JP4326920B2 - Magnetron - Google Patents

Description

  The present invention relates to a magnetron that oscillates microwaves. More specifically, the present invention relates to a magnetron having a structure with improved frequency characteristics, in which the oscillation frequency does not change much even with the temperature rise due to the usage environment and its own heat generation.

  In recent years, there is a tendency for spurious emission regulations to become stricter for devices that emit microwaves. In this trend, regulations on radiation near the fundamental oscillation frequency of pulsed magnetrons are becoming stricter. Since the magnetron used in the radar performs a pulse operation, the spectrum of its oscillation output has many lobes in the sideband in addition to the main lobe, and has the characteristics shown in FIG. This spectrum characteristic is substantially determined by the output pulse width of the magnetron, and the bandwidth increases as the short pulse is reached. In order to suppress this increased occupied bandwidth, a method of attaching a filter or the like is employed.

A conventional magnetron is provided with a plurality of vanes 12 extending radially toward the center on the inner peripheral wall of a cylindrical anode shell 11 as shown in FIG. The anode 1 is formed with a resonant cavity, and a cathode 2 is provided in a space surrounded by the tip of the vane 12. Every other vane 12 is provided with straps 13 that are connected to each other, and the phase of the resonance cavity surrounded by the vanes 12 is made to differ by π radians so as to easily oscillate in the π mode. Reference numeral 3 denotes a pole piece for concentrating the magnetic field in the working space between the tip of the vane 12 and the cathode 2. The oscillation frequency of a magnetron having this structure generally has a negative temperature characteristic that it decreases as the temperature rises (see, for example, Non-Patent Document 1), and the temperature of the environment in which the magnetron is installed and the heat generation of the magnetron itself. Since the anode temperature of the magnetron changes due to the temperature rise due to the above, the occupied frequency bandwidth P of the oscillation frequency is assumed to be 170 MHz as shown in FIG. 5 assuming that the environmental temperature is changed from −40 ° C. to 120 ° C., for example. It will be of a much wider range.
“Magnetron Characteristics”, e2v technologies, [searched on November 12, 2003], Internet <URL: http: //e2vtechnologies.com/education/mag_characteristics_nojs.htm>

  As described above, in the magnetron having the above-described structure, it is assumed that the ambient temperature range changes to about −40 to + 120 ° C. depending on the use environment. Therefore, in the environment, the temperature characteristic of the oscillation frequency is − If 0.15 MHz / ° C., the frequency fluctuates by 24 MHz. Therefore, even if a filter for suppressing the bandwidth of the oscillation spectrum is attached, there is a problem that the oscillation frequency fluctuates as the temperature rises, and a spectrum that falls within the bandwidth regulation value cannot be secured. On the other hand, if the frequency regulation due to the temperature rise is taken into consideration and the bandwidth regulation requirement is satisfied, the frequency bandwidth becomes a very wide range, and the filter performance must be greatly improved. is there.

  The present invention has been made to solve such a problem, and even if the environmental temperature to be used fluctuates, the fluctuation of the oscillation frequency is suppressed to be small, and the occupied frequency bandwidth is minimized. An object of the present invention is to provide a magnetron having a possible structure.

The magnetron according to the present invention includes an anode in which a plurality of vanes are provided radially on the inner peripheral wall of a cylindrical anode shell so as to form a resonance cavity between adjacent vanes, and a tip of the vane. In a magnetron having a cathode provided along the axial direction of the anode shell at a central portion of the anode shell surrounded, the magnetron has a fixed end with one end fixed to the inner peripheral wall of the anode shell, and the other end is a movable end become metal piece so as to face the resonant cavity set vignetting, the metal strip, as the coefficient of thermal expansion of the metal of the vane-side is smaller than the thermal expansion coefficient of the opposite side of the metal with the vane side, At least two kinds of metal pieces having different thermal expansion coefficients are joined, and at the time of temperature rise accompanying the operation of the magnetron, the warpage caused by the difference in the thermal expansion coefficient causes And which are located so as to suppress variations in oscillation frequency due to temperature close to the resonant cavity temperature.

