JP3737445B2 - Waveguide-microstrip line converter and converter parts - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a waveguide-microstrip line converter and a converter component used in a microwave band or a millimeter wave band.
[0002]
[Prior art]
A waveguide-microstrip line converter is frequently used as a component for appropriately joining a waveguide and a microstrip line included in a planar circuit with low loss.
FIG. 8 is an explanatory view of the structure of a conventional waveguide-microstrip line converter of this type. In this figure, for convenience of explanation, the thickness of the waveguide and the outer wall shape are omitted.
In the waveguide-microstrip line converter shown in FIG. 8, the microstrip line 31 is parallel to the electric field of the steady distribution of the rectangular waveguide 20 whose inner wall long side is A and whose inner wall short is B. The dielectric substrate 30 on which is formed is arranged. The inner end face of the rectangular waveguide 20 is a short-circuit face that is parallel to the microstrip line 31. The end portion having this short-circuit surface is usually called a “waveguide back short”. In the following description, this end portion is referred to as a waveguide back short 5.
The tip end portion (waveguide side) of the microstrip line 31 is open and becomes an open end portion 32. The transmission fundamental mode of the rectangular waveguide 20 is a TE10 mode, and the transmission fundamental mode of the microstrip line 31 is a quasi-TEM mode.
[0003]
FIG. 9 is a cross-sectional view showing the electric field distribution in the conversion mechanism of such a waveguide-microstrip line converter. In FIG. 9, the thickness and part of the outer wall shape of the rectangular waveguide 20 and the waveguide back short 5 are drawn to explain the hole 1 d and the like for passing the microstrip line 31. As shown in FIG. 9, in the conversion mechanism, the electric field distribution e1 of the TE10 mode of the rectangular waveguide 20 and the electric field distribution e2 of the quasi-TEM mode of the microstrip line 31 are the inside of the rectangular waveguide 20 and the waveguide. In the cavity (inner space) of the tube back short 5, conversion is performed while being disturbed with each other.
[0004]
FIG. 10 is an equivalent circuit of a waveguide-microstrip line converter, in which the characteristic impedance of the TE10 mode transmission line 20 ′ in the rectangular waveguide 20 is Z1, and the microstrip is branched and joined (point aa ′). The characteristic impedance of the quasi-TEM mode transmission line 31 ′ in the line 31 is Z2.
In the waveguide-microstrip line converter, the characteristic impedances Z1 and Z2 need to be properly matched. Therefore, the dimension of the waveguide back short 5 (length from the microstrip line 31 to the short-circuit point 50 ′ (the short-circuit surface 50 of the waveguide back short 5 in FIG. 9): hereinafter referred to as “short circuit line length”. L) and the dimension of the open end 32 of the microstrip line 31 are selected to be eigenvalues corresponding to the size of the rectangular waveguide 20, the thickness / relative permittivity of the dielectric substrate 30, and the operating frequency.
[0005]
As shown in FIG. 11, the dielectric substrate 30 has the same end portion dimension as the inner wall long side dimension A of the rectangular waveguide 20, and the length of the portion in contact with the cavity of the waveguide back short 5. The length (the length in the downward direction from the portion indicated by the broken line in FIG. 11) is the same as the dimension B of the short side of the inner wall of the rectangular waveguide 20. The line width W1 of the microstrip line 31 is uniquely determined according to the set characteristic impedance. The open end 32 has a width W2 that is slightly wider than the line width W1 of the microstrip line 31 and a size that enters the inside of the waveguide from the long side surface of the rectangular waveguide 20 by a length T. The width W2 and the length T of the open end 32 are uniquely determined according to the size of the inner wall of the rectangular waveguide 20, the material of the dielectric substrate 30, etc. mainly for the purpose of impedance matching.
[0006]
FIG. 12 is a schematic view of the waveguide back short 5.
