JP4909654B2 - Pulse magnetron - Google Patents

Description

  The present invention relates to a pulse magnetron that oscillates a microwave by a pulse operation. More specifically, the present invention relates to a pulse magnetron having a structure capable of effectively suppressing spurious oscillation.

  In the magnetron, for example, as shown in FIG. 6, a plurality of vanes 12 are provided radially on the inner periphery of a cylindrical anode shell 11, and the space between the two adjacent vanes and the anode shell 11 is empty. Since the body is formed and the strap 14 stabilizes the π-mode oscillation, the anode 1 is formed by connecting every other vane 12. A cathode 2 is arranged at the center of the anode 1, and a magnetic field substantially parallel to the surface of the cathode 2 can be applied to the working space 4 between the inner peripheral end (vane 12 tip) of the anode 1 and the surface of the cathode 2. In this way, a pair of pole pieces 3 are provided at both axial ends of the anode shell 11, and electrons emitted from the cathode 2 rotate in the action space 4 by the action of orthogonal electromagnetic fields to give energy to the cavity. It is structured to oscillate. A magnetron used in a radar or the like can be operated by applying an anode voltage in pulses.

  In recent years, there is a tendency for spurious emission regulations to become stricter for devices that emit microwaves. In this trend, spurious at frequencies near the fundamental oscillation frequency of the pulse magnetron is becoming a problem. Since the magnetron used in the radar operates with pulses, the spectrum of the oscillation output has a waveform having lobes in the side bands in addition to the main lobe, as shown in FIG. This spectrum characteristic is determined by the pulse width for operating the pulse magnetron, and is not narrower than the spectrum obtained by Fourier analysis based on the oscillation output waveform. On the other hand, it usually spreads more than the theoretical spectrum described above due to various factors. In addition, a line-symmetric waveform is not shown centering on the fundamental oscillation frequency, and as shown in FIG. 7, there may be a distribution (P ′) protruding in the lobe of the side band, which causes spurious. ing.

  As described above, one of the causes of the spectrum collapse and the sideband lobe protruding is oscillation other than the rated operating point at the rise of the pulse magnetron. When the conventional pulse magnetron is oscillated, when the anode voltage is gradually increased, oscillation is already performed at a current value as low as about 5 to 10% of the rated current value for operating the pulse magnetron. The output level at this time is about −40 to −60 dBc of the rated output, and the frequency is oscillated on the side lower than the fundamental wave oscillation frequency at the rated time. When a conventional magnetron having such operating characteristics is used in pulse operation, it passes through this current region every time the pulse rises on the lower fundamental frequency side, so that the rated output of -40 to- Oscillation of about 60 dBc is performed as indicated by Q ′ in FIG. Therefore, when the spectrum is observed, a distribution having protrusions of about −40 to −60 dBc in the side band on the lower side of the fundamental frequency is shown.

When such spurious radiation occurs, unnecessary radio waves are radiated from the radar set, which causes a problem. Therefore, it is necessary to mount a filter in the radar set. However, the radar set is often mounted at a high position on the ship and requires a lightweight and compact design, and the processing accuracy of the filter attenuates the fundamental wave while ensuring attenuation other than the fundamental wave. Therefore, there is a problem that the dimensional processing with very high accuracy is required and the cost is increased. Therefore, when the pulse magnetron is driven with a pulse, it is important to suppress oscillation immediately before the fundamental wave at the rising edge of the pulse oscillates at the fundamental wave frequency. In order to suppress oscillation other than the rated operating point due to the non-uniformity of the electric field distribution and magnetic field distribution in the working space, measures such as changing the distance between the cathode surface and the vane tip in the axial direction are taken. (For example, refer to Patent Document 1).

