JPS6231776B2 - - Google Patents

Description

[Detailed description of the invention] The present invention relates to an orthogonal electromagnetic field type electron tube.

Orthogonal electromagnetic field type electron tubes that obtain high frequency oscillation and power amplification by applying a magnetic field in a direction perpendicular or nearly perpendicular to the direction of electron movement are known as magnetrons, magnetron-type traveling wave tubes, and other similar electron tubes. It has come into practical use as a Electronic devices equipped with this, such as microwave ovens, are now widely used, and as a result, regulations regarding noise leakage have become stricter. Internationally, standards by the International Special Committee on Radio Interference (CISPR) have been implemented or are being considered for implementation in various countries regarding this noise regulation. Therefore, for this type of electron tube, there is a need for measures to further reduce noise emitted from the electron tube itself, radiation of unnecessary radio waves, and leakage.

The conventional structure and noise generation situation will be explained below using a magnetron as an example. For example, the structure of a 2.45 GHz microwave oven magnetron is shown in Figure 1. In the figure, 21 is the main body of the magnetron oscillation unit, 22 is the radiator, 23 and 23 are the ferrite magnets, 24 is the yoke, 25 is the directly heated cathode wound in a coil, 26 is the anode vane, and 27 is the anode cylinder. , 28 is a strap ring, 29 is an output section, 29a is an antenna feeder, 30, 30 are a pair of pole pieces, 3
1 is the cathode input section insulation cylinder, 32, 33
is a cathode support, 34 and 35 are cathode terminals,
36 is a chain coil, 37 is a feedthrough capacitor, 37a is a cathode input terminal, and 38 is a shield box. In this way, there are several thousand () between the anode vane 26 and the cathode 25.
voltage is applied, and a magnetic flux in a direction parallel to the cathode axis, that is, the tube axis, is applied to the electron action space 39 by the magnet, causing oscillation. Most of the oscillated microwaves are supplied from the output section to the external load through the antenna feeder. The microwave power emitted from the output section contains quite a bit of noise other than the fundamental wave, but on the other hand, unnecessary high-frequency noise is removed through the filter circuit consisting of the cathode terminal and the chiyoke coil and capacitor that are connected to this and form part of the input conductor. Noise leaks. This noise component is several 10Hz
It is distributed over several GHz. Of course, the filter circuit attenuates the noise power that leaks into the power transformer and the commercial power line, but in order to achieve this leakage suppression effect completely, a fairly high-grade filter circuit must be used.

By the way, when we measured the noise component leaking in the input line direction of the magnetron having the structure shown in Fig. 1 using the measurement circuit shown in Fig. 2, we found that there was almost no noise in the frequency component up to around 1000 MHz, 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.

The present invention aims to suppress the generation of noise as described above. In other words, in order to cope with the remarkable ionization of residual gas in the tube, which is inevitable in orthogonal electromagnetic field type electron tubes, a drain electrode is provided near the cathode to collect the positive ions, and this electrode is placed at the same potential as the cathode. Alternatively, the potential is set to be negative with respect to the cathode, and potential fluctuations in the working space near the cathode are suppressed, thereby suppressing the generation of noise.

Examples of the magnetron will be described below with reference to the drawings. Note that the same parts are represented by the same symbols.

In the embodiments shown in FIGS. 5 and 6, only the main body of the magnetron oscillation section is shown, and the radiator, magnetic circuit, shield box, filter circuit, etc. are assembled in the same manner as in FIG. To explain the cathode structure in detail, an end hat 51a, a ceramic insulator 52, and a conductive block 53 are attached to one end of a rod-shaped cathode support 32 arranged on the tube axis.
are fixed in sequence, and the other end of this cathode support is joined to the cathode terminal 35 and the exhaust pipe 54. The sleeve-shaped cathode support 33 has one end thereof insulated by a ceramic spacer 55 and coaxially arranged and joined to a stepped cylindrical part 56, and the other end joined to another cathode terminal 34. A thorium tungsten directly heated cathode 25 wound into a coil is connected between the cylindrical part 56 and the conductive block 53. This causes the cathode 25 to connect to the cathode terminals 34, 35.
It is designed so that it can be electrically heated with the heating power supplied to it.

