A plurality of anode pieces 4 are installed in the anode cylinder 2 so as to surround the cathode 3 in a substantially coaxial shape, thereby constituting an anode portion. Further, a pole piece 5 and a pole piece 6 for supplying a magnetic field to the anode portion by magnets installed outside the coaxial cavity 1 are provided at both ends of the substantially cylindrical shape of the anode cylinder 2. It is installed so that the piece 4 is sandwiched between them. The coaxial cavity 1 is coupled to the anode portion through a plurality of elongated slits 7 installed in the anode cylinder 2. A tuning mechanism 8 for changing the frequency is installed at one end of the coaxial cavity 1, and an input unit 9 holding the cathode 3 is installed at the other end. A getter 10 for gas adsorption is installed. When a voltage is applied to the input unit 9 in this state, an excited microwave is output from the output unit 11 in the same manner as a normal magnetron.
[0003]
By the way, including the coaxial magnetron described above, in general, the quality of the degree of vacuum in the tube is an important factor for the electrical characteristics of the microwave electron tube. This is because, in a microwave electron tube, when the degree of vacuum deteriorates, the electrical characteristics also deteriorate. For example, if the degree of vacuum is degraded, the microwave output is lowered, the spurious ratio is degraded, and the operating life is shortened. Of course, the coaxial magnetron described above is no exception. Actually, in the coaxial magnetron, mainly the adsorbed gas is released from the metal surface constituting the anode part or the like during the operation, or the decomposed gas is mainly emitted from the electron radioactive material for supplying electrons installed in the cathode 3. As a result, the vacuum in the tube gradually deteriorates. Therefore, in order to suppress the deterioration of the degree of vacuum, it is unnecessary from the metal surface in the tube of the coaxial magnetron or the electron radioactive material of the cathode 3 in the chemical processing step, exhaust processing step, aging processing step, etc. in the manufacturing process. The gas is removed as much as possible. However, in reality, the deterioration of the degree of vacuum in the coaxial magnetron tube with time is unavoidable. Therefore, in order to maintain a good degree of vacuum in the pipe during operation, the coaxial magnetron described above is provided with the getter 10 for gas adsorption on the sleeve of the input unit 9 so that unnecessary gas is adsorbed. is there.
[0004]
Now, with the getter 10, the effect cannot be made to function in the state where it is installed in the pipe. That is, heat treatment called activation is necessary to make gas adsorption possible. Therefore, in general, the getter 10 is heated at a temperature of about 800 (° C.) to about 900 (° C.). There are mainly the following two methods for the heat treatment. The first is a method in which an electrode is installed on the getter 10 from the outside of the tube, and heat treatment is performed by energizing the electrode. The second method is to heat-treat the getter 10 from the outside of the coaxial magnetron where the getter 10 is installed by induction heating with high frequency. The first method requires parts for assembling electrodes and an assembly process, and the production cost is increased as a whole, so that it is not used much. Therefore, the second method is generally used. However, in the second method, it is necessary to configure the outside where the getter 10 is installed with a dielectric. This is to efficiently perform induction heating with high frequency. Therefore, in general, the getter 10 is installed at or near the input unit 9 and is often dielectrically heated by high frequency via insulating ceramics constituting the input unit 9.
[0005]
[Problems to be solved by the invention]
However, as described above, in the coaxial magnetron in which the getter 10 is installed at or near the input unit 9, the withstand voltage of the input unit 9 is reduced because the getter 10 is generally installed. The problem of end up arises. In a coaxial magnetron that supplies a high voltage to the input unit 9, a decrease in the withstand voltage of the input unit 9 causes various problems and may cause a short life. Accordingly, the present invention has been made to solve this problem. A coaxial magnetron having a structure that can easily perform heat treatment for activating the getter 10 without lowering the withstand voltage of the input unit 9 is provided. It is intended to provide.
[0006]
[Means for Solving the Problems]
Therefore, in the present invention, the above problems have been solved by the following means. In the coaxial magnetron in which a tuning mechanism 8 that varies the oscillation frequency by varying the resonance frequency of the coaxial cavity 1 disposed substantially coaxially with the anode cylinder 2 is installed outside the anode cylinder 2, A getter cavity 12 coupled to the cylinder 1 is installed, a getter 10 is installed in the getter cavity 12, and the resonance frequency of the getter cavity 12 is variable in the coaxial cavity 1. It is within the frequency range and outside the normal operating frequency range as a coaxial magnetron.
