JPS63131701A - Circular waveguide mode converter with stepwise periodic structure - Google Patents

Abstract

PURPOSE:To remarkably facilitate the manufacture by using a circular waveguide interposing discontinuous part whose guide diameter is increased/ decreased repetitively stepwide at a prescribed period over a prescribed range so as to apply the conversion of electromagnetic wave transmission mode between the TEon mode and the TEom mode. CONSTITUTION:Two kinds of circular waveguides having a length (l) whose radius is changed as a single step by + or -DELTAa at the middle of the circular waveguide having a radius (a) acting like an oversize waveguide with respect to a wavelength of an electromagnetic wave to be sent are formed while the plural discontinuous parts are connected in cascade alternately with the center axis coincident with each other. Actually, two kinds of circular waveguides having a length (l) and radii of a+DELTAa and a-DELTAa may be manufactured by fitting them coaxially. Moreover, the inner circumferential face of the cylinder conductor having a thickness whose radius is not in excess of a-DELTAa is processed and manufactured by means of, e.g., a boring lathe. Thus, the structure is simplified and the design/manufacture is facilitated considerably.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention describes the transmission mode of electromagnetic waves by a circular waveguide in TE
TEo converting between on mode and TEo mode;
.

- Regarding the TEon mode converter, in particular, the periodic structure of the inner circumferential wall surface of the circular waveguide is improved in stages to facilitate its design and manufacture.

(1. Prior Art) Conventionally, one type of heating method for the fused plasma is direct heating using the output of a high-power gyrotron. Therefore, the high frequency band microwave output from the gyrotron is extracted in the TEon mode centered on the circular waveguide TEoz, but for heating, control, and measurement of fusion plasma, the 1]E mode is It is advantageous to use linearly polarized microwaves such as Therefore, conventionally, the circular waveguide TEoz mode output of the gyrotron is ↑
Generally, the E61 mode is converted into a linearly polarized wave of the 11Ez mode.

Furthermore, a circular waveguide mode converter between TEaz mode and TEc+ mode has been commonly used as a simple oversized mode converter at the laboratory level.

(Problems to be Solved by the Invention) Conventionally, as a circular waveguide TEon1-TEon mode converter for high power use in high frequency bands such as microwaves and millimeter waves, I
nt, J, Electron Magazine, Vol. 57, 1984, pp. 1225 to 1246, a circular waveguide TE with a sinusoidal periodic structure.

- TEon mode converters were used exclusively. This mode converter changes the radius of the inner peripheral wall surface of the circular waveguide in a sinusoidal manner with a period equal to the heat wavelength between the TEo mode and the TEon mode, as will be described in detail later. By passing through the discontinuous portion of the periodic structure, mode conversion between TEon and TEon is performed.

However, processing and manufacturing to accurately change the radius of the inner circumferential wall surface of a circular waveguide into a sinusoidal shape as designed requires advanced technology and equipment, and is not only difficult.
To find the dimensions and shape of the optimum values that will actually yield the highest conversion efficiency based on the design values obtained as described below,
The problem is that it requires an enormous amount of calculation to determine the conditions under which the required electromagnetic wave component is maximized by approximating a sine wave into an extremely large number of minute steps, and as a result, only an approximate solution can be obtained. Ta.

(Means for Solving the Problems) An object of the present invention is to solve the above-mentioned conventional problems, to be easy to design and manufacture, and to make calculations for optimizing design values relatively simple. Circular waveguide TEo, -TEo, consisting of discontinuous parts of a periodic structure such that a strict piece is obtained
An object of the present invention is to provide a mode converter.

That is, the stepped periodic structure circular waveguide mode converter of the present invention is a circular waveguide with a discontinuous portion in which the pipe diameter repeatedly increases and decreases in at least one step at a predetermined period over a predetermined range. Consisting of tubes, TE.

The present invention is characterized in that the electromagnetic wave transmission mode is converted between the modes TEo and TEo.

(Function) Therefore, according to the present invention, the periodic structure has a simpler structure than the conventional one, is much easier to design and manufacture, and can reliably and easily optimize design values. It is possible to realize a circular waveguide mode converter with

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

First, FIG. 1 schematically shows an example of the simplest configuration of a circular waveguide mode converter with a stepped periodic structure according to the present invention, which has a square wave periodic structure with only one step forming the periodic structure. The illustrated configuration example has a circular waveguide with radius a that acts as an oversized waveguide for the wavelength of electromagnetic waves to be transmitted, and a length β in the middle of which the radius is changed by ±Δa in a single step shape. It is constructed by interposing discontinuous parts in which two types of circular waveguides are connected in cascade alternately in multiple stages with their central axes coincident, and actually have lengths with radii a + Δa and a - Δa, respectively. It can also be manufactured by coaxially fitting two types of circular waveguides (1 and 1), and the inner peripheral surface of a thick cylindrical conductor with a radius not exceeding a - Δa can be manufactured using a boring lathe, etc. It can also be manufactured by processing.