Now, on the outside of the sleeve-like cathode support 33, a drain electrode sleeve-like support 57 is further insulated and coaxially disposed, and the insulating cylinder 3
Drain electrode terminal 58 hermetically sealed to the upper end of 1
is combined with This drain electrode support 57
A conductor sleeve 59 and an end hat 51b are connected to the lower end of the conductor sleeve 59, and one end of a drain electrode 60 wound in a coil is bonded and fixed to the sleeve 59. The drain electrode 60 is wound with the same pitch and helical diameter as the cathode 25,
The other end is mechanically held on the outer periphery of the ceramic insulator 52, for example by soldering or mechanical fitting, and is electrically terminated and floating at this portion. This drain electrode 60 is made of W, Mo, Ta, Ti.
A single substance or alloy selected from poorly soluble metals such as metals, formed in a surface condition that does not emit primary or secondary electrons, and as shown in the figure, near the cathode and from the cathode to the anode. It is placed in a position that does not impede the flow of electrons.
As an example, in a magnetron with an output of about 800 (W) in the 2.45 GHz band, the coil wire diameter of the cathode and drain electrodes are each 0.58 mm in diameter, the pitch interval of 0.5 mm is the same for both, 2.0 mm, the helical diameter is 5.0 mm, and the anode The inner diameter of the vane tip is 10mm. Therefore, the cathode spirals and the drain electrode spirals are arranged alternately at 1 mm intervals on the same plane. In addition, code 3 in the figure
1a 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, numeral 61 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 61a and a cathode heating winding 61b, 62 is a paper capacitor of about 0.5 μF, and 63 is a high voltage rectifier diode. , 64 represents a power source for applying a potential between the cathode and the drain 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, the emitted electrons form a potential valley near the cathode as shown in Figure 4 (when there is no drain electrode).
However, if the drain electrode is connected to the cathode, for example -
When the potential is set to a negative potential of about 200V, the positive ions that gather around the valleys of the potential are immediately captured by the drain electrode, which has an even more negative potential than this. In other words, positive ions do not stay near the cathode but flow into the drain electrode, and the unstable electrons near the cathode.
No ion neutralization phenomenon occurs. As a result, especially
The generation of noise on the order of 1000MHz or less is reliably suppressed.

In fact, as a result of measuring the noise level of a magnetron having the structure shown in FIGS. 5 and 6 using a measurement circuit similar to that shown in FIG. 2, the inventors obtained data that supports the above inference. Ta. This is shown in FIG. In FIG. 8, the appearance of the maximum value of the noise frequency component in the range of 0 to 100 MHz is graphed as a result of changing the voltage of the drain electrode with respect to the cathode. According to this measured value, compared to when the potential of the drain electrode is set to 0 (V), that is, the same potential as the cathode, the maximum noise value can be reduced by about 30 dB by reducing the potential of the drain electrode to about -150 (V) or less. . Furthermore, when a commercially available microwave oven is equipped with a magnetron and operated, the noise level emitted to the input line side was measured, and the results are shown in Figure 9. In other words, this data is expressed as a curve connecting the peak values of the spectrum below 100 MHz, but in contrast to curve 71 for the magnetron with the conventional structure shown in FIG. When set to -150V, as shown by curve 72, it can be seen that the reduction is approximately 20 dB in almost the entire frequency component range. As described above, the remarkable effects of the present invention are extremely clear. Therefore, there is a possibility of omitting the expensive line filter that is currently installed in many magnetrons and microwave ovens.

Further, in the present invention, even if the potential of the drain electrode is set to a negative potential with respect to the cathode, for example, about -200V, the current between the cathode and the anode, that is, the anode current hardly decreases. It has been found that when the coiled cathode and drain electrodes have the same helical diameter and are arranged on the same surface as in the above embodiment, the anode current slightly increases when the drain electrode is made negative.

In this respect, the present invention is essentially different from known electron tubes such as so-called gridded magnetrons for output control. In other words, an example of a magnetron with a control grid installed near the cathode can be found in the European book "Crossed Electromagnetic Field Microwave Device" (edited by E. OKRESS, "CROSSED-FIELD
"MICROWAVE DEVICES" Vol., 1961), especially the one with a grid for output power control as shown in Figure 2 on page 85 and its explanation, and the Japanese book "Research on ultra-high frequency magnetrons" (Tomonaga and Kotani eds., 1952). , Misuzu Shobo), there is a description of a magnetron with a lattice, etc., disclosed on pages 293 onwards. The former is aimed at varying the output power, while the latter measures noise using a triode, and states that there is essentially no difference in noise generation even if the grid voltage is changed. There is. In other words, in the case of a grid that controls the output power, in order to control the electron flow from the cathode, the cathode is placed so as to be virtually parallel to the anode vane, and it is placed a width apart from the cathode. be. Therefore, this is essentially different from the case of the present invention, which plays a role as a drain electrode for collecting and discharging positive ions flowing very close to the cathode.

The embodiment shown in FIG.
5 has a spiral cross-sectional shape that is flat in a direction parallel to the cathode axis, that is, the tube axis c. Further, the drain electrode 60 protrudes slightly toward the anode 26 than the cathode 25, and is located between each spiral of the cathode. In this example,
The potential of the drain electrode is the same as that of the cathode, but the potential is slightly negative. For example, even when the voltage is -150 (V), the decrease in the anode current should be kept at about 10% or less. As a result, even if the potential of the drain electrode is set to be the same as that of the cathode, a positive ion collecting action can be obtained, and a noise reduction effect can be obtained. Note that when the drain electrode and the cathode are to have the same potential, it is preferable to electrically connect the two through a high resistance.

The embodiment shown in FIG.
5, a cylindrical drain electrode 60 having a spiral recess 81 with a shape and pitch corresponding to the spiral.
are arranged close to each other. Note that the recess 8
Instead of forming a conductive cylinder 1, a simple conductive cylinder may be placed near the inside of the coiled cathode and a negative potential applied thereto.

