JPH0134486B2 - - Google Patents

Description

Detailed Description of the Invention (Industrial Application Field) The present invention converts the propagation mode of electromagnetic waves propagating through a waveguide from a circular waveguide mode to a rectangular waveguide mode to a free space plane wave and radiates it. The present invention relates to a mode conversion radiator that can efficiently convert and radiate high-power microwave and millimeter wave propagation modes.

(Prior art) Conventional mode converters that convert waveguide propagation modes of microwaves and millimeter waves are limited to those for communication with low-power electromagnetic waves; A mode converter that can be used to convert the propagation mode in an oversized waveguide that can be used to propagate high-power electromagnetic waves such as high-power millimeter waves used for extremely high temperature heating of plasma in a fusion tokamak device is at least the present invention. As far as I know, it is still in the development stage.

(Problems to be Solved by the Invention) In particular, regarding the generation of high-power millimeter waves for heating in the above-mentioned nuclear fusion tokamak device, in the recently developed high-power electron tube Gyrotron as a source of high-power millimeter waves, Because high-power millimeter waves are generated by rotating electrons using a magnetic field, the oscillation output millimeter waves must be extracted in circular waveguide mode.On the other hand, plasma is generated by millimeter waves in a nuclear fusion tokamak device. When heating by concentrated irradiation, it is necessary to radiate millimeter waves in a linearly polarized propagation mode. Therefore, regarding the mode converter used in this type of high power mode conversion radiator,
There has been a strong desire to develop a high-power circular mode-linear polarization mode converter that converts the circular waveguide mode into a linearly polarized propagation mode or a rectangular waveguide mode.

Moreover, as mentioned above, in high-power millimeter-wave transmission systems, oversized waveguides that must be used are not suitable for communications because multiple different propagation modes can coexist. In addition, there was also a problem in that the conventional mode converter for low power communication could not be used for high power at all in terms of power durability.

(Means for Solving the Problems) An object of the present invention is to solve the problems in response to the above-mentioned conventional demands, to withstand the transmission of high-power electromagnetic waves, and to transform the circular waveguide mode to the linearly polarized propagation mode. A mode conversion radiator for high power that can efficiently perform mode conversion and radiation into a rectangular waveguide mode, in particular a circular waveguide TE _pn mode (m=
1, 2,...) into linearly polarized TEM mode or rectangular waveguide TE ₁₀ mode. heating, measurement,
The object of the present invention is to provide a mode conversion radiator for high power required for control and other microwave heating applications.

That is, the mode conversion radiator of the present invention consists of a cylindrical waveguide each having a cross section of a size that includes a cylindrical waveguide, and a radiator having a length approximately equal to the product of the inner diameter of the cylindrical waveguide and the cocution of the electromagnetic wave propagation angle. A cylindrical waveguide and a rectangular waveguide with an opening at the other end so as to emit electromagnetic waves with the same phase are connected and arranged in sequence with their respective central axes, confocal axes, and central axes aligned. Accordingly, the electromagnetic wave in the circular waveguide mode is converted into a free space plane wave and then radiated.

(Example) The present invention will be described in detail below with reference to the drawings.

First, an example of the basic configuration of a circular-to-square mode converter, which constitutes a main part of the mode conversion radiator of the present invention, is shown in FIGS. 1a to 1c. Note that Figure 1a is a top view, and Figure 1b is a top view.
is a side view, and c is a front view. The circular-to-square mode converter with the basic configuration shown in the figure includes a cylindrical waveguide 1 with an inner diameter a, a short axis inner diameter b and a long axis inner diameter 2b.
A circular TE _pn is formed by vertically connecting a parabolic waveguide 2 with a rectangular waveguide 3 having an inner short side c and an inner long side d.
→It is designed to perform mode conversion of rectangular TE _2n,p . The parabolic waveguide 2, which forms the main part of this basic configuration, is a combination of two parabolic mirrors facing each other so that their focal axes coincide and become common. The common focal axis is made to coincide with the central axis of the cylindrical waveguide 1. Generally, such a parabolic waveguide 2
The lateral width, that is, the minor axis inner diameter b, may be selected to be larger than the inner diameter a of the cylindrical waveguide 1, but for the sake of simplicity, in the following description, an example will be described in which a=b.