The waveguide back short 5 has an inner end face parallel to the electric field in the steady distribution when joined to the rectangular waveguide 20 as a short-circuited surface 50, a pair of inner side surfaces as an E plane, and an upper long side surface. A notch 53 as shown is formed in a part. In order to facilitate the joining with the rectangular waveguide 20, the flange 51 in which a plurality of holes 52 are formed may be integrally formed with the back short outer wall. In use, the dielectric substrate 30 is bonded to the rectangular waveguide 20. Joining is performed by inserting a dedicated screw into the hole 52 of the flange 51 after positioning with the rectangular waveguide 20.
The size of the opening of the waveguide back short 5 is the same as the opening of the rectangular waveguide 20. That is, the dimension of the long side of the inner wall is A, and the dimension of the short side of the inner wall is B.
[0007]
The reflection characteristics of the conventional waveguide-microstrip line converter configured as described above are as shown in FIG. Originally, the reflected wave generated due to the conversion of the transmission fundamental mode is unnecessary. In order to avoid the adverse effect of the reflected wave in the required band, the return loss of −20 dB or less should be realized. Yes.
Regarding the structure and operation of the waveguide-microstrip line converter as described above, reference can be made to the descriptions in JP-A-60-230701 and US Pat. No. 5,202,648.
[0008]
[Problems to be solved by the invention]
The above-described conventional waveguide-microstrip line converter has the following problems to be solved.
The first problem is that impedance matching is difficult within a desired band.
In the equivalent circuit of FIG. 10, the basic required performance as a waveguide-microstrip line converter is that the characteristic impedance Z1 of the TE10 mode transmission line 20 ′ and the characteristic impedance Z2 of the quasi-TEM mode transmission line 31 ′ are not. There is no consistency. Normally, the characteristic impedance Z1 at the operating frequency is 300 ohms to 500 ohms (defined by voltage and current), and the characteristic impedance Z2 is selected to be 50 ohms. It is not easy to match characteristic impedances with such a large difference, but in the waveguide-microstrip line converter, the electromagnetic field distribution itself is quite different, which makes impedance matching difficult. It has become a factor.
[0009]
At the time of manufacture, the short circuit circuit line length L of the waveguide back short 5 and the width W2 and length T of the open end 32 are selected and processed to optimum values obtained by calculation in advance. In some cases, the above optimum value deviates from the calculated value, resulting in deterioration of reflection characteristics. If this degradation of reflection characteristics becomes a value that cannot be ignored, it will lead to degradation of the performance of the waveguide-microstrip line converter or the entire device equipped with it, so measures to add "broadband matching" or "matching adjustment function" Is required.
[0010]
The second problem is that the waveguide back short 5 cannot be miniaturized.
Since the size of the rectangular waveguide 20 increases as the operating frequency decreases, the physical size of the waveguide back short 5 also increases accordingly. In the equivalent circuit of FIG. 10, the short-circuit line length L needs to be a length that becomes “open” when the short-circuit side is viewed from the point aa ′, and therefore 1 / of the in-tube wavelength of the rectangular waveguide 20. It is selected around 4 wavelengths. Therefore, when manufacturing a waveguide-microstrip line converter used in a frequency band of 10 GHz or less in the microwave band, the size of the waveguide back short 5 becomes a bottleneck.
[0011]
The present invention solves these problems, and an improved waveguide-microstrip line converter and converter capable of electrically adjusting the characteristics of a conversion mechanism determined according to a physical structure, such as reflection characteristics, etc. Providing parts is an issue.
[0012]
[Means for Solving the Problems]
The present invention is a waveguide-microstrip capable of, for example, increasing / decreasing the guide wavelength equivalently while maintaining the conversion performance of the transmission fundamental mode, and thereby adjusting the characteristics of the conversion mechanism afterwards. A line converter is provided.
The waveguide-microstrip line converter includes a conversion mechanism for converting a transmission fundamental mode between the waveguide and a microstrip line arranged in parallel with the electric field of steady distribution in the waveguide, In the waveguide-microstrip line converter in which the characteristics of the conversion mechanism are determined according to the physical structure of the predetermined portion of the waveguide, a metal member that electrically changes the conversion characteristics is provided at the predetermined portion. It has been deployed. The “characteristic” here is, for example, the above-described reflection characteristic, impedance characteristic, or other electrical characteristic. The “physical structure” is, for example, the above-mentioned inner wall long side, inner wall short side, and short circuit line length.