  Here, the vane means a partition wall for partitioning individual anode resonance cavities, and not only a plate-like anode piece connected and fixed to a normal inner peripheral wall of the anode shell but also an anode shell such as a rising sun type. It also includes a partition wall between the small cavities in the case where a resonance cavity is formed by being divided into a plurality of small cavities by forming slits and slots in the single body.

  With this structure, the anode temperature during the operation of the magnetron changes due to changes in the environmental temperature, etc., for example, when the temperature rises higher than normal, the normal magnetron has the characteristic that the oscillation frequency decreases due to its negative temperature coefficient. However, in the magnetron of the present invention, a metal piece is provided on the axial end side of the vane constituting the resonance cavity, and the metal piece has a metal having a small thermal expansion coefficient on the resonance cavity side. The metal having a large expansion coefficient is joined so as to be opposite to the resonance cavity. For this reason, when the temperature rises, the metal piece warps to approach the resonant cavity. As a result, the metal piece approaches the resonance cavity, and the inductance L of the resonance cavity is reduced, and the oscillation frequency is increased. Then, both the negative temperature characteristic inherent in the magnetron and the action of the metal piece according to the present invention are offset, and the change in the oscillation frequency due to temperature hardly occurs. That is, when the temperature rises, the action of lowering the normal oscillation frequency cancels out the action of raising the oscillation frequency by the metal piece of the present invention, and the oscillation frequency does not change much even when the temperature rises. Even when the temperature is lowered, the frequency is simply changed in the opposite direction, which is canceled in the same manner, and fluctuations in the oscillation frequency can be suppressed.

  Since the above-mentioned metal piece is selected from the group consisting of Kovar, molybdenum, platinum, iron, nickel, gold, copper and silver, there is almost no gas emission even when placed in a vacuum tube, and a combination of thermal expansion coefficients. Therefore, the material can be selected according to the frequency change with respect to the temperature depending on the type of magnetron.

  Next, the magnetron of the present invention will be described with reference to the drawings. The magnetron according to the present invention is shown in FIGS. 1A to 1B as a longitudinal sectional view of an embodiment thereof and a bottom view of an anode portion thereof. A plurality of vanes 12 are provided radially toward the center, and a resonance cavity is formed between the adjacent vanes 12 to form the anode 1, and the center of the anode shell 11 surrounded by the tip of the vane 12. The cathode 2 is provided along the axial direction of the anode shell 11 at the part. A metal piece 5 connected to the anode shell 11 is provided so as to face the end of the vane 12 on the axial direction side.

  As shown in FIG. 1 (c), this metal piece 5 is formed by joining at least two kinds of first and second metal pieces 51 and 52, as shown in FIG. When the thermal expansion coefficient of the first metal piece 51 on the vane 12 side is made of a material smaller than the thermal expansion coefficient of the second metal piece 52 on the side opposite to the vane 12 side, Due to the warpage caused by the difference in thermal expansion coefficient between the first and second metal pieces 51, 52, the resonance cavity (vane 12) is approached and the fluctuation of the oscillation frequency due to the temperature of the anode 1 is suppressed. It is characterized by being.

  As shown in FIG. 1A, for example, the basic structure of the magnetron is fixed at one end to the inner peripheral wall of a cylindrical anode shell 11 made of oxygen-free copper, for example. A plurality of vanes (anode pieces) 12 are provided so that a tip portion opposed to the one end portion extends radially toward the center of the anode shell 11, thereby forming a plurality of resonant cavities between adjacent vanes 12. The anode resonance cavity is formed by the entirety of the plurality of resonance cavities to constitute the anode 1, and the cathode 2 is provided along the axial direction at the center of the anode shell 11. . Every other vane 12 is connected by a strap 13 so that the π radians have different phases, thereby forming a structure that facilitates π mode oscillation. A pair of pole pieces 3 made of iron or the like is provided so that a magnetic field substantially parallel to the cathode 2 can be applied to the working space in which the tip of the vane 12 and the cathode 2 face each other. It is configured to be. The electrons emitted from the cathode 2 are formed so as to be oscillated by bending the electrons by an electromagnetic field applied to the working space and giving the energy to the cavity by turning.

