JP3087351B2 - Magnetron - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a continuous wave magnetron in the 2.45 GHz band widely used in microwave ovens and the like, which is generated, for example, in a short time immediately after power-on (.pi .-. Pi.).
1) The present invention relates to a magnetron configured to prevent a radio wave caused by abnormal oscillation in a mode from being radiated to the outside and interfering with a device using a weak radio wave.

[0002]

2. Description of the Related Art IS used for microwave ovens, etc.
Magnetrons in the M band (industrial, scientific, and medical bands) are designed to have a normal oscillation, that is, an oscillation frequency in the π mode of 2.45 GHz.

FIG. 3 is a sectional view taken along a plane including a tube axis, showing a typical structure of a magnetron for a microwave oven.
Is an anode, 2 is an anode cylinder, 3 is a vane radially arranged from the inner circumference of the anode cylinder toward the tube axis, 3b and 3c are strap grooves, 4, 6 are outer straps, 5, 7 are inner straps,
8 is a cathode, 8a is a filament serving as an electron emission source, 9 is a magnetic pole for forming a static magnetic field in a tube axis direction in a so-called working space around the cathode, 10 is a permanent magnet serving as a magnetomotive force source for forming the magnetic field, Numeral 11 denotes a yoke for forming a return path of the magnetic field magnetic flux, 12 denotes a filter case having a built-in filter for preventing a microwave from leaking to a power supply line for supplying power to the cathode, and 13 denotes one end connected to one of the vanes. A microwave output portion having a built-in end obtained by sealing and cutting off the obtained microwave power extraction line 13a together with a copper exhaust pipe, and a bottomed portion 14 supporting an exhaust pipe penetrating the uncut portion of the exhaust pipe and the bottom center thereof. A second harmonic suppression choke 15 formed by the cylindrical sealing fitting 14a and the microwave power output line 13a is a cooling fin that is in close contact with the outer wall of the anode cylinder.

The normal oscillation mode of the magnetron, that is, the oscillation in the π mode, is well understood theoretically, and a magnetron for a microwave oven or the like is designed to be compatible with the 2.45 GHz ISM band. Since these magnetrons are widely used for microwave ovens, etc., the fundamental wave is regulated worldwide by laws and regulations so that the radiation of unnecessary waves from these magnetrons does not interfere with other radio equipment using noise. It is regulated so that unnecessary harmonics other than those are not radiated. Therefore, the magnetron shown in FIG. 3 is also provided with a choke 14 for suppressing the second harmonic. Various types of chokes for suppressing harmonics have been proposed. In addition to the above-described structure, for example, Japanese Utility Model Laid-Open Publication No. Sho 54-125564 discloses a portion of a microwave output line relatively close to a magnetic pole. There is disclosed a technique of providing a choke made of a metal cylinder having two types of large and small diameters by providing a stepped portion in the middle around the periphery.

[0005]

The effect of the choke on harmonics is great, but the frequency range that can be trapped is relatively narrow, so in some cases, a plurality of chokes may be provided for one harmonic. In addition, the emission of unnecessary waves due to harmonics has been suppressed to below the regulation value by law.

In a normal oscillation mode, a magnetron having a plurality of vanes protruding from the inner periphery of the anode cylinder toward the tube axis has a plurality of cavity resonators formed on the inner periphery of the anode which are adjacent to each other. A π mode oscillation having a phase difference of opposite phase, that is, π, is generated and is designed to be used continuously in this state, but the amount of electron emission from the cathode is insufficient, for example, a short time after power-on. During time, the so-called (π
1) Abnormal oscillation may occur in the mode. When there are N cavity resonators (that is, N vanes), the normal oscillation π mode is the N / 2th mode, and the (N / 2) -1 mode is the so-called (π-1) mode. . Various measures have been taken to suppress the (π-1) mode in operations that intermittently repeat pulse oscillation with high power, such as magnetrons used in pulse radars. However, the (π-1) mode of the abnormal oscillation mode that occurs only for a short time after the power is turned on hardly causes a problem, and the frequency at the time of the abnormal oscillation is considered. I didn't. Conventionally, in the case of a large number of magnetrons manufactured for microwave ovens, the oscillation frequency in the (π-1) mode is 4.7 to 4.8 GHz or 4.15 to 4.2.
It was often 5 GHz.

[0007] With the rapid progress of communication technology in recent years, various services using satellite communication are increasing. For example, 3.26 to 3.267, 3.332 to 3.339,
3.3458 to 3.358, 4.8 to 5.0, GHz are used for radio astronomical observation, and 3.6 to 4.2, 4.5 to
4.8 GHz is allocated for satellite communication. When a radio wave from a satellite is received on the ground, the signal radio wave is weak, so that the radio wave is easily disturbed. In particular, the 3.6 to 4.2 GHz band is a paid TV service in the United States for CATV (originally a pay TV service using a cable laid out door by door, but is economical when targeting a vast area). TV broadcasting waves are broadcasted from satellites.

[0008] Since microwave ovens using magnetrons are very widely used, if the above-mentioned radio waves due to the abnormal oscillation of the magnetrons are left undisturbed, even if the microwaves are radiated from individual microwave ovens for a short period of time. However, there is a possibility that the device using the weak radio waves will be disturbed. Actually, when a receiving antenna for CATV was installed in an existing house, an apartment was constructed on a straight line connecting the satellite and the antenna, and the apartment was interposed in the part with high directivity of the antenna. There are also reports that the range was used and interfered with CATV reception.

According to the present invention, when used in a microwave oven or the like, a CAT utilizing a weak radio wave from a satellite as described above is used.
An object of the present invention is to provide a magnetron that does not have a risk of interfering with a V broadcast or the like.