In such a waveguide-microstrip line converter, since the electric field distribution in the waveguide is concentrated on the metal member, the characteristics can be adjusted afterwards.
[0013]
The transmission fundamental mode of the waveguide is a TE10 mode, the transmission fundamental mode of the microstrip line is a quasi-TEM mode, and the predetermined portion is a short-circuited surface parallel to a steady-distributed electric field in the waveguide. And the metal member is disposed in a direction perpendicular to each of the short-circuit plane and each of the two E planes. . A configuration in which the metal member is provided only on the short-circuit surface or only on one of the two E surfaces is also possible. In any case, it is desirable that the size protruding from each surface into the waveguide is adjustable.
The metal member has a predetermined shape supported by the outer wall of the waveguide end so that the insertion length into the waveguide can be adjusted. It may be a screw provided with a screwing mechanism.
[0014]
The waveguide end may be a resin molded product obtained by metallizing a part or all of the surface thereof, and a part of the metal member is fixed to the resin molded product. May be. In this way, mass production becomes easy and a significant cost reduction is possible.
[0015]
Another waveguide-microstrip line converter of the present invention is provided between a TE10 mode waveguide and a quasi-TEM mode microstrip line placed in parallel with a stationary electric field in the waveguide. A waveguide having a conversion mechanism for converting a transmission fundamental mode, and the characteristics of the conversion mechanism are determined according to the physical structure of the end of the waveguide in which a cavity in contact with the microstrip line is formed. In the microstrip line converter, a dielectric that changes the conversion characteristics in accordance with the shape and relative permittivity of the cavity is replaceably provided.
The entire space of the cavity may be filled with a dielectric that changes the conversion characteristics according to its shape and relative dielectric constant. In this way, it is possible to reduce the size of the converter while allowing adjustment of required characteristics.
The waveguide end back short can be formed of a resin molded product obtained by metallizing part or all of its surface.
[0016]
The converter component of the present invention is a waveguide that converts a transmission fundamental mode between a TE10 mode waveguide and a quasi-TEM mode microstrip line arranged in parallel with the electric field of steady distribution in the waveguide. A converter part used in a tube-microstrip line converter, having a short-circuited surface parallel to a steady-distributed electric field in the waveguide on its inner end surface, and two E-planes on its inner surface Each of the short-circuit plane and the two E planes is provided with a metal member in a direction perpendicular to the plane, and the metal member can be adjusted in size to protrude into the waveguide. Therefore, the conversion characteristics are electrically changed according to the protruding size.
A part or all of the surface of the converter part may be molded with a resin subjected to metallization, and a part of the metal member may be fixed to the resin.
[0017]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
<First Embodiment>
FIG. 1 is an explanatory view of the structure of a waveguide-microstrip line converter according to a first embodiment of the present invention. For convenience, the same components as those of the conventional one shown in FIG. 1 is the same as FIG. 8 in that the thickness, outer wall shape, and the like of the rectangular waveguide 20 are omitted. In addition, the dielectric substrate 30 having the microstrip line 31 formed in parallel with the electric field of the steady distribution of the rectangular waveguide 20 is disposed, and the open end 32 is formed at the tip of the microstrip line 31. Is the same as that shown in FIG. The transmission fundamental mode of the rectangular waveguide 20 is a TE10 mode, and the transmission fundamental mode of the microstrip line 31 is a quasi-TEM mode.
[0018]
The waveguide-microstrip line converter of this embodiment is different from the waveguide back short 5 shown in FIG. 8 in the structure of the waveguide back short (however, the point made of a conductive member is the same).