On the other hand, in the magnetron, the electrons emitted from the cathode, due to the action of the magnetic field described above, spirally move back to the cathode and reversely bombard the cathode (back bombardment). In order to prevent thermionic emission material from being exposed on the entire surface of the cathode, a mesh is provided on the cathode surface, and the electron emission material is embedded in the mesh, or the substrate metal of the cathode is formed with lattice-like irregularities or stripes And a structure in which an electron-emitting material is embedded in the recess, for example, as shown in FIG. 8, the groove is formed along the axial direction of the cathode base metal 21. The one in which 25 is formed is also known (see, for example, Patent Document 2).
Japanese Patent Application Laid-Open No. 2004-164989 JP 2000-299069 A

  As described above, since the electric field distribution and magnetic field distribution in the working space are made uneven due to the structure of the magnetron, the behavior of slight rising electrons causes spurious generation at a very low level. Measures to suppress oscillation other than the rated operating point have been taken.

  However, as a result of further intensive studies by the present inventors, it has been found that oscillations other than the rated operating point can occur and the same spurious can occur depending on the coating structure of the thermionic emission material on the cathode surface. Oscillations other than the rated operating point due to the electron emission material coating structure are the cathodes in which the electron emission material is embedded in the groove as shown in FIG. But I have found that this happens as well. As mentioned above, when oscillations other than the rated operating point occur, the oscillation spectrum collapses and the sideband lobe protrudes, and spurious emission with strict regulation occurs. Requested.

  The present invention has been made in view of such a situation, and prevents oscillation due to an operation lower than the rated operating point at the time of pulse rising or falling, which is particularly problematic in a pulse magnetron, and particularly lower than the fundamental wave oscillation frequency. An object of the present invention is to provide a pulse magnetron in which spurious generated in a sideband which is a frequency is suppressed.

The pulse magnetron according to the present invention includes an anode formed by providing a plurality of vanes radially on an inner peripheral wall of a cylindrical anode shell, and the anode so as to face the tip portions of the plurality of vanes. A cathode provided along the axial direction at the center of the cathode and a working space in which the surface of the cathode and the tip of the vane face each other are provided so that a magnetic field substantially parallel to the surface of the cathode can be applied. In a pulse magnetron having a pair of pole pieces and operating by a pulse, a groove along the axial direction is formed on the surface of the cathode so as to match a portion facing the tip of each vane of the plurality of vanes. In addition, the thermal electron emission material is applied in the groove to suppress the occurrence of spurious .

  Here, the vane means a part that forms a cavity together with the anode shell, and in addition to a plate-like blade piece fixed to the inner peripheral wall of the anode shell by brazing or the like, like a slot type or a rising sun type, The term includes a portion protruding from the inner periphery of the anode in the case where a cavity is formed by providing a slot or the like in the integral anode.

By chamfering the corners at both ends in the axial direction at the tip of the vane, it is possible to suppress the influence of the electric field nonuniformity in the portion where the magnetic field is stronger, and to reduce the spurious. Can be controlled. The chamfering means processing including R processing for cutting a corner portion into a curved shape, C processing for cutting into a straight shape, and the like.

  With this structure, a thermionic emission material is arranged on the surface of the cathode 2 facing the tip of each vane 12 having the strongest electric field, and when a pulse voltage is applied, a large amount of thermionic emission material on the surface of the cathode 2 is applied. Electron emission occurs and the rated oscillation is reached in a short time. Therefore, as in the conventional case, at a current value lower than the rated current value on a part of the surface of the cathode 2, oscillation other than the rated operating point of oscillation at a frequency lower than the fundamental wave does not occur, and spurious generation is suppressed. Can do.

  Further, by chamfering the both ends of the tip of the vane 12 having a high magnetic flux density so as to increase the distance between the tip of each vane and the surface of the cathode 2 facing the vane 12, a portion with a high electric field is eliminated, and a uniform electric field Similarly, the occurrence of spurious can be suppressed.

  Next, the pulse magnetron of the present invention will be described with reference to the drawings. The pulse magnetron according to the present invention has a structure as shown in FIG. 1 and FIG. 2 showing explanatory views of a longitudinal section and a transverse section of the embodiment. That is, the anode 1 is formed by providing a plurality of vanes 12 radially on the inner peripheral wall of the cylindrical anode shell 11. A cathode 2 is provided at the center of the anode 1, and an anode shell 11 is provided so that a magnetic field substantially parallel to the surface of the cathode 2 can be applied to the working space 4 where the tip of the vane 12 and the surface of the cathode 2 face each other. A pair of pole pieces 3 are provided at both ends in the axial direction. In the present invention, a groove along the axial direction is formed on the surface of the cathode 2, and the groove is formed in accordance with a portion facing the tip of the vane 12 constituting the anode arranged around the cathode, A feature is that a thermionic emission material 22 is coated in the groove.

