JP2000299070A - Magnetron - Google Patents

Abstract

PROBLEM TO BE SOLVED: To invariably reduce a spurious level by setting the diameter of the tip face of a pair of pole pieces smaller than the inscribed circle diameter of the inner end faces of anode vanes, and setting the angle between the vertical direction of the tube axis of an anode cylinder and the outer peripheral face of the taper shape of a pair of pole pieces to a specific angle or above. SOLUTION: A cathode 2 is arranged at the center of the tube axis of a cylindrical anode cylinder 1, anode vanes 4 are radially arranged at uniform intervals in an acting space 3 around the cathode 2, and a pair of pole pieces 6 are arranged face to face across the cathode 2 and the acting space 3. The diameter ϕp of the tip faces of the pole pieces 6 is made smaller than the inscribed circle diameter ϕa of the inner end faces of the anode vanes 4. The angle θof a taper formed by a virtual line extended with the tip face of each pole piece 6 in the direction of the anode cylinder 1 and the outer periphery of the pole piece 6 is set to 20 deg. or above, thereby the magnetic flux density at both end sections of the cathode 2 is made 1.1 times the magnetic flux density at the center section of the cathode 2 or above, and a spurious level is improved.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetron for a radar, and more particularly to a structure of an oscillating portion for obtaining a small spurious.

[0002]

2. Description of the Related Art FIG. 8 is a sectional view of a magnetron for a radar designed according to the prior art. A cylindrical cathode 2 is arranged at the center of the tube axis of a cylindrical anode cylinder 1,
Anode vanes 4 are radially arranged around the cathode 2 with a working space 3 therebetween. On the other hand, the magnetic circuit transmits the magnetic force generated by the magnet 5 to the pole piece 6 and opposes the pole piece 6 to form a uniform magnetic field parallel to the working space 3 between the cathode 2 and the anode vane 4. . Note that cathode support rods and the like that are not directly related to the present invention are omitted in the drawings.

[0003] Focusing on the outer shape of the pole piece 6, the magnetic force is transmitted efficiently by narrowing the diameter of the front end surface on the cathode 2 side smaller than the contact surface with the magnet 5. Further, the tip surface of the pole piece 6 on the cathode 2 side is finished to a plane perpendicular to the tube axis of the anode cylinder 1 in order to obtain a uniform magnetic field in a region sandwiching the action space 3 of electrons. Surface diameter (φ
p) is designed to be larger than the inscribed circle diameter (φa) formed by the inner end faces of the anode vanes 4 radially surrounded and arranged at equal intervals.

There is also a design in which a hole is formed in the center of the pole piece 6 so that the input shaft can pass therethrough.
67383) and C-chamfering (45 ° chamfering) may be applied to an edge portion forming a hole. As described above, conventionally, the shape of the pole piece 6 is determined so as to make the magnetic field in the working space 3 of the magnetron uniform. The reason is,
If the magnetic field is not uniform, it has been considered that the magnetic force acting on the electrons becomes non-uniform, the electron orbit is not stabilized, the oscillation spectrum is deteriorated, and the characteristics required for the magnetron cannot be secured. In general, it is a technical common sense that the uniformity of the magnetic field is within 5%. (“MICROWAVE MAGNETRONS” GEORGE B. COLLINS
Edit Refer to Massachusetts Institute of Technology Radiation Research Institute Series 1948. )

[0005]

FIG. 9 shows an output spectrum waveform of a conventional magnetron having an oscillation frequency of 9.4 GHz. In addition to the main oscillation (9.4 GHz) spectrum, there is a spurious around 9.8 GHz. In the magnetron of this example, the spurious level is -29.59 dBc with respect to the main waveform.

In the Radio Law, the spurious level radiated from the radar device is strictly regulated, and the spurious output is required to be -40 dBc or less with respect to the main oscillation output, and the magnetron which generates such spurious is required. When used in a radar device, it is necessary to put a filter in the transmission circuit or in the antenna. For this reason, the structure was complicated and the cost was high. In addition, the majority of current magnetrons are multi-cavity vane strap types because of their relatively stable operation. However, since spurious in this type of magnetron is generated in a frequency band close to the main frequency band, it is difficult to attach a filter or the like to the outside and separate it, which has been a serious problem.