The waveguide back short 1 of this embodiment has a structure in which the short circuit line length L is increased or decreased equivalently, thereby matching the impedance at the time of mode conversion. Specifically, metal posts 10, 11, and 12, which are examples of metal members, are inserted in a direction perpendicular to each surface into each of the short-circuit surface 1 a and the two E surfaces 1 b and 1 c of the waveguide back short 1, In addition, the insertion length of each metal post 10, 11, 12 into the waveguide back short 1, that is, the protrusion size from the short-circuited surface is made variable, thereby realizing an adjustment mechanism for subsequent impedance matching. ing. The deployment positions of the metal posts 10, 11, and 12 on each of the surfaces 1a1b and 1c may be arbitrary, but are preferably near the center.
The metal posts 10, 11, and 12 may be supported by the outer wall hole, or may be supported by a reciprocating support mechanism attached to the outer wall surface. The metal post itself may expand and contract. Further, in place of the metal posts 10, 11, 12, screw-in type metal screws (metal screws) can be used.
[0019]
When the metal post 10 is inserted into the short-circuit surface 1a of the waveguide back short 1, the electric field distribution is concentrated on the metal post 10, so that the short-circuit line length L can be made equivalently variable. In the case of the metal posts 11 and 12 arranged perpendicularly to the E faces 1b and 1c, the inner wall long side dimension A is equivalently shortened, and the in-tube wavelength in the TE10 mode in the waveguide back short 1 is increased. can do. That is, even if the short-circuit line length L is constant, the short-circuit line electrical angle Φ decreases as the in-tube wavelength increases.
[0020]
The relationship between the dimension A of the inner wall long side of the TE10 mode and the guide wavelength λgo is expressed by the following equation.
λgo = λo / √X
X = 1− (λo / (2A)) ² (1)
Where λo is a free space wavelength. Further, the short-circuit line electrical angle Φ is expressed by the following equation.
Φ = 2πL / λgo (2)
[0021]
Since the metal posts 10, 11, and 12 act independently with respect to the electric field, it is not necessary to use three at the same time as shown in the figure, and only one or two may be used. Further, the number of metal posts 10, 11, and 12 may be arbitrarily determined depending on the performance required for the waveguide-microstrip line converter and the processing accuracy of the waveguide back short 1.
[0022]
FIG. 2 is a diagram showing the electric field distribution of the conversion unit in the waveguide-microstrip line converter according to this embodiment. In both the TE10 mode in the rectangular waveguide 20 and the quasi-TEM mode in the microstrip line, the direction of the electric field is actually inverted every half wavelength. However, in FIG. The distribution of is shown. Moreover, only the metal post provided on the short-circuit surface is illustrated. In the case of the example shown in FIG. 2, the electric field distribution is concentrated on the metal post 10, and if the insertion length S is increased, the short-circuit line length L is equivalently shortened, and conversely if the insertion length S is shortened. Equivalently, the short-circuit line length L becomes longer. Thus, even if the short circuit line length L is constant, the electrical angle of the short circuit line decreases as the in-tube wavelength becomes longer. By making the insertion amount S of the metal post 10 variable, the short-circuit line length L can be arbitrarily adjusted.
As the insertion length of the metal posts 11 and 12 is increased, the inner wall long side dimension A is equivalently shortened, so that the TE10 mode waveguide wavelength transmitted in the waveguide back short can be increased.
[0023]
As an example of the characteristics of the waveguide-microstrip line converter that changes according to this embodiment, the reflection characteristics in the 17 GHz band are shown in FIG. It can be seen that the reflection characteristics of the conventional waveguide-microstrip line converter shown in FIG. 13 are improved.
[0024]
Second Embodiment
The structure of the waveguide-microstrip line converter according to the second embodiment of the present invention is shown in FIG. For convenience, the same components as those of the conventional one shown in FIG. 3 is the same as FIGS. 1 and 8 in that the thickness, outer wall shape, and the like of the rectangular waveguide 20 are omitted. Further, the dielectric substrate 30 on which the microstrip line 31 is formed is arranged in parallel with the electric field of the steady distribution of the rectangular waveguide 20, and an open end 32 is formed at the tip of the microstrip line 31. The point is also the same as that shown in FIGS. Since the rectangular waveguide 20 is used, the basic transmission mode is the TE10 mode, and the basic transmission mode of the microstrip line 31 is the quasi-TEM mode.
