JPS6047761B2 - airtight high frequency window - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an airtight high frequency window provided between a vacuum section and an external waveguide in a microwave tube such as a traveling wave tube or a klystron.

A microwave tube such as a traveling wave tube or klystron consists of an electron gun that emits an electron beam, a collector that captures the electron beam, a microwave amplification section that amplifies the microwave through interaction with the electron beam, and a microwave amplification section. It consists of an input/output coupling section that connects with an external waveguide, and the input/output coupling section maintains airtightness inside the microwave tube and also has airtightness to allow microwaves to pass through with as little loss as possible. A high frequency window is used.

However, if the airtightness of the airtight window is insufficient, the degree of vacuum of the microwave tube will naturally deteriorate, resulting in a decrease in performance and a shortened lifespan of the microwave tube. Figure 1 shows a conventional general airtight high frequency window.
In the figure, a circular waveguide 2 is formed between an output waveguide 1 and an external waveguide 3, and a dielectric disk 4 is hermetically brazed in the middle of the circular waveguide 3.

That is, airtightness is maintained only by the circumferential surface brazing portion 5 of the dielectric disk 4. In such a conventional hermetic window structure, the operating frequency is high, and therefore the dielectric disk 4
If it is necessary to reduce the thickness of the disc, the vacuum sealing surface around the disk will have a smaller area, which weakens the mechanical strength of the joint surface and has the disadvantage that sufficient airtightness cannot be maintained reliably. Ta. In order to eliminate such drawbacks of the circumferential surface joint, an airtight window as shown in FIG. 2 has been proposed.

In FIG. 2, metallized layers 6 and 7 are formed on both sides of the peripheral edge of the dielectric disk 4 and on the circumference, and a circular waveguide 8 with a flange Ba) 9a is formed on the metallized layer 6 on the peripheral edge. 9 are brazed to each other to maintain airtightness between the output waveguide 1 and the external waveguide 3. With this structure, even if the dielectric disk 4 is guided, the length of the sealing part can be increased,
Compared to the conventional example shown in FIG. 1, the airtightness inside the microwave tube can be maintained to a high degree. By the way, after conducting various investigations on airtight windows with the structure shown in Figure 2, we found that although they may have a seemingly similar structure, in some cases they have very good high-frequency characteristics.
In some cases, it was observed that abnormal heat generation or airtight failure occurred7. After further investigation, it was discovered that the cause of the above-mentioned variation in properties was the length of the brazed portion in the radial direction. The present invention was made based on the new recognition of the variation in the characteristics of airtight windows due to double-sided brazing of the peripheral edge of the dielectric disk as described above, and it is possible to improve the microwave transmission characteristics and maintain airtightness. The aim is to provide a sufficiently reliable high-frequency window.
There is. The airtight high frequency window of the present invention has a radius R2 of the dielectric disk.
The difference R2-R1 between the radius R1 of the circular waveguide and the radius R1 of the circular waveguide is set to be approximately an integral multiple (NXI2) of the propagation half wavelength.

The present invention will be described in detail below with reference to FIG.

In FIG. 3, as in the case of FIG. 2, the dielectric disk 4 has metallized layers 7 and 6 formed at its circumferential portion and the joint portion with the flange, respectively, so that these portions are It forms a radial line whose outer ends are short-circuited. Therefore,
The impedance Z when looking from the inside to the outside of the flanges 8a and 9a is greatly influenced by the difference between the outer radius R2 of the dielectric disk 4 and the inner radius R1 of the circular waveguide 8, R2-R1. It is clear that the most ideal condition is when λ is the operating wavelength and n is a positive integer, that is, the impedance when looking outward from the inside of the flanges 8a and 9a is zero.

In this case, the portion surrounded by the metallized layer is equivalent to being short-circuited in terms of high frequency due to the so-called choke effect, and problems such as abnormal heat generation and leakage of airtight do not occur. At this time, it should be noted that since the inside of the radial line is composed of a high dielectric material, there is a so-called wavelength reduction effect.
The actual size (electrical length) that satisfies the above conditions is surprisingly small. As an example, the dimensions of a high frequency window used in the 14 GHz band are as follows when a dielectric material with a relative dielectric constant of 9.2 is used.

Of course, when determining the final dimensions of the high frequency window, in addition to R1 and R2, the thickness of the dielectric disk or the third
Dimensions 1, etc. of the circular waveguide 8 shown in the figure must be selected paying attention to the resonance frequency of ①SWRl. By employing the present invention, abnormal heat generation or airtight failure of this type of high frequency window, which has occasionally been experienced in the past, has been prevented from occurring. Brief Description of the Drawings Figure 1 is a cross-sectional view of a conventional airtight high-frequency window with dielectric disk circumferential surfaces brazed, and Figure 2 is a cross-sectional view of a conventional airtight high-frequency window with dielectric disk circumferential sides brazed on both sides. The cross-sectional view, FIG. 3, is a cross-sectional view of one embodiment of the present invention.

DESCRIPTION OF SYMBOLS 1...Output waveguide, 3...External waveguide, 4...Dielectric disk, 6...Peripheral metallized layer, 7... ...Circumferential metallization layer, 8 and 9...
・Circular waveguide, 8a and 9a...flange.

Claims (1)

[Claims] 1. A dielectric disk having metallized layers formed on both sides of the peripheral edge and the circumferential surface, and a flanged circular waveguide brazed to the metallized layers on both sides of the peripheral edge of the dielectric disk. In the airtight high frequency window, the difference between the radius of the dielectric disk and the radius of the circular waveguide is approximately λ with respect to the operating wavelength λ.
An airtight high-frequency window characterized by having an electrical length that is an integral multiple of /2.