The deviation value Δa of the waveguide radius and the section length l in the above configuration example are as shown in FIG. 2, as shown in FIG. By approximation from the converter, the amount of deviation of the radius and the half period length of the repetition deviation, which are obtained as described later for the discontinuity of the sinusoidal periodic structure, are used as initial values in the design of the radius deviation value Δa and the interval length l, respectively. As described below, optimization calculations using a mode matching method are performed using a computer, and optimal design values that provide the highest conversion efficiency are determined.

In other words, we will omit the details of the calculation process that was presented at an academic conference earlier, but the behavior of electromagnetic wave propagation at the discontinuous part of the circular waveguide shown in Figure 1 can be calculated using the radius of the circular waveguide. The scattering determinant is obtained by analyzing the transmitted power and reflected power using a mode matching method when the electromagnetic field is continuous even though the propagation mode is different before and after a step-like discontinuous surface where the field changes suddenly. Find as,
When such discontinuous surfaces are connected in multiple stages, the total transmitted power and reflected power are calculated as a cascade of scattering determinants, and the radius deviation value Δa and section length l described above are gradually changed from their initial values. While the above-mentioned total transmitted power and reflected power are repeatedly calculated, the radius deviation value Δa and the section length l when the highest conversion efficiency is obtained where the transmitted power is maximum and the reflected power is minimum are respectively calculated. The optimum design value of

Therefore, the above-mentioned initial values used as the starting point for optimizing the above-mentioned design values for the radius deviation value Δa and section length l of the discontinuity in the circular waveguide mode converter of the present invention are different from those of the conventional sinusoidal periodic structure. It is determined as follows using the calculation method disclosed by Thumm (M.) for a circular waveguide mode converter.

As shown in FIG. 3, with respect to the average radius a0 in the circular waveguide discontinuity having a sinusoidal periodic structure, the tube axis direction Z
Let Δa be the deviation of the radius a (z) which is a function of Coupling between transmission modes occurs in the continuum, which acts as a mode converter.

Thus, the heat wavelength λβ equal to the period length of the radial shift is TE. The phase constants of the 7 mode and TEon mode are β, respectively. 7 and β. , it can be determined by the following equation (11).

On the other hand, the radial deviation amount Δa is determined from the following equation (2) expressing the radius a (z) which is a function of the tube axis direction Z, as described above.

a(z)=a0(1+εsin (2π2/λβ))
(2) In the above equation (2), ε is the number of repetitions of the radial shift period forming the periodic structure of the discontinuous part, which is usually selected appropriately in the range of 3 to 6, and the total length of the discontinuous part is L = Assuming N·λβ, it is given by the following equation (3).

ε= (312
・NC, a. 1 Here, CON +. is expressed by the following equation (4) using the n-th and m-th zero points ρIn and ρ other than 0 in the −th order Betzel function J.

By approximation from a sinusoidal periodic structure, the initial values of the radius deviation value Δa and section length l in the step-like periodic structure circular waveguide mode converter of the present invention are set to the following equation (5).

2β Δa=ε・atr, l= (
5) Starting from the initial values set in this manner, the radius deviation value Δa and the interval length l are subjected to the optimization calculations described above to find the optimal design values that provide the highest conversion efficiency.

In the above configuration example, the deviation value from the average radius a0 of the circular waveguide in the stepped periodic structure was vertically symmetrically increased or decreased to ±Δa, but the highest conversion efficiency obtained as a result is practically practicable. As long as it is 90% or more, it does not necessarily have to be symmetrical; for example, if there are restrictions due to the pipe diameter standards of two types of waveguides that are made to fit alternately to form a stepped periodic structure, etc. In this case, two types of circular waveguides with standard pipe diameters close to the optimal design value obtained as described above are used, and only the section length l of the stepped periodic structure is set to the optimal design value. It is also possible to do so.

When an electromagnetic wave in the circular TEon mode is incident from one of the circular waveguides connected to the stepped periodic structure circular waveguide mode converter of the present invention according to the configuration example shown in the first diagram configured as described above, the electromagnetic wave is transmitted. The mode TE,n changes into various modes at the discontinuous portion of the stepped periodic structure. However, in a coaxial circular waveguide, only the electromagnetic waves in the circular TE, Since the radius a (z) of the circular waveguide exhibits a periodic change of approximated period length, only the desired circular TE, imode electromagnetic waves are extracted from the other circular waveguide, and the TEon mode - TEol
Mode conversion between 11 modes is achieved.