[0025]
In this embodiment, a dielectric 13 is replaceably disposed in a cavity in the waveguide back short 2. As a material of the dielectric 13, for example, Teflon (registered trademark) having a relative dielectric constant εr of about 2 can be used.
The TE10 mode in-tube wavelength λg when the dielectric 13 is present in the cavity can be expressed by the following equation.
λg = λgo / √ (η · εr) (3)
Where η is the dielectric filling factor (ratio of the dielectric occupying the entire space of the cavity), εr is the relative dielectric constant of the dielectric, and λgo is the in-tube wavelength when εr is “1”.
[0026]
By making the dielectric filling factor η and the relative dielectric constant εr variable, the guide wavelength λgo can be changed, and the characteristics of the conversion mechanism in the waveguide-microstrip line converter, for example, the short-circuit line described above The electrical angle Φ can be adjusted afterwards. The dielectric filling factor η is determined by the size of the dielectric, and the relative dielectric constant εr is determined by the type of the dielectric.
[0027]
The shape of the dielectric 13 can be freely selected, and depending on the shape and the value of the relative permittivity εr, the reflected wave itself from the dielectric itself may contribute to impedance matching. Range that can be adjusted automatically.
[0028]
In FIG. 3, Teflon (registered trademark) processed in a step shape is used as the dielectric 13, but this is sufficiently large when the size of the waveguide-microstrip line converter is about the millimeter wave band. This is because improvement in impedance characteristics, that is, impedance matching, is more important than size reduction. By processing in a step-like manner and changing the position of the dielectric 13, the subsequent adjustment of impedance characteristics becomes easy. That is, the impedance value can be changed stepwise by changing the position and shape of the step, and the value can be finely adjusted by changing the position of the dielectric 13.
[0029]
FIG. 4 is a diagram illustrating an electric field distribution of a conversion unit in the waveguide-microstrip line converter according to the second embodiment. As is apparent from FIG. 4, the electric field distribution changes according to the shape of the dielectric 13. Therefore, fine adjustment can be performed by making short circuit line length L1, L2, L3 variable.
The dielectric 13 includes a step-shaped dielectric 13 as shown in FIG. 5A, a tapered dielectric 14 as shown in FIG. 5B, and a planar dielectric as shown in FIG. 5C. 15 can also be used. In the tapered dielectric 14, the impedance changes in a tapered shape, so that the impedance characteristics can be easily adjusted.
[0030]
<Third Embodiment>
FIG. 6 is a schematic view of a waveguide back short in the waveguide-microstrip line converter according to the third embodiment.
The illustrated waveguide back short 3 is obtained by replacing the waveguide back short made of a conductive member described in the first embodiment with a plastic molded product. At that time, in order to make the electromagnetic field boundary condition equivalent to the metal processed product (waveguide back short 1 of the first embodiment), the outer surface and the inner surface of the plastic molded product are metalized. Reference numerals 40, 41, and 42 are metallized posts that have been metallized and fixed in position.
[0031]
The technology of metallizing on the surface of plastic is common, but the film thickness at the time of metallization sufficient to guarantee the predetermined transmission characteristics in the microwave band and the millimeter wave band should naturally be highly accurate. Required.
According to the experiments by the present inventors, by setting the film thickness to 5 times or more the skin dips value that can be uniquely calculated by the type of metal used for the metallization process and the transmission frequency, it is almost the same as the case of the conductive member. It has been found that the characteristic waveguide backshort 3 results.
[0032]
FIG. 7 shows a case where the metallized posts 40, 41, and 42 shown in FIG. 6 have unstable electrical characteristics and the insertion length in the cavity direction needs to be variable. Is replaced with metal screws 43, 44, and 45 so that can be changed.
[0033]
<Fourth embodiment>
In the second embodiment, the example in which the dielectric 13 is replaceably disposed in the cavity has been described. However, the dielectric may be filled not only in a part of the waveguide back short, but also in the whole. Good. For example, the second problem can be easily solved by filling a dielectric having a relative dielectric constant of 4.0 with a filling rate of 100%.
