JPS6316852B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a magnetron, and particularly to improvements in its cathode structure. In general, magnetrons that apply a magnetic field at right angles to an electric field are now widely used in electronic devices such as microwave ovens, and as a result, regulations regarding noise leakage have become stricter.
Regarding this noise regulation, internationally, the standards of the International Special Committee on Radio Interference (CISPR) are being implemented or are being considered for implementation in each country. Therefore, with this type of electron tube, it is natural to reduce the noise emitted from the electron tube itself, to emit unnecessary radio waves,
Measures to further reduce leakage are required. Taking a magnetron as an example, the conventional structure and noise generation situation will be explained next. For example, the structure of a 2.45 GHz microwave oven magnetron is shown in Figure 1. In the figure, reference numeral 21 is the main body of the magnetron oscillation unit, 22 is the radiator, 23, 23
24 is a ferrite magnet, 24 is a yoke, 25 is a spirally wound directly heated cathode, 26 is an anode vane, 27 is an anode cylinder, 28 is a strap ring, 29 is an output part, 29a is an antenna feeder, 30 , 30 is a pair of pole pieces, 31
are cathode input section insulating cylinders 32 and 33 are cathode supports, 34 and 35 are cathode terminals, and 36
is a chiyoke coil, 37 is a feedthrough capacitor,
37a represents a cathode input terminal, and 38 represents a shield box. In this way, a voltage of several thousand volts is applied between the anode vane 26 and the cathode 25, and a magnetic field is applied to the electron action space 39 by the magnet in a direction parallel to the cathode axis, that is, the tube axis, causing oscillation. Most of the oscillated microwaves are supplied from the output section 29 to the external load through the antenna feeder 29a. The microwave power output from the output section 29 contains some noise other than the fundamental wave, but on the other hand, the cathode terminal 34,
Unnecessary high frequency noise leaks through a filter circuit consisting of a filter circuit 35, a choke coil 36 and a capacitor 37 connected thereto and forming part of the input conductor. This noise component is distributed from several tens of Hz to several GHz. Of course, the filter circuit attenuates the noise power leaking toward the power transformer and commercial power line, but in order to fully achieve this leakage suppression effect,
A fairly sophisticated filter circuit must be used. By the way, when we measured the noise components leaking in the direction of the input line using the measurement circuit shown in Fig. 2 for a magnetron with the structure shown in Fig. 1, we found that the noise in the frequency components up to around 1000 MHz was almost the same as shown in Fig. 3. A continuously distributed spectrum is detected. However, in this case, the measurement results are obtained when the filter circuit shown in FIG. 1, that is, the choke coil and capacitor are not used. In addition, in Fig. 2, the symbol 2
0 is the magnetron to be measured as shown in Fig. 1, 4
0 is a waveguide, 41 is a dummy load, 42 is a cathode power supply, 43 is a high voltage power supply, 44 is a cathode input line, 45 is a measurement probe such as a ferrite clamp, and 46 is a spectrum analyzer. Now, one of the causes of such continuously distributed magnetron noise can be estimated as follows. In other words, Figure 4 schematically shows the coaxially arranged anode and cathode of a magnetron. In the figure, the cathode is negative and the anode is positive, and a high voltage of several 1000 (V) is generated between the cathode and the anode. When thermionic electrons are emitted from the cathode, the potential distribution in the action space 39 becomes concave downward as shown by the dotted curve a in the figure due to the space charge near the cathode. On the other hand, as shown by arrow B, this action space has
Since a DC magnetic field of 1000 to 2000 Gauss is applied in the axial direction of the cathode, the electrons leaving the cathode orbit around the cathode due to the action of the electric and magnetic fields. In particular, due to the orthogonal electromagnetic field, the traveling distance of the electrons is long, so there is a high probability that the electrons will collide with residual gas, and significantly more positive ions () are generated than in other straight tubes. The generated positive ions flow into the valley of the potential distribution shown by curve a (indicated by symbol m in the figure), and the electrons and positive ions in the space charge field gradually become neutralized, and as a result, the area near this valley The potential increases to a potential equal to or slightly higher than that of the cathode 25, as indicated by the symbol m. In this state, the potential distribution in the working space becomes like a solid line curve b. In the next step, a potential valley m is again formed by space charges. This series of processes is repeated periodically. As a result, a complicated pulsation phenomenon occurs in the current between the cathode and the anode, that is, the anode current, and it can be assumed that this leaks into the external circuit as noise. Therefore, it is considered that the noise generated in this way forms a relatively low frequency component of, for example, 1000 MHz or less. Such noise components mainly appear as so-called line noise that leaks along the input line. Furthermore, such noise causes various kinds of radio wave interference. Based on the above reasoning about the causes of noise generation, in order to reduce such noise components, it is necessary to substantially eliminate the valleys in the potential distribution that occur in the electron action space, especially near the cathode, or to It is considered that the configuration should be such that unstable fluctuations near the valleys of the potential distribution can be eliminated by removing stray positive ions without delay. Therefore, in order to suppress the generation of this kind of electron tube noise, the present inventors have proposed placing a third electrode, that is, a drain electrode, which provides the same potential or a negative potential as the cathode near the cathode (patent application
55-130762). Basically, the present invention suppresses the generation of relatively low frequency component noise by arranging a third electrode near the cathode, similar to the above proposal, and in particular, this invention has been completed to a practical configuration. It is something that
In other words, if you try to mechanically hold the third electrode near the cathode with an insulating object such as ceramic, the extremely high temperature near the cathode will lead to the generation of gas, and it will not be possible to sufficiently suppress noise caused by ions. It has been found that there are inconveniences caused by not doing so. Therefore, in the present invention, the third electrode is left in a free end state without using an insulator in the vicinity of the cathode, and the third electrode is constructed using a cylindrical base body in the vicinity of the cathode, and the third electrode is placed at a sufficient distance from the cathode. It is designed to be mechanically held at or near the cathode stem via an insulator. Examples thereof will be described below with reference to the drawings. Note that the same parts are represented by the same symbols. The magnetron of the embodiment shown in FIGS. 5 and 6 has the following configuration. The figure shows only the main body of the magnetron oscillator, and the radiator, magnetic circuit, shield box, filter circuit, etc.
