JPH0230035A - Cathode structure for use in magnetron - Google Patents

Abstract

PURPOSE:To efficiently stop leakage of micro waves by providing a resonant element with a ring-shaped high-rate dielectric having a lead wire inserted therein and a pair of conductive coats provided at opposite ends of this high-rate dielectric, and connecting one of these conductive coats to its bottom panel portion. CONSTITUTION:A ceramic stem insulator 16 is formed which is in the form of a cup and adapted to force respective outer end portions of a pair of lead wires 4, 5 extending from a pair of respective end hats 2, 3 to protrude outwardly of a tube, respectively, under an airtight condition, and a metallic tubular body 17 having at its large diameter opening end a flange portion 17 to be sealed to an anode tubular body for surrounding the pair of lead wires 4, 5 includes a small diameter tubular extending portion 17b and this extending portion 17b is put and sealed into the stem insulator 16 under an airtight condition. Further, the bottom panel portion 17c mounted to the extending portion 17b has respective holes adapted to have the lead wires 4, 5 inserted thereinto and sets of two resonant elements 18 each of which is adapted to surround each of the lead wires 4, 5 with which each of the sets is combined at high frequencies is mounted on the bottom panel portion 17c. Each of the resonant elements 18 will thereby be each of ring resonant elements displaying respective high impedance properties within a specific frequency band, so that micro-wave components are stopped from being leaked out of the tube.

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 of the cathode body 1, and each end hat 2 and 3.
A pair of lead wires 4 and 5 extending from the lead wire 4
．． A stem insulator 6 that allows the outer end of 5 to protrude out of the tube in an airtight manner.
and an eyelet-shaped metal tube 7 whose one open end surface is brazed to the stem insulator 6. However, the flange portion 7a on the other open end surface of the metal tube body 7 is hermetically sealed to the anode tube 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 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 through hole of each high withstand voltage. It is connected to the center electrode 13 of the type capacitor 12. A metal shield case 14 with a capacitor 12 fixed to its side wall houses 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 includes not only the fundamental wave component of the oscillated microwave but also the second, third, fourth, etc. harmonic components, these leakage outside the device. reliably and efficiently (
It is extremely difficult to prevent it.

In addition, feed-through capacitors are expensive, and LC
Since the filter circuit is held at a cathode potential and the shield case is held at an anode potential (ground), a relatively large shield case is required to prevent sparks between the two, which reduces device size and costs. This was a factor that prevented the reduction.

Means for Solving the Problems In the present invention, a tip-shaped stem insulator is used, and at the flange portion, the stem insulator surrounds a pair of lead wires extending from each of a pair of end hats and goes toward the stem insulator. A metal tube sealed to the anode cylinder is provided with a small-diameter cylindrical extension that penetrates into the stem insulator. The cylindrical extension has a bottom plate portion having a hole through which the pair of lead wires are inserted, and houses a resonant element coupled to the lead wires at least in a high frequency manner. However, the resonant element has a ring-shaped high dielectric constant material through which the lead wire is inserted, and a pair of conductive films attached to both end surfaces of the high dielectric constant material, and one of the conductive films is one of the ring-shaped high dielectric constant materials. Connected to the bottom plate.

Function: With this structure, the small-diameter cylindrical extension penetrates into the stem insulator and acts as a shield, so it is possible to reduce the microwaves that pass through the stem insulator and leak out of the tube. First, the resonant element housed in the armpit resonates with the specific wavelength component of the leaked microwave, and acts as a resonant filter that exhibits high impedance characteristics at the specific wavelength. It becomes possible to simplify or downsize the conventional LC filter circuit and shield case.