Therefore, the axial length l of the parabolic waveguide 2
is set so that l=a cot α. Note that α in the above equation is the propagation angle of electromagnetic waves within the cylindrical waveguide 1, and is given by α=sin ⁻¹ (ρ′ _pn V _c /πf·a) radians. Here, ρ' _pn is the m-th root of the Betzel function J _p '(ρ)=0, V _c is the speed of light, and f is the frequency of light.

On the other hand, the size of the cross section of the rectangular waveguide 3 shown in FIG.

Furthermore, the appearance of the electric field in the TE ₀₁ mode in the cylindrical waveguide 1 is shown in Fig. 2, and the traveling direction of the elementary plane wave in the electromagnetic wave mode in the cross section of the parabolic waveguide 2 is shown in Fig. 3. put.

What has been described above is the basic configuration of the circular-to-square mode converter which constitutes the main part of the present invention, and the configuration can be made with various modifications as described below, if necessary.

For example, the purity of the output mode can be improved by suppressing the occurrence of multiple reflections near the peak of the parabolic waveguide 2 due to the direct connection between the cylindrical waveguide 1 and the parabolic waveguide 2 in the basic configuration described above. The overall structure of a wedge-shaped cylindrical waveguide inserted between the cylindrical waveguide 1 and the parabolic waveguide 2 is shown in FIG. The configuration of the cross section taken along line A-A' is shown in part b, and the configuration of the cross section taken along line B-B' is shown in part c of the same figure. In the illustrated overall configuration, a cylindrical waveguide 6 and a parabolic waveguide 9 are used.
A wedge-shaped cylindrical waveguide 7 is inserted between the cylindrical waveguide 7 and the cylindrical waveguide 7. Inside the cylindrical waveguide 7 are two wedge-shaped conductor pieces 8 and 8' that open from the tube axis toward the side wall. are inserted facing each other, and the wedge-shaped opening angle V is as shown in FIGS. 4b and 4c, respectively.
It is continuously and gradually changed from a minimum value of 0° at the input end connected to the cylindrical waveguide 6 to a maximum value of 2 (90°-φ ₀ ) at the output end connected to the parabolic waveguide 9.

Next, the mode conversion radiator of the present invention is a circular-to-square mode converter having the basic configuration shown in FIG. The rectangular waveguide 3 in the basic configuration shown in FIG. 1 has its output end as shown in FIG. The rectangular waveguide 4 is cut diagonally at an inclination angle θ to provide an aperture 5, and the electromagnetic waves propagating in a zigzag manner in the oversized rectangular waveguide are cut diagonally to form an aperture surface. For example, it is suitable for the electromagnetic wave irradiation during plasma heating mentioned above to convert it into a linearly polarized TEM mode and radiate it. Note that the above-mentioned inclination angle θ of the aperture is set to θ=sin ⁻¹ (m V _c /f·c) radians. Here, θ is the angle between the normal to an elementary plane wave in the rectangular waveguide and the tube axis.

Next, the output aperture surface provided in the rectangular waveguide 3 in the basic configuration shown in FIG. 1 is used instead of being obliquely inclined as shown in FIG.
The sixth example shows a configuration of a bent rectangular waveguide with an aperture that converts TE ₂₀ mode to TE ₁₀ mode.
Shown in Figures a-c. In addition, the same figure a shows the upper surface, and the same figure b and c show the cross section before and after bending. The bent rectangular waveguide having the configuration shown in the figure is constructed such that the tube axis intersects a rectangular waveguide 12 with an inner side length c and a rectangular waveguide 13 with an inner side length c' having an opening 15 at an angle β. Each rectangular waveguide 12
When the angles that the elementary plane wave normals in and 13 make with the respective tube axes are θ and θ′, respectively,
The bending angle β is set to approximately β=θ−θ′=1/2cos ⁻¹ (sin ² θ/m+cos 2θ) radians. Here, m is the propagation mode order of the circular TE _pn in the cylindrical waveguide 1.
Note that the optimal bending angle β is determined experimentally, for example.