[0007]
DETAILED DESCRIPTION OF THE INVENTION
The embodiment of the present invention according to the above-described means is shown below with reference to FIGS. FIG. 1 is a sectional view of an embodiment of the present invention, and the outline of the structure is as follows. First, in the coaxial magnetron, a substantially cylindrical anode cylinder 2 which is substantially coaxial with the coaxial cavity 1 is installed inside a donut-shaped coaxial cavity 1, and a cathode 3 is an anode at the center of the anode cylinder 2. It is installed in a substantially coaxial shape with the cylinder 2. A plurality of anode pieces 4 are installed in the anode cylinder 2 so as to surround the cathode 3 in a substantially coaxial shape, thereby constituting an anode portion. Further, a pole piece 5 and a pole piece 6 for supplying a magnetic field to the anode portion by magnets installed outside the coaxial cavity 1 are provided at both ends of the substantially cylindrical shape of the anode cylinder 2. It is installed so that the piece 4 is sandwiched between them. The coaxial cavity 1 is coupled to the anode portion through a plurality of elongated slits 7 installed in the anode cylinder 2. A tuning mechanism 8 for changing the frequency is installed on one end side of the coaxial cavity 1, and an input unit 9 holding the cathode 3 is installed on the other end side. The process so far is the same as that of the conventional coaxial magnetron. However, in the coaxial magnetron according to the present invention, the getter 10 for gas adsorption is not installed on the sleeve of the input part 9. Instead, a getter cavity 12 coupled to the coaxial cavity 1 is installed outside the coaxial cavity 1, and the getter 10 is installed therein. When a voltage is applied to the input unit 9 in this state, an excited microwave is output from the output unit 11 in the same manner as a normal magnetron.
[0008]
The oscillation frequency of the coaxial magnetron that has started operating in this manner can be set to any frequency within a predetermined frequency range by changing the tuning mechanism 8 in the coaxial cavity 1. The tuning mechanism 8 is connected to a mechanically movable structure outside the coaxial cavity 1 so that it can be operated arbitrarily. FIG. 2 is a schematic diagram showing a state of a resonance mode in the coaxial cavity 1 which is in a resonance state at a certain oscillation frequency. The resonance mode in this case is TE011, and the microwave electric field is distributed concentrically with the coaxial cavity 1. In the case of a conventional coaxial magnetron, only the microwave excited in this state is output from the output unit 11. However, in FIG. 2 which is the coaxial magnetron of the present invention, a getter cavity 12 coupled to the coaxial cavity 1 via a slit 13 is installed at a position substantially opposite to the output portion 11. The resonance frequency of the getter cavity 12 is set to be within the variable frequency range of the coaxial cavity 1 and outside the normal operating frequency range of the coaxial magnetron. Therefore, when the oscillation frequency of the coaxial cavity 1 is set by the tuning mechanism 8 so as to be the same as the resonance frequency of the getter cavity 12, the getter cavity 12 is also in a resonance state. Then, the resonance mode is TE011, and the microwave electric field distributed concentrically with the coaxial cavity 1 also enters the getter cavity 12. As a result, heat is generated in the getter cavity 12 due to the consumption of microwaves, and the getter 10 installed in the getter cavity 12 is heated.
[0009]
The amount of getter 10 required depends on the size of the vacuum part of the coaxial magnetron in which it is installed. In general, a coaxial magnetron having a large vacuum portion requires a large amount of gas to be discharged, so that the amount of getter that is inevitably required also increases. On the other hand, the coaxial magnetron having a small vacuum portion has a small amount of gas to be discharged, so that the amount of getter required is naturally reduced. In general, a coaxial magnetron with a large microwave output has a large power loss, that is, heat generation. Therefore, in order to prevent an abnormal temperature rise of the entire coaxial magnetron, the vacuum portion is set as large as possible. Then, in a coaxial magnetron with a large microwave output, the amount of getter that is necessarily required increases. As the amount of getter increases, the power required for activation increases. In the present invention, when the operating frequency is tuned to the resonance frequency of the getter cavity 12, the microwave output is reduced by 10 (%) to 20 (%) as compared with the non-tuned state. This means that the reduced microwave power is consumed in the getter cavity 12. In this embodiment, the average microwave output of the coaxial magnetron was approximately 80 (W), so the average microwave power consumed in the getter cavity 12 was about 8 (W) to about 16 (W). It will be. On the other hand, the installed getter 10 is a non-evaporable getter, and in the conventional method in which an electrode is installed from outside the tube and the heat treatment is performed by energizing the electrode, a direct current of 3.5 (A) is energized Thus, the getter 10 is activated by heat treatment at about 900 (° C.). Since the voltage in this case is about 4.5 (V), the power consumed for the heat treatment is about 15.75 (W). Therefore, it is comparable to the average microwave power consumed in the getter cavity 12 of the present invention, and it is understood that the getter 10 is sufficiently heat-treated and activated in the getter cavity 12 of the present invention. . In this embodiment, the amount of the getter 10 is increased or decreased so that the activation can be sufficiently performed according to the magnitude of the average microwave output of the coaxial magnetron.