In recent years, the regulation of the spurious emission level from the radar device is becoming stricter. In the conventional magnetron as described above, spurious can be always kept within the regulation value, although other characteristics are sufficiently satisfied. It was difficult and it was very difficult to suppress spurs with higher margins. In light of this situation,
An object of the present invention is to solve the above problems and to provide a magnetron having a low spurious level without using a component such as a spurious reduction filter.

[0008]

A cathode disposed at the center of the tube axis of a cylindrical anode cylinder, and fixed at the inner peripheral surface of the anode cylinder at an equal spacing radially with a working space around the cathode. A pair of pole pieces each having an anode vane arranged and arranged at both ends of the anode cylinder and opposed to each other with the cathode and the working space interposed therebetween and having respective end faces perpendicular to the tube axis of the anode cylinder. Wherein the diameter of each of the tip surfaces of the pair of pole pieces is smaller than the diameter of an inscribed circle formed by the inner end surface of the anode vane, and the respective tip surfaces are perpendicular to the tube axis of the anode cylinder. And forming an imaginary line extending in the direction of the anode cylinder and an outer peripheral surface having a tapered shape such that the diameter of the pair of pole pieces becomes smaller in the direction of the respective end surfaces. By the time more than 20 °,
A magnetron characterized in that the magnetic flux density at both ends of the cathode in the tube axis direction of the anode cylinder in the working space is 1.1 times or more the magnetic flux density at the center of the cathode.

[0009]

With this configuration, the spurious level can be constantly reduced.

[0010]

1 shows a cross section of a magnetron according to an embodiment of the present invention. A cathode 2 is arranged at the center of the tube axis of a cylindrical anode cylinder 1, and anode vanes 4 are radially arranged around the cathode 2 with a working space 3. Further, a pair of pole pieces 6 are opposed to each other with the cathode 2 and the working space 3 interposed therebetween. In the magnetron of this example, unlike the conventional magnetron, the diameter (φp) of each of the opposed end faces of the pole piece 6 is smaller than the inscribed circle diameter (φa) formed by the inner end face of the anode vane 4 (for example, , Φp = 4.2 mm, φa
= 6.9 mm). Also, the angle θ (hereinafter, pole piece tip angle) of a taper formed between an imaginary line obtained by extending each of the opposed tip faces of the pole piece 6 toward the anode cylinder 1 and the outer peripheral face of the pole piece 6 is set to 30 °. I have.

FIG. 2 shows an output spectrum waveform of the magnetron of this embodiment. This spurious level is -62.50 dBc with respect to the main waveform, and the required value is -40.
It clears below dBc.

FIG. 3 shows the magnetic flux density distribution of the magnetic field formed by the pole piece of the magnetron of this embodiment. As shown in the figure, the magnetic flux density in the vicinity of the pole piece tip surface (distance from the pole piece tip surface L = 0.5 mm) is extremely strong. In addition, a portion where the magnetic flux density is large (L = 1 mm) and a portion where the magnetic flux density is small (L = 3 mm) are formed in the working space,
The ratio (magnetic flux density at both ends of the cathode / magnetic flux density at the center of the cathode) was about 1.2.

Conventionally, it has been considered that the magnetic flux density in the working space of the magnetron should be as uniform as possible. However, when various kinds of magnetrons were manufactured and the relationship with the spurious level was investigated, the tube shaft in the working space was found. This time, a new result was obtained that the spurious level was better when the magnetic flux density at both ends of the cathode in the direction was much larger than the magnetic flux density at the center of the cathode.

FIG. 4 shows the results obtained by changing the angle of the tip of the pole piece with the magnetron of this embodiment in order to impart a distribution to the magnetic flux density in the working space. FIG.
The horizontal axis indicates the pole piece tip angle, and the vertical axis indicates the spurious level of the magnetron. At this time, the overall magnetic force was adjusted so that the magnetron current and the magnetron voltage were the same. As can be seen from FIG. 4, the spurious level becomes smaller as the tip angle of the pole piece becomes larger, and good characteristics are obtained. In particular, when the tip angle is 20 ° or more, the required value is -40 dBc or less.

FIG. 5 is a plot of the ratio of the magnetic flux density at both ends of the cathode to the center of the cathode in the working space with respect to the angle at the tip of the pole piece. By making the angle of the tip end of the pole piece acute, the magnetic flux density distribution in the working space becomes non-uniform, and both ends of the cathode, that is, portions near the pole piece are large, and the center of the cathode is small.