  In the example shown in FIG. 1, a magnetron having a vane structure in which a plurality of vanes are fixed to the inner peripheral wall of the anode shell to form a plurality of resonant cavities is shown. The present invention is similarly applied to the case where the small cavity partition is regarded as a vane even in the case of a plurality of small cavities formed by a slot formed integrally with the anode shell. Can be applied.

  In the example shown in FIG. 1, the metal piece 5 is formed on the inner peripheral wall of the anode shell 1 as shown in FIG. 1 (b), which is a bottom view with the pole piece 3 and the cathode 2 of FIG. 1 (a) removed. A ring-shaped plate-like body whose outer periphery is fixed is formed with a slit 5a along the circumference and a cutting portion 5b that cuts the continuity in the circumferential direction by bending the end of the slit 5a toward the inner circumference. Thus, a connecting portion 5c and a separating portion 5d with the anode shell 11 are formed. The separating portion 5d has one end portion 5e fixed to the anode shell 11 via the connecting portion 5c and the other end portion 5f being a free end. In the shape of an L ring. In the example shown in FIG. 1, four separation portions (L-rings) 5d are formed along the circumferential direction.

  As shown in FIG. 1 (c), a part of the metal piece 5 includes first and second metal pieces 51, 52 mainly at both ends of one end 5e and the other end 5f. It is joined with. The material of both metal pieces 51 and 52 is selected so that the first metal piece 51 on the vane 12 side has a smaller thermal expansion coefficient than the material of the second metal piece 52 on the opposite side to the vane 12 side. ing. The first and second metal pieces 51 and 52 may be joined on the entire surface, but it is sufficient that at least both ends of the one end portion 5e and the other end portion 5f are joined. That is, when the temperature rises, the metal pieces 51 and 52 having different thermal expansion coefficients are joined for the purpose of obtaining warpage based on the difference between the thermal expansion coefficients of the two metal pieces 51 and 52. Therefore, as shown in FIG. 1 (c), at least the part of the separation part 5d has only to be joined to the part where the first and second metal pieces 51 and 52 are joined, and the connecting part 5c is one side. The metal piece alone is preferred because it can be reliably fixed with a material having a small difference in thermal expansion coefficient from the anode shell 11. However, you may join both the metal pieces 51 and 52 also including the connection part 5c.

As described above, since the metal piece 5 is provided for the purpose of obtaining warpage when the temperature changes, the first and second metal pieces 51 and 52 have a thickness in consideration of the curvature. Is preferably within 0.5 mm, more preferably about 0.05 to 0.2 mm. The first and second metal pieces 51 and 52 need to use materials having different coefficients of thermal expansion. However, since the magnetron is a vacuum tube and the inside of the anode is at a high temperature, it can withstand the high temperature and emit gas. The material must be low. As a result of the study of the optimum material for the metal piece 5 by the present inventors, a material having a desired thermal expansion coefficient is selected from a material consisting of Kovar, molybdenum, oxygen-free copper, iron, gold, silver, nickel, and platinum. And found that it is preferable to combine them. Table 1 shows the linear expansion coefficients (× 10 ⁻⁶ / ° C.) of these materials at 20 ° C.

  In the example shown in FIG. 1, a 0.1 mm-thick Kovar plate is used as the first metal piece 51, and a 0.1 mm-thick oxygen-free copper plate is used as the second metal piece 52, and only the separation portion 5 d is used. The first metal piece 51 is bonded, and is bonded using a brazing material only at both ends of the one end 5e and the other end 5f. Note that the outer periphery of the connection portion 5 c of the metal piece 5 is fixed to the inner peripheral wall of the anode shell 11 with a brazing material or the like. As a result, the separating portion 5d has a fixed end in which one end portion 5e is fixed to the inner peripheral wall of the anode shell 11 via the connecting portion 5c, and an L-ring shape in which the other end portion 5f becomes a movable end in a free state. It has become.

