JPH056739A - Magnetron - Google Patents

Abstract

(57) [Abstract] [Purpose] To provide a magnetron in which radio waves during (π-1) mode oscillation do not interfere with weak radio wave utilization equipment such as CATV satellite broadcasting. [Structure] Adjusting the shape and average diameter of the strap that electrically short-circuits the sites of the magnetron anode vanes that should be in the same phase during π-mode oscillation, and adjusts the frequency during (π-1) -mode oscillation to the π-mode. The frequency is set to 4.9 ± 0.1 GHz, which is almost the same as the second harmonic during oscillation, and trapped in the existing choke of the magnetron.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention provides a 2.45 GHz band continuous wave magnetron which is widely used in microwave ovens, etc. (π-
1) The present invention relates to a magnetron capable of preventing radio waves due to abnormal oscillation of a mode from being emitted to the outside and interfering with weak radio wave utilizing devices.

[0002]

2. Description of the Related Art IS used for microwave ovens
The M-band (industrial, scientific, medical band) magnetron is designed so that the oscillation frequency in normal oscillation, that is, π mode is 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 and 6 are outer straps, 5 and 7 are inner straps,
Reference numeral 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 the 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, Reference numeral 11 is a yoke forming a return path of the magnetic flux of the acting magnetic field, 12 is a filter case containing a filter for preventing microwaves from leaking to a power supply line for supplying electric power to the cathode, and 13 is one end connected to one of the vanes. A microwave output part having a built-in end portion obtained by sealing the cut microwave power extraction line 13a together with an exhaust pipe made of copper, and 14 having a bottom for supporting the exhaust pipe penetrating the uncut portion and the bottom center of the exhaust pipe. A second harmonic suppressing choke formed by the cylindrical sealing metal member 14a and the microwave power take-out line 13a, and 15 is a cooling fin closely attached to the outer wall of the anode cylinder.

The normal oscillation mode of the magnetron, that is, the oscillation of the π mode has been well understood theoretically, and the magnetron for microwave ovens and the like is designed to be compatible with the 2.45 GHz ISM band. Since these magnetrons are extremely widely used for microwave ovens, etc., in order to prevent unwanted wave radiation from these magnetrons from interfering with other radio wave-using equipment as noise, the fundamental wave is regulated worldwide by laws and regulations. It is regulated so that unnecessary harmonics other than those are not emitted. Therefore, the magnetron shown in FIG. 3 is also provided with the choke 14 for suppressing the second harmonic. Various proposals have been made for chokes for suppressing harmonics. In addition to the above structure, for example, in Japanese Utility Model Laid-Open Publication No. 54-125564, a portion of a microwave output lead wire relatively close to a magnetic pole is disclosed. There is disclosed a technique in which a choke made of a metal cylinder having two kinds of diameters, large and small, is provided by providing a step portion in the middle around the choke.

[0005]

Although the chokes have a great effect on the harmonics, the frequency range in which they can be trapped is relatively narrow. Therefore, in some cases, a plurality of chokes may be arranged for one harmonic. The emission of unnecessary waves due to harmonics has been conventionally suppressed below the regulation value by law.

In the normal oscillation mode, the magnetron in which a plurality of vanes are projected from the inner circumference of the anode cylinder toward the tube axis has a structure in which, in the normal oscillation mode, adjacent cavity resonators of a plurality of cavity resonator groups formed on the inner circumference of the anode are mutually adjacent. Although π-mode vibrations with opposite phases, that is, π different in phase, are generated, and it is designed to be used continuously in this state, but the amount of electron emission from the cathode is insufficient, for example, short after power-on. During time, the so-called (π
Abnormal oscillation may occur in -1) 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 actions are taken to suppress the (π-1) mode in operations such as pulse oscillations that intermittently repeat pulse oscillation with high power, for example, in a magnetron used for pulse radars, but in a magnetron for a microwave oven that is used continuously. , The (π-1) mode of the abnormal oscillation mode that occurs only for a short time after the power is turned on has almost no problem, and the value of the frequency at the abnormal oscillation is also taken into consideration. Didn't. In the case of many magnetrons that have been conventionally 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.

With the recent breakthrough in communication technology, various services using satellite communication are increasing. For example, 3.26 to 3.267, 3.332 to 3.339,
3.3458-3.358, 4.8-5.0, GHz for radio astronomical observation, 3.6-4.2, 4.5-
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, and thus it is easily disturbed. In particular, the 3.6 to 4.2 GHz band is a pay TV service for CATV in the United States (originally, it is a pay TV service that uses a cable wired in a door, but it is economical when targeting a vast area. (Satellite is used due to problems) TV broadcasting waves are being broadcast from the satellite.