  As shown in FIGS. 1 and 2, the anode 1 has one end portion of a plurality of vanes (anode pieces) 12 made of a plate material such as oxygen-free copper on the inner peripheral wall of an anode shell 11 made of oxygen-free copper or the like. The other end is fixed toward the center of the anode shell 11, and a cavity 13 that resonates at a desired frequency to be oscillated is formed between the vanes 12. Then, every other vane 12 is connected by a strap 14 so that the π radians phase is different from each other, thereby forming a structure that facilitates π mode oscillation. The anode 1 may not have a structure in which the vane 12 is fixed to the anode shell 11 but may have a structure in which a cavity is formed by forming a slot or the like in an integral anode.

  A cathode 2 is inserted concentrically at the center of the anode shell 11 surrounded by the tip of the vane 12, and a working space 4 is formed between the tip of the vane 12 and the surface of the cathode 2. It is a space where the emitted electrons move. A pair of pole pieces 3 made of a ferromagnetic material such as iron is formed from both axial ends of the anode shell 11 so that a magnetic field substantially parallel to the surface of the cathode 2 can be applied to the working space 4. It is inserted and fixed to the anode shell 11 so that a magnetic field can be applied to the working space 4 by a permanent magnet or an electromagnet (not shown), and is applied to the working space 4 together with the anode voltage applied between the anode and the cathode. Due to the action of the orthogonal electromagnetic field, electrons from the cathode 2 rotate around the cathode 2 to oscillate when energy is given to the cavity 13. A magnetron used in a radar apparatus is pulsed by applying an anode voltage in pulses.

  As shown in FIGS. 1 and 2, the cathode 2 is formed with a groove (concave groove) along the axial direction on the surface of a cylindrical base metal (base metal) 21 based on, for example, nickel. The thermionic emission material 22 is embedded in the groove. As is apparent from FIG. 2, the groove is formed in accordance with a portion facing the tip of each vane 12. Therefore, on the surface of the cathode 2 in the portion facing each tip of the vane 12, the thermoelectron emitting material 22 exists in a portion facing almost the entire area of the tip of the vane 12, and on the side thereof It is characterized by the presence of the base metal 21. The thermionic emission material 22 is the same as the conventional one, but most commonly, a carbonate such as barium, strontium and calcium is filled in the groove and thermally decomposed under vacuum to form an oxide. Oxide is formed. The depth and width of the groove are set so as to match the required amount of thermionic emission material and to allow current to flow through the electron emission material 22 with an appropriate resistance value when an electric field is applied.

  Next, the reason why spurious can be suppressed by forming the cathode 2 in such a structure will be described. When a pulsed anode voltage is applied and the voltage gradually rises, the distance between the anode 1 and the cathode 2 is closest to the tip of the vane 12 and the surface of the cathode 2 at the portion facing the vane 12. Therefore, electrons are emitted all at once from the entire surface of the cathode 2 facing the tip of the vane 12 having the strongest electric field, and oscillation is started at once. That is, the voltage between the anode and the anode of the electron emission portion is constant, and this causes oscillation at a minute level at a frequency lower than the fundamental oscillation frequency that has been generated due to non-uniform electron emission at the time of rising. It is suppressed.

  This is because, when the electron emission material 22 on the entire surface of the conventional cathode 2 is applied, a part of the electron emission material on the entire surface of the cathode 2 facing the tip of the vane 12 having a strong electric field is more than the rated current value. Even when oscillation starts at a low current value or a groove is formed along the axial direction and the electron-emitting material is embedded in the groove, the position is randomly provided regardless of the position of the vane. This is very different from the case where oscillation starts at a current value lower than the rated current value from a part of the electron emitting material on the surface of the cathode 2 facing the tip of the vane 12. In other words, as in the present invention, the electron emitting substance (oxide) coating surface on the cathode 2 and the tip of the vane 12 of the anode 1 are opposed to each other, and if the base metal 22 is other than the opposed portion of the vane 12. Since the electric field of the electron emission surface is uniform and the velocity of the emitted electrons is stabilized, it is easy to gather and form a spoke. As a result, when a certain voltage value is reached at the rise of the anode voltage pulse, oscillation starts stably at one time, and unnecessary oscillation with a low frequency is suppressed.