  As described above, the first and second metal pieces 51 and 52 made of at least two kinds of metals having different thermal expansion coefficients are joined, and one end portion 5e is a fixed end and the other end portion 5f is a movable end. Therefore, for example, when the temperature rises, the first metal piece 51 has a small coefficient of thermal expansion, and the second metal piece 52 has a large coefficient of thermal expansion. Therefore, the second metal piece 52 has a larger expansion, and the metal piece 5 Bend to the first metal piece 51 side. That is, the metal piece 5 bends in a direction approaching the vane 12, in other words, the resonance cavity. As a result, the inductance of the resonance cavity is reduced, and the resonance frequency of the resonance cavity, in other words, the oscillation frequency of the magnetron is increased. In this metal piece 5, the greater the difference between the thermal expansion coefficients of the first and second metal pieces 51 and 52, the greater the distance (length M) between the fixed end 5e and the movable end 5f of the separating portion 5d. The bending of the metal piece 5 is so large that the vane 12 is easily approached. Then, the closer to the vane 12 is, the larger the area of the approaching metal piece 5 is, the higher the oscillation frequency is. On the other hand, when the temperature is lowered, the metal piece 5 bends away from the cavity resonator and performs the opposite action.

  In the example shown in FIG. 1, four separation parts 5 d having such an L-ring shape are attached to the inner wall of the anode shell 11. When the ring-shaped metal piece 5 shown in FIG. 1 is provided in an x-band (9 GHz band) magnetron, the inner diameter is about 18 mm (the width D of the separation part 5d is about 2 mm), and one separation part ( The length M of the L ring) 5d can be formed to about 10 mm. As described above, for example, Kovar is used as the first metal piece 51 and oxygen-free copper is used as the second metal piece 52, so that the length M of the L ring 5d is 10 mm as described above. At 100 ° C., the movable end will be bent by 0.25 mm. FIG. 3 shows the result of examining the relationship between the resonance frequencies when the distance between the movable end of the metal piece 5 having this shape and the end of the vane 12 (end in the axial direction) is changed. In FIG. 3, the vertical axis represents the change amount with the oscillation frequency when the distance between the movable end and the vane end is 2 mm as a reference (0).

  From FIG. 3, it can be seen that the change amount of the movable end of the separation part (L ring) 5d only needs to be 0.12 mm to change the frequency by 15 MHz. Since the drift amount of the oscillation frequency due to the temperature of the conventional magnetron is about −150 kHz / ° C., it drifts by 15 MHz at 100 ° C. However, as described above, the movable end of the metal piece 5 changes by 0.12 mm. By doing so, temperature compensation for a temperature change of 100 ° C. can be performed. As a result, according to the above-described configuration, since it can be bent by 0.25 mm at 100 ° C., the necessary temperature compensation range is covered, and the first metal piece 51 is made of platinum or iron having a larger thermal expansion coefficient than Kovar. The first metal piece 51 is used as Kovar or Molybdenum, and the frequency change corresponding to the drift of the magnetron is adjusted by reducing the width D of the separation part 5d or shortening the length M. can do. If the length M is shortened, not only will the amount of bending be reduced, but even if the distance between the movable end and the vane is the same, the contribution to the change in oscillation frequency will also change. become.

  In the above-mentioned structure, the length M is adjusted to 8 mm, and in other cases, the anode outer wall temperature of the magnetron manufactured by the above-described structure and material examples is changed by changing the environmental temperature, and the change of the oscillation frequency at that time is examined. It was. As shown in FIG. 4 as the result of the present invention, the oscillation frequency changes only by about 2 MHz even when the temperature is changed from −40 ° C. to 120 ° C., whereas a similar change in the oscillation frequency due to the magnetron having the conventional structure. As shown in FIG. 4 in contrast to the conventional structure, the bandwidth changes by about 24 MHz, and the bandwidth occupied by about 22 MHz can be narrowed.

  In the above example, by forming a slit in the metal ring having a structure in which the metal piece 5 can be fixed to the inner peripheral wall of the anode shell, the connecting portion 5c and the separating portion 5d are formed, and the bending of the L-ring shaped separating portion 5d is performed. However, as shown in FIG. 2A, for example, it may be formed directly as an L-ring-shaped metal piece 5, and the bottom side of L may be directly fixed to the inner peripheral wall of the anode shell. Further, the length and width can be freely set, and a desired temperature coefficient can be canceled by adjusting the number (not limited to four), the length, the width, and the like. Such an L-ring shape is preferable because the distance between the fixed end and the movable end can be increased, and the amount of change due to bending can be increased. It is not limited to the L ring shape.