Microwave ovens using magnetrons are extremely widely used. Therefore, if the radio waves due to the abnormal oscillation of the magnetrons are left unchecked, even individual microwave ovens transiently radiate for a short time. However, there is a possibility that the device using the weak radio waves may be disturbed. Actually, when the receiving antenna for CATV is installed in the existing house, the apartment was built on the straight line connecting the satellite and the antenna, and the apartment was placed in the part where the antenna has a large directivity. It has also been reported that the range was used and interfered with CATV reception.

The present invention, when used in a microwave oven or the like, uses a weak radio wave from the satellite as described above.
It is an object of the present invention to provide a magnetron that does not have a risk of interfering with V broadcasts.

[0010]

In order to achieve the above object, the present invention provides an ISM band magnetron having an oscillation frequency of 2.45 GHz in a normal oscillation mode, that is, a π mode, in a so-called (π-1) mode. The oscillation frequency during abnormal oscillation is set to 4.9 ± 0.1 GHz, which is almost the same frequency as the second harmonic during π-mode oscillation. On the other hand, as mentioned above, there are currently legal restrictions on the emission of harmonics when the magnetrons for microwave ovens are normally oscillating, and these magnetrons usually suppress the second harmonics. It is equipped with a choke to do it. Therefore, according to the present invention, the so-called (π-
If the abnormal oscillation frequency in the 1) mode is set to be the same as the frequency of the second harmonic of the π-mode oscillation, it is prevented from being trapped by the existing choke and being radiated as unnecessary radio waves.

[0011]

As described above, the abnormal oscillation frequency in the (π-1) mode of the conventional magnetron for a microwave oven is usually 4.7 to.
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 already well understood, and a large number of cavity resonator groups are formed by projecting a large number of vanes from the inner circumference of the anode cylinder toward the tube axis. It has been known that the shape and size of straps that electrically short-circuit and connect the portions of the respective cavity resonators that should be in the same phase in the resonance state have an influence on the normal oscillation frequency of the magnetron. The present inventor has set the oscillation frequency in the π mode to 2.45.
While maintaining at GHz, the shape and dimensions of the strap were calculated so that the oscillation frequency in the (π-1) mode matches the frequency of the second harmonic during π-mode oscillation, and systematic trial experiments were conducted to obtain the desired characteristics. Found the shape and dimensions of the strap. It was confirmed that the magnetron using this strap can suppress not only the second harmonic but also the emission of unnecessary waves due to the abnormal oscillation of the (π-1) mode.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in more detail below with reference to the drawings. 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 (whole), 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 same vane, and in the upper strap groove 3b, the inner strap 5
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 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 that has been conventionally adopted to further stabilize π-mode oscillation.

Here, the diameter of the anode cylinder is A, the diameter at the tip of the vane 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 present inventor investigated the frequency of the (π-1) mode while changing the size of the strap and the size of the strap groove so as to fix the oscillation frequency of the π mode to 2.45 to 2.465 GHz. One example will be 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.
Became. Under the above conditions, the average strap diameter = 1/4
-(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.
Became 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 choke for suppressing the second harmonic of the π mode, which is additionally installed in the microwave output unit, not only the second harmonic of the π mode, but also (π−
1) The emission of radio waves in mode can also be suppressed. By setting the average strap diameter to 13.5-15.0 mm, it was possible to match the frequency of the (π-1) mode with the second harmonic frequency of π mode of 4.9 ± 0.1 GHz.

[0018]

As described above, according to the present invention,
Since the frequency of the (π-1) mode is set to match the frequency of the second harmonic of the π mode, the frequency of the second harmonic emission suppression of the π mode, which is conventionally additionally provided in the microwave output unit, is used. With the choke structure, it is possible to suppress the emission of unnecessary radio waves in the (π-1) mode, and it is possible to realize a low noise magnetron with the same number of conventional components without increasing the cost.

[Brief description of drawings]

FIG. 1 is a sectional view taken along 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 sectional view of 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)

[Claims] 1. An ISM band magnetron having an oscillation frequency of 2.45 GHz in the normal oscillation mode, that is, the oscillation frequency at the time of abnormal oscillation in the so-called (π-1) mode is the second oscillation frequency in the π mode oscillation. A magnetron characterized by being set to 4.9 ± 0.1 GHz, which has almost the same frequency as the harmonics. 2. The microwave output extraction portion is provided with a choke structure for suppressing second harmonics.
The described magnetron.