Assembled as shown. To explain the cathode structure in detail, an end hat 51a and an end tip 52 are fixed to one end of a rod-shaped cathode support 32 arranged on the tube axis, and the other end of the cathode support is connected to a cathode terminal 35 and an exhaust pipe. 54. One end of the sleeve-shaped cathode support 33 is insulated by a ceramic spacer 55 and coaxially arranged and joined to the end hat 51b, and the other end is connected to another cathode terminal 3.
It is joined to 4. A thorium tungsten directly heated cathode 25 wound into a coil is connected between the end chip 52 and the end hat 51b. Thereby, the cathode 25 can be electrically heated by the heating power supplied to the cathode terminals 34 and 35. Now, inside the sleeve-like cathode support 33, a sleeve-like support 57 for a third electrode is coaxially disposed in an insulated manner, and is connected to a third electrode terminal 58 that is hermetically sealed to the upper end of the insulating cylinder 31. combined. And insulating tubes 31, 31a, 31b
A third electrode 60 is provided at the lower end of a third electrode support 57 fixed to the input stem section.
Therefore, in the third electrode 60 , a conductive cylindrical base 61 smaller than the inner diameter of the cathode spiral is provided inside the cathode 25, and a spiral protruding piece 62 is provided on the outer periphery of the base 61 and protrudes between each spiral of the cathode.
are integrally provided. And this base 61
The lower end 61a is left as a free end without intervening an insulator or the like, and a ceramic insulator 63 connects the inner rod-shaped cathode support 32 at a position above the end hat 51b in the figure, that is, above the pole piece 30. The other end is joined to a third electrode support 57 which is tightly fitted into the center hole of the third electrode terminal 58 and mechanically held.
In this way, the third electrode 60 is held on the cathode support via the insulator at a position sufficiently away from the cathode 25, and its tip remains free. Further, the third electrode 60 has a protruding piece 62 formed between the spirals of the cathode 25 and protruding to a position equivalent to the outer periphery of the cathode. Also this third
The electrode is preferably made of a single substance or an alloy selected from refractory metals such as W, Mo, Ta, and Ti, and is preferably formed in a surface condition that does not emit primary or secondary electrons, as shown in the figure. It is placed near the cathode and in a position that does not impede the flow of electrons from the cathode to the anode. As an example
It is a magnetron with an output of approximately 800 (W) in the 2.45 GHz band, the cathode coil wire diameter is 0.58 mm, the pitch spacing of the cathode and third electrode protruding pieces is 2.0 mm, the outer diameter of the spiral is 5.0 mm, and the anode The inner diameter of the vane tip is 10mm. Therefore, the outer peripheral surfaces of the cathode spiral and the third electrode spiral are on the same plane with a distance of 1 mm.
Arranged alternately at intervals. In addition, the code 31 in the figure
a and 31b represent ceramic insulating tubes. Further, the anode vane 26 and the anode cylinder constitute a plurality of cavity resonators, and together form an anode. The magnetron 20 according to the embodiment of the present invention having the above structure is operated by being connected to the power supply circuit shown in FIG. In the figure, reference numeral 71 is a leakage transformer whose primary side is connected to a commercial power supply and whose secondary side is wound with a high voltage winding 71a, a cathode heating winding 71b, and a third electrode power supply winding 71c, and 72 is a leakage transformer of about 0.5 μF. A paper capacitor, 73 a high-voltage rectifier diode, and 74 a power rectifier circuit for applying a potential between the cathode and the third electrode. Next, to explain the operation, the cathode is heated and emits thermoelectrons. A high voltage of several thousand (V) is applied between the cathode and the anode vane,
In addition, a DC magnetic field of approximately 1500 Gauss of magnetic flux parallel to the tube axis is applied to the electron action space, causing oscillation. The microwave energy generated in the cavity resonator is transmitted from the output section to the external load through the antenna feeder. Now, when the cathode is heated, a potential valley is formed in the vicinity of several tens of micrometers to several hundred micrometers in front of the cathode as shown in Figure 4 due to the emitted electrons (if there is no third electrode). For example, if the potential is set to a negative potential of about -100 to -500V, the positive ions that gather around the valley of the potential will be immediately captured by the third electrode because the potential is even more negative than this. .