[0010]

According to the present invention, in order to achieve the above object, in a normal oscillation mode, that is, in an ISM band magnetron having an oscillation frequency of 2.45 GHz in a π mode, a so-called (π-1) mode is used. The oscillation frequency at the time of abnormal oscillation is set to 4.9 ± 0.1 GHz which is almost the same frequency as the second harmonic at the time of π mode oscillation. On the other hand, as described above, at present, there are legal restrictions on the emission of harmonics when magnetrons for microwave ovens are oscillating normally, and these magnetrons usually suppress the second harmonic. The choke is provided as an additional feature. Therefore, according to the present invention, the so-called (π-
1) If the abnormal oscillation frequency in the mode is set to be the same as the frequency of the second harmonic of the π-mode oscillation, trapping by the existing choke and radiation as unnecessary radio waves are prevented.

[0011]

As described above, the abnormal oscillation frequency of the conventional magnetron for microwave oven in the (π-1) mode is usually 4.7 to 4.7.
It was often 4.8 GHz or 4.15 to 4.25 GHz.

As described above, the normal oscillation of the magnetron, that is, the π-mode oscillation, has been well understood, and a large number of cavities are formed by projecting a large number of vanes from the inner periphery of the anode cylinder toward the tube axis. It has been found that the shape and dimensions of the straps that electrically short-circuit the portions that are to have the same phase in the resonance state of each cavity resonator have an influence on the normal oscillation frequency of the magnetron having the above-mentioned structure. The inventor has set the oscillation frequency in the π mode to 2.45.
While maintaining the frequency in GHz, the shape and dimensions of the strap are determined so that the oscillation frequency in the (π-1) mode matches the frequency of the second harmonic during the π mode oscillation, and systematic trial production experiments are performed to obtain desired characteristics. The shape and dimensions of the strap were found. In fact, it has been confirmed that the magnetron using this strap can also suppress the emission of unnecessary waves due to abnormal oscillation in the (π-1) mode along with the second harmonic.

[0013]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. FIG. 1 is a sectional view including a tube axis of an anode used in one embodiment of the present invention, and FIG. 2 is a bottom view of the anode. In the figure, 1 is an anode (entire), 2 is an anode cylinder, 3 is a vane, 3a is a vane tip, 3b and 3c are strap grooves, 4 and 6 are outer straps, and 5 and 7 are inner straps. As can be seen from FIGS. 1 and 2, these straps 4, 5, 6, and 7 have the inner strap 5 in the upper strap groove 3b in the same vane.
Is connected to the vane, the outer strap 6 is connected to the vane in the lower strap groove 3c.
In the vane adjacent to the above-mentioned vane, the outer strap 4 is connected to the vane in the upper strap groove 3b, and the inner strap 7 is connected to the vane in the lower strap groove 3c. Such a structure is a method conventionally employed to further stabilize the π-mode oscillation.

Here, the diameter of the anode cylinder is A, the diameter at the vane tip 3a is F, the thickness of the vane is W, the height of the vane is G, the inner and outer diameters of the inner strap are E and D, and the inner and outer diameters of the outer strap are respectively. Are C and B, respectively. The inventor investigated the frequency of the (π-1) mode while changing the dimensions of the strap and the dimensions of the strap groove so that the oscillation frequency of the π mode was fixed at 2.45 to 2.465 GHz. One example is described below.

A = 35.1 mm, F = 8.9 mm, G =
9.8 mm, W = 2 mm, B = 16.1 mm, C = 1
When 5.0 mm, D = 13.5 mm, and E = 12.4 mm, the oscillation frequency of the (π-1) mode is 4.9 GHz.
It became. The average strap diameter = 1/4 under the above conditions.
(B + C + D + E) was 14.25 mm.

Under the above conditions, when D = 13.6 mm, the oscillation frequency of the (π-1) mode is 4.94 G
Hz.

In the above magnetron, the frequency of the second harmonic of the π mode oscillation and the frequency of the (π-1) mode oscillation are in the same frequency band. Therefore, the π-mode second harmonic suppression choke additionally installed in the microwave output unit is not only the π-mode second harmonic, but also (π-
1) Mode radio wave radiation can also be suppressed. By setting the average strap diameter to 13.5 to 15.0 mm, the frequency in the (π-1) mode could be matched to the second harmonic frequency 4.9 ± 0.1 GHz in the π mode.

[0018]

As described above, according to the present invention,
Since the frequency of the (π-1) mode is set to coincide with the frequency of the second harmonic of the π mode, the π mode second harmonic emission suppression conventionally provided in the microwave output unit is conventionally provided. With the choke structure, the emission of unnecessary (π-1) mode radio waves can be suppressed, and a low-noise magnetron can be realized without increasing the cost while maintaining the conventional number of components.

[Brief description of the drawings]

FIG. 1 is a sectional view of a plane including a tube axis of an anode used in an embodiment of the present invention.

FIG. 2 is a bottom view of the anode.

FIG. 3 is a cross-sectional view taken along a plane including a tube axis, showing a typical structure of a magnetron for a microwave oven.

[Explanation of symbols]

2 ... Anode cylinder, 3 ... Vane, 3b, 3c ... Strap groove, 4,6 ... Outer strap, 5,7 ... Inner strap.

Claims (2)

(57) [Claims] In an ISM band magnetron having an oscillation frequency of 2.45 GHz in a normal oscillation mode, that is, a π mode, an oscillation frequency at the time of abnormal oscillation in a so-called (π-1) mode is set to a second oscillation frequency in a π mode oscillation. A magnetron, wherein the frequency is set to 4.9 ± 0.1 GHz which is substantially the same as the harmonic. 2. A choke structure for suppressing a second harmonic is added to a microwave output extracting section.
The magnetron described.