In the configuration example shown in the first diagram, according to the present invention, the step-like periodic structure that periodically changes the radius of the circular waveguide is increased or decreased by only a single step, and is made into a square wave-like periodic structure, but the sine-wave periodic structure A step-like periodic structure with multiple steps can be obtained by approximation from In any case, it is of course possible to find the optimum design values for a single-stage stepped periodic structure using the same mode matching method as described above. Therefore, in any case, although it is based on approximation from a sinusoidal periodic structure, it is an optimization of the design value for a stepped periodic structure with a finite number of stages, so it is an optimization of the design value of the sinusoidal periodic structure itself. In contrast to this, which requires a huge amount of calculation due to countless minute step-like approximations and can only obtain an approximate solution, it is possible to obtain the optimal design value as an exact solution with a much smaller amount of calculation.

Next, specific numerical examples of the stepped periodic structure circular waveguide mode converter of the present invention will be explained.

(1) Circular TEOI-TE+ with frequency 35.5 GHz
12 mode converter.

FIG. 4 shows a concrete numerical example of the structure of a circular TEo+=TEoz mode converter in an oversized waveguide system with a frequency of 35.5 GH2 and a waveguide radius of 16 mm. In the illustrated example, the heat wavelength λβ between the TEon mode and the TEoz mode is 60.8 m, and when the number of repetitions of the radial shift period N = 4, the deviation amount Δa for the average radius a = 16 m is 1. It becomes 28wm. Therefore, considering the ease of obtaining the material waveguide and the ease of processing, the deviation value Δa of the radius was set to +1. We decided to adopt material waveguides with radii of 17+n and 14.5n with ON and -1,5 dragons, and set the periodic length 21 of the stepped periodic structure to the above-mentioned initial value λβ = 60.8 Optimal starting from Tsuru. The period length was set to 2J = 59.7m. A circular waveguide with a radius of 16 mm is connected before and after the discontinuous portion of such a structure, and connecting flanges are attached to both ends of the circular waveguide.

The power ratios of transmitted power and reflected power for each transmission mode in the above specific example are shown for initial values and optimal design values, respectively, as shown in Tables 1 and 2 below, and the mode conversion efficiency obtained by the initial values is shown in Tables 1 and 2 below. is about 85%
On the other hand, the mode conversion efficiency obtained with the optimal design value was improved to about 93%', and the actual measurement results were also almost the same. Based on the same initial values, the mode conversion efficiency in a conventional mode converter with a periodic sinusoidal structure is approximately 90%, and if optimization is performed using the approximation described above, it is expected to reach approximately 97%. However, as a mode converter, a conversion efficiency of 90% is sufficient for practical use, so conventionally, mode converters with a sinusoidal periodic structure do not require an extremely large amount of calculations and optimization. Design and production were carried out based on initial values, but
In addition to requiring considerable technology for precision machining, there was a problem in that if the actually manufactured product deviated from the design values, the desired mode conversion efficiency could not be obtained.

Table 1 Table 2 (2) Frequency 56 G11z circular TfEoz-TIi
a+ mode converter.

FIG. 5 shows a concrete numerical example of the structure of a circular TEoz→TEo+ mode converter in an oversized waveguide system with a frequency of 56 GHz and a waveguide radius of 12.8 m. In the illustrated example, the average radius ao = 12.2, the optimum deviation amount Δa for carving on the fin is ±0.6 mm, and the radius is 13.4 m.
Using material waveguides of 12.2 mm and 12.2 mm, a stepped periodic structure with a period length of 64.6+n is repeated for 5 cycles, and connection flanges are attached to the circular waveguides at both ends.

Table 3 shows the power ratio of transmitted power and reflected power for each transmission mode in the above-mentioned specific example with respect to the optimal design value, and the mode conversion efficiency obtained with the initial value is about 95%. , the mode conversion efficiency obtained with the optimal design values is improved to about 98%.

Table 3 Design values for the mode converter of the present invention In order to verify the above-mentioned optimization results, for example, the above-mentioned specific numerical example (
For 11 circular TE6+=TEoz mode converters, when the number of repetitions N of the radial shift period of the stepped periodic structure is increased sequentially, electromagnetic waves are radiated into the air from the discontinuous end face opening, and the respective far-field radiated electric field strengths are calculated. The measurement result is expressed as TEon(m=1.2.3
) The power of each propagation mode was calculated by determining the absolute value of the amplitude of the electromagnetic wave in the mode IAnI.

are the polar coordinates of the point and Eψ are the nine components of the far radiation electric field with respect to the radiation aperture end face coordinate angle ψ.