The example shown in FIG. 2 (b) is similar to FIG. 1 (b), and the direction of the fixed end 5e and the movable end 5f is not the circumferential direction of the anode shell 11 but the radial direction. This is an example. That is, the fixed end 5 e side is fixed to the anode shell 11 throughout, and the movable end 5 f is formed so as to protrude to the center side of the anode shell 11. By forming in this way, the distance N between the fixed end 5e and the movable end 5f is small, so the distance approaching the vane 12 side is small, but the heat is applied to the first metal piece 51 and the second metal piece 52. By using a material with a large difference in expansion coefficient, increasing its width (N), or increasing the area approached by providing it in the majority of the circumferential direction, it is possible to obtain bending due to temperature changes. Since the interval can be changed over a wide area, the oscillation frequency drift can be sufficiently compensated. Further, in this case, since the metal piece 5 can be brought relatively close to each small cavity (resonant cavity sandwiched between vanes), stable frequency characteristics can be obtained.

  In the case of this example as well, the fixing part to the anode shell 11 may be only the second metal piece or the first metal piece, and the first and second metal pieces may be joined at other parts. .

  The variable temperature compensation amount described above is a function of how much the reactance of the magnetron resonance cavity is changed by temperature. Therefore, the temperature compensation amount can be appropriately selected by changing the arrangement of the metal pieces under the above-described configuration, and depending on the type of magnetron (the degree of frequency fluctuation varies depending on the structure) The thickness, length, size, combination of materials, and the like of the pieces can be set as appropriate. Moreover, in order to increase the effect, the shape of the dissimilar metal piece can be devised, and it is not necessarily required to be divided into four as in the above-described embodiment. Further, the effect can be further increased by devising such as providing a protrusion on the movable end side.

  Furthermore, in each of the above-described examples, the dissimilar metal is composed of only the first and second metal pieces, but three or more kinds of metal pieces may be joined. In the above example, the metal piece 5 is provided only on the side of the vane 12 where the strap 13 is not provided. However, the metal piece 5 may be provided on either side regardless of the presence or absence of the strap. It may be provided on the side. The strap 12 is not limited to the example shown in FIG. 1, and may be provided at both end portions of the vane 12.

It is a figure explaining one Embodiment of the magnetron by this invention. It is explanatory drawing which shows the modification of the metal piece of FIG. It is a figure which shows the relationship of the frequency change with respect to the distance of the movable end of a metal piece, and a vane by the structure shown by FIG. It is a figure which shows the relationship of the change of the oscillation frequency with respect to the change of the anode outer wall temperature of a magnetron. It is the figure which showed the spectrum waveform by the conventional magnetron in both the case where the outer wall temperature of an anode is -40 degreeC and 120 degreeC. It is structure explanatory drawing of the conventional magnetron.

Explanation of symbols

1 Anode 2 Cathode 3 Pole Piece 5 Metal Piece 11 Anode Shell 12 Vane 13 Strap 51 First Metal Piece 52 Second Metal Piece

Claims (1)

A plurality of vanes are provided radially on the inner peripheral wall of the cylindrical anode shell so as to form a resonance cavity between adjacent vanes, and the anode shell surrounded by the tip of the vane In a magnetron having a cathode provided along the axial direction of the anode shell at the center , a metal piece having one end fixed to the inner peripheral wall of the anode shell and a metal piece having the other end serving as a movable end set to face the resonant cavity vignetting, the metal strip, as the coefficient of thermal expansion of the metal of the vane-side is smaller than the thermal expansion coefficient of the opposite side of the metal with the vane side, differ by at least thermal expansion coefficient It consists of two kinds of metal pieces joined together, and at the time of temperature rise due to the operation of the magnetron, due to warpage due to the difference in thermal expansion coefficient, Magnetron, characterized in that is provided so as to suppress the fluctuation of the oscillation frequency.

Images