JPH0817076B2 - 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 airtightly projecting the outer end portions of the lead wires 4, 5 to the outside of the tube, and an eyelet-shaped metal tube body 7 in which one opening end surface is brazed to the stem insulator 6. Prepare However, the flange portion 7a on the other open end surface of the metal tube body 7 is hermetically sealed to the anode cylinder body 9 in a relation 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 penetrates the respective high withstand voltage. It is connected to the center electrode 13 of the mold capacitor 12. A metal shield case 14 having a capacitor 12 fixed to the side wall accommodates the stem insulator 6 and the choke coil 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.

However, since the leaked microwave includes not only the fundamental wave component of the oscillating microwave but also the second, third, fourth, etc. harmonic components, these leak out of the device. It is extremely difficult to prevent this reliably and efficiently. Also, the feedthrough capacitor is expensive, and 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 is used to prevent sparks from occurring between the two. A case is required, which has been a factor that hinders downsizing of the device and cost reduction.

Means for Solving the Problems In the present invention, while using a cup-shaped stem insulator, while surrounding a pair of lead wires extending from each of a pair of end hats toward the stem insulator side, and a flange portion In (1), the metal tubular body sealed to the anode tubular body is provided with a tubular extension portion having a small diameter which is inserted into the stem insulator. The tubular extension portion has a bottom plate portion having a hole through which the pair of lead wires are inserted, and houses a resonant element that is at least high-frequency coupled to the lead wires. However, the resonant element has a ring-shaped high dielectric constant body through which the lead wire is inserted, and a pair of conductive films attached to both end surfaces of the high dielectric constant body, and one of the conductive films is It is connected to the bottom plate part.

Action With this configuration, since the tubular extension having the small diameter enters the stem insulator to perform a shield action, not only can microwaves that pass through the stem insulator and leak to the outside of the tube be reduced, Since the resonant element housed in this part resonates with the specific wavelength component of the leaking microwave and effectively blocks extravasation of the same component as a resonant filter exhibiting high impedance characteristics at the specific wavelength, conventional LC It is possible to simplify or downsize the filter circuit and the shield case.

EXAMPLE The structure of the present invention shown in FIG. 1 is basically different from the structure of the conventional cathode structure shown in FIG. 4 in that a pair of lead wires 4 extending from a pair of end hats 2 and 3 is used. A ceramic stem insulator 16 for hermetically projecting the outer ends of the first and the second outer casings 5 is formed into a cup shape, and a flange portion 17a to be sealed to the anode cylinder has a large diameter opening. A metal tube body 17 having an end and surrounding the pair of lead wires 4 and 5 has a tubular extension portion 17b having a small diameter, and the tubular extension portion 17b is the stem insulator 16
In addition, the bottom plate portion 17c provided in the cylindrical extension 17b has a hole for inserting the lead wires 4 and 5, and each lead wire 4 ,Five
Two resonant elements 18 surrounding and surrounding at high frequency
Is provided on the bottom plate portion 17c. However, the resonance element 18 is composed of a lead-shaped high dielectric constant material 18a and a pair of conductive films 18b and 18c attached to both end surfaces thereof, and the conductive film 18c on the lower surface side is brazed to the bottom plate portion 17c. .
The high-dielectric constant body 18a is made of a ceramic having a dielectric constant ε of 30 to 90, and the pair of conductive films 18b, 18c is a two-layer structure in which a plating layer is stacked on the metallized layer. Further, the depth h of the cylindrical extension 17b is set to an electrical length that substantially matches a natural fraction of the wavelength of the arbitrary harmonic component of the oscillating microwave.

The conductive film 18b on the upper surface side of both resonant elements 18 is not in contact with the lead wire penetrating the resonant element, but the lead wire 4,
The specific wavelength component of the microwave leaked to the stem insulator 16 side through 5 resonates in the resonance element 18. That is, since the resonance element 18 is a ring resonator having high impedance characteristics in a specific frequency band, leakage of the microwave component out of the tube is prevented. Further, since the cylindrical extension portion 17b has a shielding function, the microwave transmitting region of the stem insulator 16 can be reduced. Further, the choke effect of the tubular extension 17b can also attenuate the specific harmonic component of the leaked microwave.

In the embodiment shown in FIG. 2, the conductive films on the upper surfaces of the two resonant elements 18 are directly connected to the lead wires by eyelet-shaped metal pieces 18c. In this case, each resonant element 18 also functions as a capacitor due to the high dielectric constant material, and
Since it is ideally connected in parallel to a conventional feedthrough capacitor, there is an advantage that the feedthrough capacitor can be eliminated or miniaturized in addition to the effect described in the above-mentioned embodiment.

In the embodiment shown in FIG. 3, the high dielectric constant material 18 of the resonant element 18 is used.
By providing a protrusion on the lower surface of a and fitting the protrusion into the hole of the bottom plate portion 17c, the position regulating effect of the resonance element 18 is obtained.

As described above, according to the present invention, microwave leakage can be efficiently prevented in the magnetron tube, and the tubular insulator of the metal tube body held at the anode potential (ground) prevents the leakage of microwaves. Can be shielded, and the LC filter circuit can be simplified and the circuit components and shield case can be downsized.

[Brief description of drawings]

1 to 3 are side sectional views of a cathode assembly for a magnetron embodying the present invention, and FIG. 4 is a sectional side view of a conventional cathode assembly for a magnetron. 1 ... Cathode body, 2, 3 ... End hat, 4,5 ... Lead wire, 16 ... Stem insulator, 17 ... Metal tube, 17b ... Cylindrical extension, 17c ... Bottom plate part, 18 ... Resonant element.

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 an anode cylinder is formed. A metal tube body having a flange portion to be sealed is provided with a tubular extension portion having a small diameter that is inserted into the stem insulator, and the tubular extension portion is a bottom plate having a hole through which the pair of lead wires are inserted. A resonance element that has a portion and that is coupled to the lead wire at least at high frequencies is housed, and the resonance element has a ring-shaped high dielectric constant body through which the lead wire is inserted, and both end surfaces of the high dielectric constant body. And a pair of conductive films attached to the base plate, one of the conductive films being connected to the bottom plate portion.