Next, the output aperture surface provided in the rectangular waveguide 3 in the basic configuration shown in Figure 1 is tilted to create a waveguide suitable for use instead of converting the rectangular TE ₂₀ mode in the tube into a linearly polarized TEM mode. An example of the configuration of a circularly curved rectangular waveguide is shown in FIGS. 7a and 7b. Note that figure a shows the top surface, and figure b shows the side surface. In the circularly curved rectangular waveguide 10 having the illustrated configuration, a partition plate 11 is inserted into the center of the pipe parallel to the E plane, and is curved to form a part of the circle in the H plane. When a rectangular TE ₂₀ mode electromagnetic wave with m = 1 of the circular TE _pn mode is incident on the waveguide 1, the input electromagnetic wave is divided into two by the partition plate 11, and the width formed on the left and right sides of the partition plate 11 is Each wave propagates independently in the TE ₁₀ mode in the a/2 rectangular waveguide. Therefore, in the TE ₂₀ mode at the time of incidence, the a/2
The directions of both electric fields in the double-width waveguide are reversed, and the electromagnetic waves propagate in opposite phases to each other, but the bending angle δ of the circularly curved rectangular waveguide 10 is expressed as δ=1/√( ^{2 2} _c ² )-1 radian, at the output aperture surface provided at the other end of the rectangular waveguide 10, there will be a difference in the propagation path length within the waveguide between the inside and outside of the bend, so the partition plate 1
The directions of the electric fields in both waveguides configured on the left and right sides of 1 are aligned. Therefore, the electromagnetic wave radiated from this output end opening becomes a quasi-TEM wave having a polarization plane parallel to the partition plate 11.

In the mode conversion radiator of the present invention configured as described in detail above, when high-power millimeter waves in the circular TE _pn mode generated from the high-power millimeter-wave oscillator tube gyrotron described above are incident from the cylindrical waveguide 1, The electromagnetic waves converted into the rectangular TE _2n,0 mode are radiated as a plane wave from the inclined aperture of the rectangular waveguide 3, for example, and the high-power millimeter waves of the plane wave generate plasma in the fusion tokamak device. It can be irradiated directly, or it can be irradiated by high-power millimeter waves in TE ₁₀ mode radiated from the next stage rectangular waveguide connected in an inclined manner, for example, the rectangular waveguide 13 shown in Fig. 6. Plasma can also be directly irradiated. In addition, such a plane wave or square wave
Using the TE ₁₀ mode, the plasma can be irradiated with electromagnetic waves having a constant plane of polarization.

FIG. 8 shows a specific example of the configuration of the main parts of the mode conversion radiator of the present invention having such an effect when operated at a frequency of 35.5 GHz, for example. In the illustrated configuration example, a parabolic waveguide 17 with a length of 97 mm is circumscribed and cascaded to a cylindrical waveguide 16 with an inner diameter of 32.5 mm, and the parabolic waveguide 1
A rectangular waveguide 18 having inner dimensions of 32.5 mm x 65.0 mm is circumscribed and cascaded to 7. In the mode conversion radiator of the present invention having such a configuration, the frequency is 35.5 GHz.
The electromagnetic wave is transmitted through the cylindrical waveguide 16 in circular TE ₀₁ mode.
When the output end of the rectangular waveguide 18 is cut at an angle θ=10.6° to provide an inclined opening, a planar electromagnetic wave is radiated in a direction making an angle of 10.6° with respect to the tube axis. .

In addition, a wedge-shaped cylindrical waveguide having the configuration shown in FIG. V (= 2 (90° - φ ₀ )) as φ ₀ = 60° and 60
If the mode conversion radiator of the present invention is selected as 70%, the conversion efficiency of the mode conversion radiator of the present invention can be improved from about 70% to about 90% when the cylindrical waveguide end 16 is directly cascaded to the parabolic waveguide 17. can.

Furthermore, a circularly curved double rectangular waveguide having the configuration shown in _FIG .
Frequency 35.5G when converting to TEM mode
The inner width a of the rectangular waveguide 18 is 32.5 mm for Hz.
The bending angle δ is 15.4°, and the radius of curvature d is 20cm.
The desired planar electromagnetic wave was obtained when selecting the desired planar electromagnetic wave.

(Effects of the Invention) As is clear from the above description, according to the present invention, the following remarkable effects can be obtained.

(1) As a converter for electromagnetic wave propagation mode in a waveguide,
Since the configuration is extremely simple, there is little conversion loss, and there are no extreme discontinuities, so
It is difficult to cause discharge during propagation of high-power electromagnetic waves, and is suitable for use in high-power millimeter wave transmission.