Embodiment 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. The ceramic stem insulator 16 is formed in a pot shape to make each outer end of the anode 5 protrude out of the tube in an airtight manner, and the flange 17a to be sealed to the anode cylinder is connected to the large-diameter open end. A metal tube 17 surrounding the pair of lead wires 4.5.
has a cylindrical extension part 17b with a small diameter, and this cylindrical extension part 17
b enters into the stem insulator 16 and is hermetically sealed, and the bottom plate portion 17c provided on this cylindrical extension 17b has holes for the lead wires 4 and 5 to pass through. In addition, two resonant elements 18 are provided on the bottom plate portion 17c to surround each lead wire 4, 5 and couple to it in a high frequency manner. However, the resonant element 18 consists of a ring-shaped high dielectric constant body 18a and a pair of conductive films 18b and 18c attached to both end faces thereof, and the conductive film 18c on the lower face side is brazed to the bottom plate portion 17c. . The high dielectric constant body 18a is made of ceramic having a dielectric constant ε of 30 to 90, and the pair of conductive films 18b and 18c are each made of a two-layer structure in which a plating layer is stacked on a metallized layer. Further, the depth h of the cylindrical extension portion 17b is set to an electrical length that approximately matches one natural number of the wavelength of the arbitrary harmonic component of the oscillated microwave.

The conductive film 18b on the upper surface side of each resonant element 18 is not in contact with the lead wire passing through the resonant element, but the specific wavelength component of the microwave leaked to the stem insulator 16 side through the lead wire 4.5. resonates with the resonant element 18. That is, since the resonant element 18 becomes a ring resonator exhibiting high impedance characteristics in a specific frequency band, leakage of the microwave component outside the tube is prevented. Moreover, the cylindrical extension part 17b
acts as a shield, thereby reducing the microwave transmission area of the stem insulator 16. Furthermore, the cylindrical extension 1
The choke action of 7b can also attenuate specific harmonic components 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 plays the role of a capacitor due to its high dielectric constant, and is connected in parallel to a conventional feedthrough capacitor, so in addition to the effects described in the previous embodiment, This has the advantage that feedthrough capacitors can be eliminated or miniaturized.

In the embodiment shown in FIG. 3, the high dielectric constant material 1 of the resonant element 18
8a has a protrusion on the lower surface, and this protrusion is connected to the bottom plate portion 17.
By fitting into the hole c, the effect of regulating the position of the resonant element 18 is obtained.

Effects of the Invention According to the present invention, as described above, not only can leakage of microwaves be efficiently blocked within the tube of the magnetron, but also leakage of microwaves can be effectively prevented within the stem insulator by the cylindrical extension of the metal tube held at an anode potential (ground). This makes it possible to simplify the LC filter circuit and downsize the circuit components and shield case.

[Brief explanation of the drawing]

1 to 3 are side sectional views of a magnetron cathode assembly embodying the present invention, and FIG. 4 is a side sectional view of a conventional magnetron cathode assembly. 1... Cathode body, 2, 3... End hat, 4゜5... Lead wire, 16...
Stem insulator, 17...Metal tube body, 17b...
...Cylindrical extension part, 17c...Bottom plate part, 1
8...Resonant element. Name of agent: Patent attorney Shigetaka Kurino and 1 other person f-7'Kuraiki Fufufu2.3-Ichigo, NVhe-,1-Ki,5-,Lee VI fC-11 Stem #f! t & l t17--Kin 4 Suga-ki 17b-Issho-en-yu-shu 17C-Hirehara wholesale public Ig--Tahi 41 Poor 1 (To IBLIk-= J't14

Claims (1)

[Claims] A flange that surrounds a pair of lead wires that extend from each of 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 body. The metal tube body has a small-diameter cylindrical extension that penetrates into the stem insulator, and the cylindrical extension has a bottom plate with a hole through which the pair of lead wires are inserted. A resonant element coupled to the lead wire at least in a high frequency manner is accommodated, and the resonant element includes a ring-shaped high dielectric constant material through which the lead wire is inserted, and attached to both end surfaces of the high dielectric constant material. 1. A cathode assembly for a magnetron, comprising a pair of conductive films, one of the conductive films being connected to the bottom plate portion.