JPH0817075B2 - Cathode structure for magnetron - Google Patents

Description

TECHNICAL FIELD The present invention relates to a cathode assembly of a magnetron used for microwave heating equipment such as a microwave oven.

2. Description of the Related Art Generally, a magnetron used in a microwave heating device such as a microwave oven has a cathode structure as shown in FIG. This cathode assembly comprises a spiral cathode body 1 made of thorium tungsten, a pair of metal end hats 2 and 3 provided at both ends thereof, and a pair of lead wires 4 extending from the respective end hats 2 and 3. , 5, a stem insulator 6 for hermetically projecting the outer end edges of the lead wires 4, 5 to the outside of the pipe, and an eyelet-shaped metal pipe body 7 in which one opening end face is brazed to the stem insulator 6. Prepare The flange portion 7a on the other open end surface of the metal tube body 7 is airtightly sealed to the anode cylinder body 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 the pair of cathode terminals 10 provided on the outer end surface of the stem insulator 6, and the other end of each choke coil 11 has a high withstand voltage through-type capacitor 12. Is connected to the center electrode 13 of. Then, the metal shield case 14 having the capacitor 12 fixed to the side wall is used as the stem insulator 6 and the choke coil.
Covering 11. Reference numeral 15 indicates a yoke that constitutes an external magnetic circuit.

In the magnetron configured as described above, the LC filter circuit and the shield case 14 configured by the choke coil 11 and the capacitor 12 prevent the microwave component 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.

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention However, since leaked microwaves include not only the fundamental wave component of the oscillating microwave but also harmonic components of several orders, these leaks outside the device can be reliably and efficiently prevented. Is extremely difficult. Also, since the LC filter circuit is held at the cathode potential and the shield case is held at the anode potential (ground), a relatively large shield case is required to prevent sparks from occurring between them, and these reduce the size of the device. In addition, it was a factor to prevent cost reduction.

Means for Solving the Problems In the present invention, a cup-shaped stem insulator is used, and a metal pipe body that surrounds a pair of lead wires extending from each of a pair of end hats and extending toward the stem insulator is provided. , Having a small-diameter tubular extension that fits into the stem insulator. However, this cylindrical extension has a bottom plate portion protruding toward the pair of lead wires, and is approximately 1 / N of the wavelength of the fundamental wave component or arbitrary harmonic component of the oscillating microwave (where N is an arbitrary natural number). ) Has an electrical length corresponding to

Function With this structure, the small-diameter tubular extension that has entered the stem insulator resonates with the specific wavelength component of the microwave leaking to the stem insulator side through the lead wire, and attenuates the component. Since it works, the leaked microwaves can be more attenuated. Also, LC
It is possible to simplify the filter circuit and downsize the circuit components and the shield case. Further, by arranging the high dielectric constant material in the tubular extension, the conventional expensive feedthrough capacitor can be eliminated or downsized.

EXAMPLES Next, the present invention will be described with reference to the examples shown in the drawings.

The structure shown in FIG. 1 is basically different from the structure of the conventional cathode structure shown in FIG.
A cup-shaped ceramic stem insulator 15 is used for hermetically projecting the outer ends of the pair of lead wires 4 and 5 extending from 2, 3 to the outside of the tube, and the anode cylinder. A cylindrical extension 16b having a small diameter in a metal tube body 16 surrounding a pair of lead wires 4 and 5 having a flange portion 16a to be sealed at
And that the tubular extension 16b is inserted into the stem insulator 15 and airtightly sealed, and the tubular extension 16b
Is provided with an annular bottom plate portion 16c protruding toward the pair of lead wires 4 and 5, and the wavelength of the fundamental wave component of the oscillating microwave or the arbitrary harmonic components of the second, third, fourth, etc. is omitted. That is, it has an electric length h corresponding to a quarter.

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

In the embodiment shown in FIG. 2, the bottom plate portion 1 of the tubular extension 16b is
Two through holes 16d and 16e are provided in 6c, and a pair of lead wires 4 and 5 are inserted through these holes.

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

Therefore, the high dielectric constant material 17 and the metallized layer attached thereto serve as a high withstand voltage capacitor, and act as a low-pass filter for leaked microwaves, especially harmonic components. Also, the seismic support strength for the pair of lead wires 4 and 5 is increased.

Cylindrical extension 16b in the embodiment shown in FIGS. 3 and 4.
Is set to approximately 1 / N of the wavelength of the fundamental wave component or arbitrary harmonic component of the oscillating microwave (where 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, the leaked microwaves can be efficiently attenuated before reaching the shield case, the LC filter circuit can be simplified, and the circuit components and the shield case can be downsized. Become. Further, by disposing the high dielectric constant material in the tubular extension, the conventional expensive feedthrough capacitor can be eliminated or downsized.

[Brief description of drawings]

1 to 4 are side sectional views of a cathode assembly for a magnetron embodying the present invention, and FIG. 5 is a side sectional view of a conventional cathode assembly for a magnetron. 1 ... Cathode body, 2, 3 ... End hat, 4,5 ... Lead wire, 15 ... Stem insulator, 16 ... Metal tube, 16b ... Cylindrical extension, 16c ... Bottom plate part, 17 ... High dielectric constant.

Claims (1)

[Claims] 1. A pair of lead wires extending from each of a pair of end hats provided at both ends of a spiral cathode main body and extending toward a cup-shaped stem insulator side are surrounded, and a flange portion is provided with an anode cylinder body. The metal tube body to be sealed is provided with a tubular extension portion having a small diameter that enters into the stem insulator, and the tubular extension portion has a bottom plate portion protruding toward the pair of lead wires, A cathode assembly for a magnetron, which has an electric length corresponding to about 1 / N of a wavelength of a fundamental wave component or an arbitrary harmonic component (where N is an arbitrary natural number).