(2) Since the mode converter can be configured to be completely sealed, unnecessary electromagnetic waves are not emitted to the outside, and it is safe even when used for high-power millimeter wave transmission.

(3) Since the mode conversion radiator used to transmit and radiate high-power electromagnetic waves can be configured in a small size, the overall configuration of the device is complex, such as a nuclear fusion tokamak device, and the shape of each part itself is also complex. It can also be easily used for.

[Brief explanation of drawings]

Figures 1a, b, and c are top, side, and front views respectively showing an example of the basic configuration of a circular-to-square mode converter that forms the main part of the present invention, and Figure 2 is a top view, a side view, and a front view of an example of the basic configuration of the circular-square mode converter that forms the main part of the present invention. FIG. 3 is a cross-sectional view showing the electric field in the cylindrical waveguide, FIG. 3 is a cross-sectional view showing the propagation direction of an elementary plane wave in the parabolic waveguide in its basic configuration, and FIG. A perspective view showing a configuration example of a wedged cylindrical waveguide inserted between a cylindrical waveguide and a parabolic waveguide in the same basic configuration, and the line A-A' and the line in the same figure. 5a, b, and c are top views, side views, and front views, respectively, showing configuration examples of the rectangular waveguide in the mode conversion radiator of the present invention; Figures 6a, b, and c are top views respectively showing configuration examples of a bent rectangular waveguide used as a rectangular waveguide in the mode conversion radiator of the present invention, and lines A-A' and 6 before and after the bending. Figures 7a and 7b are cross-sectional views showing the cross-sectional shape of line B-B', respectively, and show an example of the configuration of a circularly curved rectangular waveguide used in place of the rectangular waveguide in the basic configuration shown in Figure 1. A top view and a side view are shown, respectively, and FIG. 8 is a cross-sectional view showing an example of a specific configuration of the mode conversion radiator of the present invention. 1, 6, 16... Cylindrical waveguide, 2, 9, 17... Parabolic waveguide, 3, 4, 12, 13, 18... Rectangular waveguide, 5, 15... Opening, 7... Wedge cylinder waveguide,
8, 8'... Wedge-shaped conductor piece, 10... Circularly curved rectangular waveguide, 11... Partition plate, 14... Connection surface.

Claims (1)

[Scope of Claims] 1. A cylindrical waveguide, each having a cross section of a size that is sequentially included, and a parabolic waveguide having a length approximately equal to the product of the inner diameter of the cylindrical waveguide and the cutoff of the electromagnetic wave propagation angle. By sequentially connecting and arranging a wave tube and a rectangular waveguide with an opening at the other end so as to emit electromagnetic waves with the same phase, with their central axes, confocal axes, and central axes aligned, A mode conversion radiator characterized in that it is configured to convert an electromagnetic wave in a circular waveguide mode into a free space plane wave and radiate it. 2. The cylindrical waveguide is connected to the cylindrical waveguide through a cylindrical waveguide in which two wedge-shaped conductors, which open toward the tube wall from the tube axis and whose opening angle increases sequentially along the tube axis, are inserted facing each other. 2. The mode conversion radiator according to claim 1, wherein the mode conversion radiator is connected to the parabolic waveguide. 3 The opening surface of the rectangular waveguide is relative to the tube axis,
3. The mode conversion radiator according to claim 1, wherein the rectangular waveguide has an angle substantially equal to an angle made by the normal to the plane wave in the tube with the tube axis. 4. By connecting two rectangular waveguides obliquely so that their respective tube axes intersect at an angle that is approximately equal to the difference between the angles that the normal plane waves in each tube make with their respective tube axes, The mode conversion radiator according to claim 1 or 2, characterized in that the rectangular waveguide is configured. 5 A cylindrical waveguide each having a cross section of a size that is sequentially included, a parabolic waveguide with a length approximately equal to the product of the inner diameter of the cylindrical waveguide and the cutoff of the electromagnetic wave propagation angle, and approximately A rectangular waveguide with a partition plate inserted in the center parallel to the E plane and an opening at the other end that is curved to form part of a circle in the H plane and emits phase-aligned electromagnetic waves. A mode characterized in that the electromagnetic waves in the circular waveguide mode are converted into free space plane waves and radiated by sequentially connecting and arranging the respective central axes, confocal axes, and central axes to coincide with each other. Conversion radiator.