That is, the positive ions do not remain in the vicinity of the cathode but flow into the third electrode, and the unstable electron-ion neutralization phenomenon in the vicinity of the cathode does not occur. As a result, the generation of noise, especially on the order of 1000 MHz or less, is reliably suppressed. In particular, according to the present invention, the third electrode is constituted by a cylindrical base and a protruding piece provided on the outer periphery of the cylindrical base,
This is mechanically independent or held via an insulator at a position away from the cathode, and the cathode has a free end structure without an insulator in the vicinity of the electron emitting portion of the cathode. Even if the temperature reaches a high temperature, there is no insulating material holding the third electrode in the vicinity, so gas release does not occur, and unstable operation and noise generation can be reliably suppressed. Moreover, if the third electrode is kept at a negative potential, this third electrode
Back bombardment of electrons to the electrode is also suppressed, and gas emission from the third electrode itself is less likely to occur. In this way, according to the present invention, stable operation is maintained. Note that even if the third electrode has the same potential as the cathode, a sufficient noise suppression effect can be obtained for practical use. As shown in FIG. 8, the main part of the third electrode 60 is made by winding a band-shaped body 81 having a protruding piece 62 around the outer periphery of a base body 61 made of a rolled conductive thin plate at the same pitch as a coiled cathode (not shown). It may be fixed. According to this, manufacturing is easy. Further, as shown in FIG. 9, a portion of the cylindrical base body 61 is cut and raised to form protruding pieces 6 arranged substantially in a spiral shape.
2, 62... may be formed. Furthermore, the embodiment shown in FIG. 10 has a third electrode 60 in which a conductive coil 82 is wound and fixed around the outer periphery of a cylindrical base 61 made of Mo or Fe and whose outer diameter is smaller than the inner diameter of the cathode 25.
The coil 82 forms the main part of the third electrode 60 , and its outer diameter is set larger than the inner diameter of the cathode 25. The embodiment shown in FIG.
A cylindrical third electrode 60 having a spiral concave portion 83 and a convex portion 84 having a shape and pitch corresponding to the spiral of the cathode is provided inside the electrode 5 . Also the 12th
In the embodiment shown in the figure, a coil 82 wound at the same pitch as the cathode is provided around the outer periphery of a cylindrical base 61, and both ends 82a, 82b of this third electrode coil 82 are fixed to the base 61. In each of these embodiments, the cylindrical base 61
The cathode stem is made to stand on a cathode stem having an insulating tube at a position away from the cathode, or is held on a cathode support via an insulator, and the tip of the cathode portion remains free. In the embodiment shown in FIGS. 5 and 6, the third electrode support 57 and the cylindrical base 61 were constructed separately, but in the other embodiments, the third electrode support 57 and the cylindrical base 61 were constructed separately. A case is shown in which the cylindrical base bodies 61 and 83 are integrated. As described above, the magnetron of the present invention stabilizes the operation of the third electrode for noise suppression and is highly practical.

[Brief explanation of the drawing]

Figure 1 is a vertical cross-sectional view showing the general structure of a magnetron, Figure 2 is a schematic diagram showing a noise measurement circuit, Figure 3 is a characteristic diagram of the input line noise generated from the magnetron, and Figure 4 explains its causes. Schematic diagram, 5th
The figure is a vertical cross-sectional view of main parts showing one embodiment of the present invention.
The figure is an enlarged view of the main parts, Figure 7 is an operating circuit diagram, and Figure 8 is an enlarged view of the main parts.
12 through 12 are longitudinal cross-sectional views of main parts showing other embodiments of the present invention. 25... Cathode, 26... Anode (Vane),
39...Electron action space, 60 ...Third electrode, 61...Cylindrical base, 62...Protrusion piece, 63...Insulator.

Claims (1)

[Claims] 1. A pair of cathode supports 32 supported by an input stem portion consisting of insulating cylinders 31, 31a, and 31b,
A pair of end hats 51a, 51 at the tip of 33
b is fixed, a spiral cathode 25 is connected between these end hats, and an anode vane 2 constituting a cavity resonator coaxially around this cathode.
6 is arranged, and a magnetic field parallel to the cathode axis is applied to the electron action space 39 between the cathode and the anode vane .
is provided to be electrically insulated from the cathode, and the third electrode 60 has conductive cylindrical bases 61 and 83 coaxially provided inside the cathode and having an outer diameter smaller than the inner diameter of the cathode. At the same time, spiral protruding members 62, 82, 84 located between the spirals of the cathode are fixed to the outer periphery of the cylindrical base, and the cylindrical bases 61, 83 are connected to the cylindrical base 61,
A magnetron characterized in that the magnetron is fixedly held on the input stem portion through a third electrode support 57 that is either integrated with the third electrode support 83 or separate from the third electrode support 57 .