The schematic arrangement of the far-field radiation electric field measurement system described above is shown in FIG. 8 and 9, respectively.

In the measurement system shown in FIG.
5.5 G11z electromagnetic waves are sequentially supplied to the variable attenuator 4 via the reflected wave absorption circulator 2 and the frequency meter 3 to adjust the power, and then supplied via the directional couplers 5 and 6, respectively. After measuring the power and the reflected power, respectively, they are supplied to the mode converter 7, and the square TE for the measuring thread is supplied. The mode is converted to the circular TEon mode, and only the circular TEo+ mode electromagnetic waves taken out through the mode filter 8 are supplied to the test mode converter 10 having the configuration shown in FIG. 4 through the Taber tube 9 for pipe diameter conversion. . The detector 11 detects the far-field radiated electric field from the end face opening of the test mode converter 10, and the radiation pattern is analyzed to calculate the power of each propagation mode TEo+, TEoz, and TEos.

On the other hand, in FIGS. 7 to 9 showing the above-mentioned measurement results, the solid line indicates the theoretical value, and the dotted line indicates the measured value. Further, the first point in each figure indicates each power ratio in the input, and the last point indicates each power ratio finally obtained as shown in Table 2.

(Effects of the Invention) As is clear from the above explanation, according to the present invention, the circular waveguide Tε, which is often used for direct heating of nuclear fusion plasma, etc.
. , -TH,,For the mode converter, instead of the conventional sinusoidal periodic structure that requires a considerable amount of precision manufacturing technology and a huge amount of calculation for optimization, we have created an extremely simple step-like periodic structure. By using it, the following remarkable effects can be achieved.

(1) The periodic structure is extremely simple compared to the conventional sinusoidal periodic structure, and manufacturing is much easier.

(2) By using an oversized circular waveguide as a mode changer, an exact solution can be obtained with a much smaller amount of calculation than with the conventional sinusoidal periodic structure, which requires an enormous amount of calculation to obtain only an approximate solution. Optimum design can be easily carried out, and the degree of freedom is large.

(3) Since the discontinuous deviation due to the periodic structure from the average radius of the circular waveguide can be prevented from becoming too large, it can withstand a certain amount of high power.

[Brief explanation of the drawing]

FIG. 1 is a vertical cross-sectional view schematically showing an example of the configuration of a circular waveguide mode converter with a stepped periodic structure according to the present invention, and FIG. 2 is a schematic diagram showing the configuration of a conventional circular waveguide mode converter with a sine wave periodic structure. 3 is a drawing defining the initial values of the design of the mode converter of the present invention; FIG. 4 is a longitudinal sectional view showing a specific example of the design values of the mode converter of the present invention; FIG. 5 are the same (longitudinal cross-sectional view showing other specific examples of the design values; FIG. 6 is a configuration layout diagram showing the schematic configuration of the power conversion efficiency measurement system based on the far-field radiated electric field of the mode converter of the present invention; FIGS. 7 to 7). FIG. 9 is a characteristic curve diagram showing the measurement results of the power conversion efficiency for each propagation mode. 1... Gunn oscillator 2... Circulator for absorbing reflected power 3... Frequency meter 4... Variable attenuator 5.6... Directional coupler for power measurement 7... Rectangular-circular mode converter 8... Mode filter 9... Taber tube 10...
・Test mode converter 11...Detector Figure 1 Figure 2 Figure 3

Claims (1)

[Claims] 1. At least once at a predetermined period over a predetermined range of pipe diameter
It consists of a circular waveguide with a discontinuous part that increases and decreases repeatedly in steps, and the TE_o_n mode - TE_o_m
A circular waveguide mode converter with a stepped periodic structure, characterized in that it converts electromagnetic wave transmission modes between modes. 2. The circular waveguide mode converter according to claim 1, wherein the at least one stepwise repeated increase/decrease is a rectangular wave-like increase/decrease. 3. The predetermined period is the TE_o_n mode and the T
It is set based on the heat wavelength between the E_o_m mode and the predetermined range of increase/decrease in the tube diameter, which represents the number of repetition periods of increase/decrease in the tube diameter, each phase constant of the TE_o_n mode and the TE_o_m mode, and electromagnetic wave transmission. The stepped periodic structure circular waveguide mode converter according to claim 1 or 2, wherein the step-like periodic structure circular waveguide mode converter is set based on the n-th and m-th zero points excluding 0 of the first-order Bessel function. . 4. Claim 1 or 2, characterized in that the predetermined period and the predetermined range set as described in Claim 3 are optimized using a mode matching technique. The step-like periodic structure circular waveguide mode converter described in 2.