  FIG. 5 shows the result of examining the oscillation characteristics of the pulse magnetron in the configuration shown in FIG. As is clear from comparison with FIG. 7 showing the spectrum of the conventional structure, according to the present invention, the lobe Q on the lower frequency side as seen from the main lobe has no protrusion, and spurious at a lower frequency is suppressed. It clearly appears that As is apparent from FIG. 5, it can be seen that the protruding portion of the lobe P in the side band on the higher frequency side is also suppressed. This is because the oscillation at the rated value is performed in a short time, and there is no oscillation in other modes.

3 to 4 are enlarged views showing the front end portion of the vane 12 and the facing portion of the cathode 2 which are examples suitable for removing spurious. In other words, the corner 12a of the vane 12 at both ends in the axial direction of the portion facing the cathode at the tip of the vane 12 is chamfered. 3 is chamfered with an arc-shaped R, and the size of R is preferably set to h / 10 or less, where h is the height of the vane 12. This is because the influence of the electric field can be sufficiently avoided if it is equal to or less than h / 10, considering the height of the vane 12 and the change in magnetic flux density in the working space 4 in the height direction of the vane 12. The electric field tends to be high at the corner 12a of the vane, but by using such a shape, there is no particularly high point of the electric field in the working space 4,
When the pulse anode voltage rises, inadvertent emission does not occur, the voltage between the anode 1 and the anode 1 of the electron emission portion becomes constant, and when the pulse application voltage reaches a specific voltage, the emission of electrons does not occur. It happens all at once, and oscillation starts at once. As a result, the spurious suppression effect of the magnetron having the structure shown in FIGS. 1 and 2 can be further improved.

  The structure shown in FIG. 4 is obtained by chamfering the corner 12a of the vane 12 to a straight C surface instead of the R surface of FIG. Even in such a structure, the same effect as the structure shown in FIG. 3 can be obtained by removing the corner 12a of the vane. Also in this case, it is desirable that the length c to be cut is h / 10 or less.

  The present invention can be used as a transmission tube of a radar for fishing boats, aircraft, weather, and the like.

It is explanatory drawing of the longitudinal cross-section which shows one Embodiment of the magnetron by this invention. It is explanatory drawing of the cross section of the magnetron shown in FIG. It is a partial expanded explanatory view which shows the opposing part of the vane which shows other embodiment of the magnetron by this invention, and a cathode. It is a figure similar to FIG. 3 which shows the modification of FIG. It is a figure which shows the oscillation spectrum of the magnetron of the structure shown by FIG. It is longitudinal cross-sectional explanatory drawing which shows an example of the conventional magnetron. It is a figure which shows the oscillation spectrum of the magnetron of the structure shown by FIG. It is explanatory drawing which shows the structure of the cathode of the other example of the conventional magnetron.

Explanation of symbols

1 Anode 2 Cathode 3 Pole piece 4 Working space
11 Anode shell
12 Vane
13 Cavity
14 Strap
21 Base metal
22 Electron emitting materials

Claims (1)

An anode formed by providing a plurality of vanes radially on the inner peripheral wall of the cylindrical anode shell, and an axial direction at the center of the anode so as to face the tip of the plurality of vanes And a pair of pole pieces provided in a working space in which the surface of the cathode and the tip of the vane face each other so that a magnetic field substantially parallel to the surface of the cathode can be applied. In a pulse magnetron that operates with pulses,
In the cathode surface, said plurality of grooves along the axial direction in accordance with the tip facing portion of each vane of the vane is formed by the thermal electron emission material is rubbed into the groove A pulse magnetron characterized by suppressing spurious generation .

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