[0034]
Taking the case of configuring a conventional waveguide-microstrip line converter in the 10 GHz band as an example, the degree of improvement is clear.
That is, the rectangular waveguide 20 is WR90 (EIA standard), the inner wall long side dimension A is 22.86 mm, and the inner wall short side dimension B is 10.16 mm. Characteristic impedance at 10 GHz (defined by voltage and current) Z1 is 348 ohms. When this is mode-converted to the microstrip line 31 having a characteristic impedance Z2 of 50 ohms, 10 mm is required if the short circuit line length L of the waveguide back short is selected to be ¼ wavelength (in-tube wavelength). However, when the dielectric in the waveguide back short is filled with a dielectric having a relative dielectric constant of 4.0 with a filling rate of 100%, the short circuit line length L of the waveguide back short can be shortened to 5 mm. This means that the in-tube wavelength of the waveguide is shortened by filling the dielectric. The relationship between the dielectric constant of the dielectric to be filled and the wavelength in the tube is the same as the above equation (3).
[0035]
【The invention's effect】
As described above, according to the present invention, it is possible to improve characteristic failures (impedance mismatch etc.) afterwards due to physical structural changes or defects such as variations in processing of the waveguide end portions. A unique effect is obtained.
[Brief description of the drawings]
FIG. 1 is an overview of a waveguide-microstrip line converter according to a first embodiment of the present invention.
FIG. 2 is an explanatory diagram of an electric field distribution of a conversion part of the waveguide-microstrip line converter according to the first embodiment.
FIG. 3 is a schematic view of a waveguide-microstrip line converter according to a second embodiment of the present invention.
FIG. 4 is an explanatory diagram of an electric field distribution of a conversion part of a waveguide-microstrip line converter according to a second embodiment.
5A and 5B are diagrams showing the shape of a dielectric, in which FIG. 5A shows an example of a step-like dielectric, FIG. 5B shows an example of a tapered dielectric, and FIG. 5C shows an example of a linear dielectric.
FIG. 6 is an explanatory view of a waveguide back short whose surface is metallized.
FIG. 7 is an explanatory view of a waveguide back short in which the surface and the surface of a molded metal post are metallized.
FIG. 8 is a schematic view of a conventional waveguide-microstrip line converter.
FIG. 9 is an explanatory view of a conversion portion electric field distribution of a conventional waveguide-microstrip line converter.
FIG. 10 is an equivalent circuit of a waveguide-microstrip line converter.
FIG. 11 is a structural explanatory diagram of a dielectric substrate on which a microstrip line is formed.
FIG. 12 is a schematic view of a conventional waveguide back short.
FIG. 13 is a reflection characteristic diagram of a conventional waveguide-microstrip line converter.
FIG. 14 is a reflection characteristic diagram of the waveguide-microstrip line converter according to the first embodiment.
[Explanation of symbols]
1, 2, 3, 5 Waveguide back short 1a, 50 Short circuit surface 1b, 1c E surface 1d Hole for passing microstrip line
10,11,12, metal post (screw screw, screw)
40,41,42,43,44,45 Metallized post (screw, screw)
13, 14, 15 Dielectric 20 Rectangular waveguide 30 Dielectric plate 31 Microstrip line 32 Open end 51 Flange 52 Screw hole 53 Notch

Claims (2)

Comprising TE10 mode and waveguide, a conversion mechanism for converting a transmission fundamental mode between the microstrip line of the quasi-TEM mode disposed in parallel to the electric field of the TE10 mode in the waveguide,
In the microstrip line converter, - properties of the conversion mechanism, inside the microstrip line in contact with the waveguide which is determined depending on the physical structure of the waveguide end cavity is formed
It said cavity, characterized by being deployed freely exchanged change is causing dielectric the conversion characteristics in accordance with the shape and dielectric constant,
Waveguide-microstrip line converter. The waveguide end is a resin molded product obtained by metallizing a part or all of the surface thereof ,
The waveguide-microstrip line converter according to claim 1.

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