Furthermore, in each of the above embodiments, the structure is such that the cathode and drain electrode are made separately and assembled insulated from each other, but the structure is not limited to this, and for example, the coiled cathode and the coiled drain electrode may be alternately arranged, or A plurality of spirals may be wound at intervals and electrically connected within the tube to have the same potential. Alternatively, an electron emitting layer may be deposited on the surface of every other spiral of a single coiled tigsten wire, and the remaining surface may be left in a surface state that makes it difficult for electrons to be emitted. The same operation can be obtained as with the alternating arrangement of cathodes and drains, that is, non-electron emitting surfaces, which are at the same potential. Furthermore, using a single piece of tungsten wire, a part of its surface is coated with an electron emitter, the rest of the surface is in a non-emissive state, and this is wound into a coil to serve as an electron emitting surface and a non-electronic wire that essentially becomes a drain electrode. The emitting surfaces may both be formed facing towards the anode. Also in this case, it is more effective if the non-electron emitting surface is configured to slightly protrude toward the anode. These devices are extremely easy to manufacture, are reliable in collecting positive ions, and suppress noise generation.

Next, a practical power supply circuit for applying a negative potential to the drain electrode will be described.

As shown in FIG. 12, the leakage transformer 61
An intermediate tap P1 is provided in the high voltage secondary winding 61a of
A voltage doubler rectifier circuit consisting of a capacitor 62 and a diode 63 is connected to this tap, and a winding 61c connected to the terminal 58 of the drain electrode is wound around the same transformer 61. As a result, a negative pulsating voltage is applied to the drain electrode during the half cycle in which the anode is at a high positive voltage with respect to the cathode. As a result, a relatively simple power supply circuit configuration is obtained. Further, a diode 82 may be connected as shown in FIG. 13, and a potential may be applied to the drain electrode by a voltage doubler rectifier circuit including a capacitor 83 and a diode 84 as shown in FIG. Furthermore, as shown in FIG. 15, a resistor R is connected between the cathode and the drain electrode, and a high voltage is applied between the drain electrode and the anode. may be given to Further, as shown in FIG. 16, the transformer 61 is provided with a secondary winding 61d for drain electrode power supply,
Drain electrode terminal 58 via full-wave rectifier circuit 85
A negative potential may be applied to the cathode. Alternatively, as shown in FIG. 17, a high voltage generated by a full-wave voltage doubler rectifier circuit and a drain electrode voltage rectifier circuit including a winding 61c, a diode 82, and a capacitor 86 may be combined.

In the structure shown in FIG. 18, a small transformer 86 and a voltage doubler rectifier circuit 87 for the drain electrode on the secondary side are arranged inside a shield box 38 of a magnetron so as to be insulated from the box. The primary side of the transformer is connected to the cathode input line. When a voltage of approximately 3V is applied to the cathode, the secondary side of the transformer 86 is several 10
It is sufficient if a voltage of about 100 (V) can be obtained. According to this embodiment, the power source for the drain electrode is built into the magnetron itself, so there is no need to change the power source device such as the leakage transformer 61 at all. Since the current flowing through the drain electrode is extremely small, the power supply circuit can be made sufficiently small, making it highly practical.

[Brief explanation of the drawing]

Fig. 1 is a vertical cross-sectional view showing the general structure of a magnetron as an example of an orthogonal electromagnetic field type electron tube, Fig. 2 is a schematic diagram showing a noise measurement circuit, Fig. 3 is a characteristic diagram of input line noise generated from the magnetron, FIG. 4 is a schematic diagram explaining the cause, FIG. 5 is a vertical sectional view of the main part showing an embodiment of the present invention, FIG. 6 is an enlarged view of the main part, FIG. 7 is an operating circuit diagram, and FIG. 10 and 11 are longitudinal sectional views of main parts showing other embodiments of the present invention, and FIGS. 12 to 18 each show examples of operating circuits. FIG. 25... Cathode, 26... Anode (Vane),
39...Electron action space, 60...Drain electrode, 64
...Drain electrode power supply.

Claims (1)

[Scope of Claims] 1. A directly heated cathode spirally wound using a poorly soluble metal as a base, an anode with a built-in cavity resonator coaxially arranged around this cathode, and a space between these cathodes and anodes. In an orthogonal electromagnetic field type electron tube comprising, in an electron action space, a magnet that provides a magnetic flux substantially parallel to the cathode axis, a drain electrode is located between the spirals of the cathode without contacting the spirals, and the drain electrode 1. An orthogonal electromagnetic field type electron tube, characterized in that the electrode is configured to be able to apply a potential that is the same as or negative to the cathode potential. 2. The orthogonal electromagnetic field type electron tube according to claim 1, wherein the drain electrode is made of a refractory metal spirally wound at the same pitch as the spirally wound cathode. 3. The orthogonal electromagnetic field type electron tube according to claim 1, wherein the drain electrode has an outer peripheral end thereof protruding toward the anode than an outer peripheral end of the cathode. 4. The orthogonal electromagnetic field type electron tube according to claim 1, wherein the drain electrode is made of a single element or an alloy selected from W, Mo, Ta, and Ti.