JPH0224936A - Cathode structure for magnetron - Google Patents

Abstract

PURPOSE:To decrease leakage micro-waves and constructing circuit parts and shield case in small size by extending a metal tubing surrounding leads of an end hat into cup-shaped stem insulation, and specifying the length of this extended part. CONSTITUTION:Stem insulation 15 is made in cup form, and a cylindrical extension part 16b is furnished in a metal tubing 16 surrounding leads 4, 5 and inserted into the insulation 15 followed by sealing air-tightly. This extension part 16b is provided with a ring-shaped bottom plate and given an electrical length h which is corresponding to one integer fraction of the wavelength of any high-harmonic component or fundamental wave component of the oscillated micro-waves.Thereby the specific components of micro- waves leaked through the leads 4, 5 to the insulation 15 side are damped upon making resonance by a chock formed by the extension part 16b and bottom plate 16c. Thus an LC filter circuit can be simplified and the circuit components and shield case be constructed in small size.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a cathode structure of a magnetron used in microwave heating equipment such as a microwave oven.

2. Description of the Related Art Generally, a magnetron used in microwave heating equipment such as a microwave oven has a cathode structure as shown in FIG. This cathode structure includes a spiral cathode body 1 made of thorium tungsten, a pair of metal end hats 2 and 3 provided at both ends, and each end hat 2.3.
A pair of lead wires 4.5 extending from the lead wire 4.
, 5, the stem insulator 6 hermetically protrudes the outer edges of the tube
and an eyelet-shaped metal tube 7 whose one open end surface is brazed to the stem insulator 6. The 7 flange portion 7a on the other open end surface of the metal tube body 7 is hermetically sealed to the anode face piece 9 so as to cover the magnetic pole piece 8 provided thereon.

On the other hand, one end of a choke coil 11 is connected to each of a pair of cathode terminals 10 attached on the outer end surface of the stem insulator 6, and the other end of each choke coil 11 is connected to a feedthrough capacitor 12 with high withstand voltage. is connected to the center electrode 13 of. A metal shield case 14 having a capacitor 12 fixed to its side wall covers the stem insulator 6 and the choke coil 11. Reference numeral 15 indicates a yoke constituting the external magnetic circuit.

In the magnetron configured in this way, L is configured by a choke coil 11 and a capacitor 12.
Since the C filter circuit and the shield case 14 prevent microwave components leaking through the lead wires 4 and 5 from leaking out of the device, it is possible to prevent communication interference due to leaked microwaves.

Problems to be Solved by the Invention However, since the leaked microwave contains not only the fundamental wave component of the oscillated microwave but also several harmonic components,
It is extremely difficult to reliably and efficiently prevent these leaks from outside the device. In addition, since the LC filter circuit is held at cathode potential and the shield case is held at anode potential (ground), a relatively large shield case is required to prevent sparks between the two, which reduces the size of the device. This was a factor that hindered cost reduction.

Means for Solving the Problems In the present invention, a tip-shaped stem insulator is used, and a metal tube surrounding a pair of lead wires extending from each of a pair of end hats and directed toward the stem insulator side includes: The stem has a small diameter cylindrical extension extending into the stem insulator. However, this cylindrical extension has a bottom plate portion that protrudes toward the pair of lead wires, and is approximately one-Nth of the wavelength of the fundamental wave component or arbitrary harmonic component of the oscillated microwave (where N is an arbitrary natural number). ).

With this structure, the small-diameter cylindrical extension that has entered the stem insulator leaks through the lead wire to the stem insulator, resonates with a specific wavelength component of the microwave, and attenuates the same component. Since it acts as a choke, it is possible to attenuate more leakage microwaves.
It is also possible to simplify the filter circuit and downsize the circuit components and shield case. Furthermore, by disposing a high dielectric constant material within the cylindrical extension, conventional expensive feedthrough capacitors can be eliminated or downsized.

Embodiments Next, the present invention will be explained along with embodiments shown in the drawings.