4 and 5, if the ratio of the magnetic flux density between both ends of the cathode and the center of the cathode is made 1.1 times or more by setting the tip angle of the pole piece to 20 ° or more, the spurious level becomes -40 dBc. It can be seen that the following can be suppressed.

As described above, the spurious level is improved by giving the magnetic flux density a distribution. The details of the mechanism are unknown at present, but are considered to be as follows. Both ends of the cathode are portions where the shapes of the cathode and the anode are changed, and the electric field is disturbed. The magnetic field may be acting to reduce the electron distribution near the disturbed electric field. By increasing the magnetic field, the electrons are repelled by the mirror effect (a phenomenon in which the lines of magnetic force are repulsed in a region called a mirror where the magnetic field lines converge in a funnel shape) toward the weaker magnetic field, and the electron distribution is shifted to the center of the cathode. Therefore, the ratio of electrons moving uniformly increases and spurious is reduced. What is needed for a magnetron is not a uniform magnetic field, but electrons that move uniformly, and it is thought that the magnetic field needs to have a distribution. At this time, it is naturally necessary to adjust the magnetic force as a whole so that the characteristics of the magnetron current and voltage can be obtained. As the magnetic force at both ends of the cathode is increased, that is, as the ratio of the magnetic flux density is increased, the effect of reducing the spurious effect appears.

FIG. 6 shows another embodiment of the pole piece according to the present invention. The difference from the one shown in FIG. 1 is that in order to obtain the acute angle of the tip of the pole piece 6 which is a feature of the present invention,
The point is that the tapered shape is made into two stages and the acute angle portion is projected. FIG. 7 shows another embodiment of the pole piece according to the present invention. The difference from the one shown in FIG. 1 is that the tip end angle of the pole piece 6 is 90 °. Even in the above-described shape, the above-described effect can be obtained by setting φp smaller than φa and setting the tip angle of the pole piece to 20 ° or more.

[0019]

As described above, according to the present invention, the spurious emission level of the magnetron alone can be stably suppressed at a low level, so that the spurious level of the entire radar apparatus can be further reduced than before. It can be kept low. Further, it is possible to reduce the number of filters conventionally used to reduce spurious, and the effect of contributing to economic efficiency and downsizing is great.

[Brief description of the drawings]

FIG. 1 is a sectional view of a magnetron according to the present invention.

FIG. 2 is an output spectrum waveform of a magnetron according to the present invention.

FIG. 3 is a magnetic flux density distribution of a magnetic field formed by a pole piece according to the present invention.

FIG. 4 shows the relationship between the pole piece tip angle and the spurious level according to the present invention.

FIG. 5 is a diagram showing a ratio between a pole piece tip angle and a magnetic flux density according to the present invention.

FIG. 6 is a cross-sectional view of a magnetron showing another embodiment according to the present invention.

FIG. 7 is a sectional view of a magnetron showing another embodiment according to the present invention.

FIG. 8 is a cross-sectional view of a conventionally designed magnetron.

FIG. 9 is an output spectrum waveform of a magnetron according to a conventional design.

[Explanation of symbols]

 1. Anode cylinder 2. Cathode 3. Working space Anode vane 5. Magnet 6. Pole piece

Claims (1)

[Claims] 1. A cathode disposed at the center of a tube axis of a cylindrical anode cylinder, and a cathode fixed to an inner peripheral surface of the anode cylinder and arranged radially at equal intervals around an operating space around the cathode. A magnetron comprising a pair of pole vanes having an anode vane and a pair of pole pieces provided at both ends of the anode cylinder and disposed opposite to each other with the cathode and the working space interposed therebetween and having respective tip surfaces perpendicular to the tube axis of the anode cylinder. The diameter of each of the tip surfaces of the pair of pole pieces is smaller than the diameter of an inscribed circle formed by the inner end surface of the anode vane, and the respective tip surfaces are perpendicular to the tube axis of the anode cylinder. The angle formed between the imaginary line extending in the direction and the outer peripheral surface having a tapered shape whose diameter decreases in the direction of the respective tip end surfaces of the pair of pole pieces is 20 ° or more Wherein the magnetic flux density at both ends of the cathode in the tube axis direction of the anode cylinder in the working space is 1.1 times or more the magnetic flux density at the center of the cathode.