[0010]
The structure of the getter cavity 12 is as follows. In this embodiment, the common operating frequency range of the coaxial magnetron is about 9100 (MHz) to about 9600 (MHz), and the variable tuning frequency range is about 8900 (MHz) to about 9800 (MHz). The getter cavity 12 has a cylindrical shape with a diameter of 23.5 (mm) and a length of 12 (mm), and its resonance mode is TM010 of a cylindrical cavity with a resonance frequency of 9771 (MHz). In this way, the resonance frequency of the getter cavity 12 is set to 9771 (MHz) higher than the normal operating frequency of about 9600 (MHz), and the resonance mode is a so-called fundamental mode that resonates at the lowest resonance frequency. Thus, any other resonant mode of the getter cavity 12 does not fall within the normal operating frequency range of about 9100 (MHz) to about 9600 (MHz). Incidentally, the fundamental mode of the resonance mode in this embodiment is TM010, and this fundamental mode is a resonance mode that does not depend on the length direction of the above-mentioned cylindrical shape. Is also an advantage.
[0011]
As described above, the getter 10 installed in the getter cavity 12 is heat-treated and activated, but the getter cavity 12 is within the normal operating frequency range as a coaxial magnetron. Will not resonate and therefore will not affect the normal operation of the coaxial magnetron. This is because the slit 13 is installed in such a structure that the normal operating frequency becomes the cut-off frequency. For example, in this embodiment, since the normal operating frequency range is from about 9100 (MHz) to about 9600 (MHz), if the slit 13 has a slit width of 2 (mm) and a slit length of 10 (mm), the normal operation is performed. Since the slit length is smaller than ½ of the wavelength of the frequency, it becomes the cut-off frequency range. With respect to the dimension of the slit 13, the resonance frequency of the getter cavity 12, that is, 9771 (MHz) is also in the cutoff frequency range. However, the coaxial cavity 1 and the getter cavity 12 are coupled to some extent at the resonance frequency, and when the oscillation frequency is matched with the resonance frequency of the getter cavity 12, the average microwave output is reduced by about 20%. The getter 10 was heat-treated and activated. The dimensions of the slit 13 are appropriately designed in relation to the power required for the getter 10 to be heat-treated and activated, and the minimum necessary conditions are the normal operating frequency range and the cut-off frequency range. The coupling of the coaxial cavity 1 and the getter cavity 12 in the normal operating frequency range is prevented. The slit 13 is not limited to a substantially rectangular shape, and may be a substantially round hole shape. Whether the slit 13 is in the cut-off frequency range is determined by regarding the slit 13 as a waveguide for transmitting microwaves. If the slit 13 has a substantially rectangular shape, the fundamental mode TE10 mode of the rectangular waveguide has a substantially round hole shape. If there is, it is determined by whether or not the TE11 mode of the fundamental mode of the circular waveguide is blocked. In this embodiment, if the slit 13 is substantially rectangular, the slit length is 15.6 (mm) or less. If the slit 13 is substantially round, the hole diameter is 18.3 (mm) or less. is necessary. Incidentally, in the coaxial magnetron of the present invention, a stopper mechanism is provided in the tuning mechanism 8 so as not to be out of the normal operating frequency range during normal use.
[0012]
【The invention's effect】
As described above, in the coaxial magnetron of the present invention, first, since the getter is not installed in the input terminal portion, the withstand voltage characteristic of the input portion is not deteriorated. Therefore, it is effective in reducing the occurrence of defects in the coaxial magnetron, and is useful for extending the service life. Second, since the structure uses the tuning mechanism of the coaxial magnetron itself, material costs, production costs, and the like can be reduced. Thirdly, since no high-frequency induction heating device or the like is required, no equipment cost and maintenance management cost are required.
[Brief description of the drawings]
FIG. 1 is a schematic sectional view of a coaxial magnetron according to an embodiment of the present invention.
FIG. 2 is a schematic diagram of a coaxial magnetron according to an embodiment of the present invention at the time of getter cavity resonance.
FIG. 3 is a schematic sectional view of a conventional coaxial magnetron.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Coaxial cavity 2 ... Anode cylinder 3 ... Cathode 4 ... Anode piece 5 ... Pole piece 6 ... Pole piece 7 ... Slit 8 ... Tuning mechanism 9 ... Input part 10 ... Getter 11 ... ... Output 12 ... Getter cavity 13 ... Slit

Claims (1)

In a coaxial magnetron in which a tuning mechanism for changing an oscillation frequency by changing a resonance frequency of a coaxial cavity installed substantially coaxially with the anode cylinder is connected to the outer side of the anode cylinder, coupled to the coaxial cavity. A getter cavity is installed, a getter is installed in the getter cavity, and a resonance frequency of the getter cavity is within a variable frequency range of the coaxial cavity, and a coaxial magnetron Coaxial magnetron characterized by being outside the normal operating frequency range.

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