The structure shown in FIG. 1 is basically different from the structure of the conventional cathode structure shown in FIG.
, 3, the outer ends of the pair of lead wires 4.5 extending from the tube are airtightly protruded out of the tube, and the ceramic stem insulator 15 is shaped like a pot. Having a flange portion 16a to be sealed at the large diameter opening end,
The metal tube 16 surrounding the pair of lead wires 4 and 5 has a small-diameter cylindrical extension 16b, and the cylindrical extension 16b is inserted into the stem insulator 15 and hermetically sealed. This cylindrical extension part 16b has an annular bottom plate part 16c extending to the pair of node lines 4 and 5, and also has a fundamental wave component of the oscillated microwave or arbitrary harmonics such as the second, third, fourth, etc. It has an electrical length corresponding to approximately one-fourth of the wavelength of the wave component.

In this case, the specific wavelength component of the microwave leaked to the stem insulator 15 side through the lead wires 4 and 5 resonates and is attenuated by the choke formed by the small-diameter cylindrical extension 6b and the bottom plate portion 16c.

In the embodiment shown in FIG. 2, the bottom plate portion 16c of the cylindrical extension 16b has two through holes 16d and 16e, through which a pair of lead wires 4 and 5 are inserted, one at a time.

In each of the embodiments shown in FIGS. 3 and 4, a ceramic disc-shaped high dielectric constant body 17 is disposed within the cylindrical extension 16b of the metal tube 16. This high dielectric constant material 17 is
The cylindrical extension 16b has a first metallized layer on the side that is in close contact with the bottom plate portion 16c, and a second metallized layer is provided on the inner peripheral surface of at least one of the two through holes through which the pair of lead wires 4 and 5 are inserted. It has a metallized layer. The first metallized layer is brazed to the bottom plate portion 16c, and the second metallized layer is brazed to the lead wire.

Therefore, the high dielectric constant material 17 and the metallized layer attached thereto become a high withstand voltage capacitor, and act as a low-pass filter against the harmonic components of the leaked microwave. Increase the seismic support strength for 5.

Cylindrical extension 16b in the embodiment shown in FIGS. 3 and 4
The electrical length of is set to approximately 1/N of the wavelength of the fundamental wave component or arbitrary harmonic component of the oscillated microwave (N is an arbitrary natural integer), and N is the dielectric constant of the high dielectric constant material 17 used. determined by

Effects of the Invention According to the present invention, as described above, it is possible to efficiently attenuate leaked microwaves before reaching the shielding case, and it is also possible to simplify the LC filter circuit and downsize the circuit components and the shielding case. Become. Furthermore, by disposing a high dielectric constant material within the cylindrical extension, conventional expensive feedthrough capacitors can be eliminated or downsized.

[Brief explanation of the drawing]

1 to 4 are side sectional views of a magnetron cathode assembly embodying the present invention, and FIG. 5 is a side sectional view of a conventional magnetron cathode assembly. 1... Cathode body, 2, 3... End hat, 4゜5... Lead wire, 15...
Stem insulator, 16...Metal tube body, 16b...
...Cylindrical extension part, 16c...Bottom plate part, 1
7...High dielectric constant material. Name of agent: Patent attorney Shigetaka Awano and 1 other person! -Fukumayusereikai, Figure 4, Figure 2

Claims (1)

[Claims] A metal that surrounds a pair of lead wires that extend from a pair of end hats provided at both ends of the spiral cathode body and go toward the cup-shaped stem insulator, and is sealed to the anode cylinder at the flange. The tubular body includes a small-diameter cylindrical extension that enters into the stem insulator, and this cylindrical extension has a bottom plate portion that projects toward the pair of lead wires, and the cylindrical extension has a bottom plate portion that extends toward the pair of lead wires, and a fundamental wave component of the oscillated microwave or an arbitrary cylindrical extension. A cathode structure for a magnetron, characterized in that it has an electrical length corresponding to approximately 1/N of the wavelength of a harmonic component (where N is an arbitrary natural number).