JP2016111459A - Millimeter wave band transmission path conversion structure - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a millimeter wave band transmission path conversion structure which can be easily manufactured, can be reduced in a size, and hardly causes characteristics variation in a wide band.SOLUTION: A millimeter wave band transmission path conversion structure connecting between a microstrip line 10 in which a main conductor 12 is formed to one surface side of a dielectric substrate 11 and a ground conductor 13 is formed in an opposite surface side and a wave guide pipe 20, has a wave guide pipe structure formed so that a wave guide path 31 having a predetermined aperture and a predetermined length is surrounded by a metal wall 32. By forming so as to be continuously provided dielectric layers 133 and 134 of a plural number M (M=2) having a different relative dielectric constant from one end to the other end of the wave guide path 31, connecting one end surface of the wave guide path 31 to an end surface of one end side of the dielectric substrate 11 of the microstrip line 10, and connecting the other end surface of wave guide path 31 to one end side opening surface of the wave guide pipe 20, a gap of the microstrip line 10 and the wave guide pipe 20 is connected in a matching state in a frequency range having a wide milli-wave zone.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a transmission line conversion structure for efficiently transmitting a millimeter-wave band signal between a microstrip line and a waveguide over a wide band.

  In a measuring instrument that measures a signal having a high frequency such as a millimeter wave band, a waveguide with a small loss in the millimeter wave band is often used as an input / output transmission line. Circuit), it is necessary to connect between the strip line (microstrip line or coplanar line) formed on the printed circuit board on which the IC to be tested is mounted and the waveguide on the measuring instrument side. While the impedance of the strip line is generally about 50 to 100Ω, the impedance of the waveguide reaches several hundreds of Ω, so it is not easy to take impedance matching.

  As a technique for solving this, a method of bringing a coupling ridge portion of a ridge waveguide into contact with a microstrip line as in Patent Document 1, or a microstrip line from a side surface of a waveguide as in Patent Document 2 A method of inserting vertically is known.

JP-A-5-83014 JP 2008-79085 A

  However, the method of Patent Document 1 has a problem that when the frequency becomes high, the ridge portion becomes thin and the manufacture becomes difficult, and the accuracy required for contact with the microstrip line increases, and the difficulty of assembly increases. .

  Further, when the IC to be measured has many signal terminals, these strip lines are necessarily provided radially on the mount substrate. However, in the method of Patent Document 2, the tip of the strip line is connected to the waveguide. Therefore, many waveguides must be arranged from the end of each strip line so as to be orthogonal to the end of each strip line, which makes it very difficult to manufacture. Further, if a bend is provided in the middle portion of the waveguide in order to avoid this, there is a problem that the entire system becomes large. Further, it is known that there is a problem that the characteristics vary depending on the position of the strip line inside the waveguide.

  An object of the present invention is to provide a millimeter-wave band transmission line conversion structure that solves these problems, is easy to manufacture, can be configured in a small size, and does not easily vary in characteristics over a wide band.

In order to achieve the above object, a millimeter-wave band transmission line conversion structure according to claim 1 of the present invention provides:
It consists of a main conductor (12) formed on one side of the dielectric substrate (11) and an earth conductor (13) formed on the opposite side, and propagates an electromagnetic wave in the millimeter wave band in the length direction of the main conductor. In the millimeter waveband transmission line conversion structure for connecting the microstrip line (10) and the waveguide (20) capable of propagating millimeter wave electromagnetic waves,
A plurality of M dielectric layers (133, 134) having a waveguide structure in which a waveguide (31) having a predetermined diameter and a predetermined length is surrounded by a metal wall (32) and having different relative dielectric constants The microstrip line is formed so as to be continuous from one end to the other end of the waveguide, and one end face of the waveguide is joined to the end face of the dielectric substrate on one end side of the main conductor of the microstrip line. Propagating the electromagnetic wave in the millimeter wave band with one end side of the waveguide, and joining the other end face of the waveguide to the one end side opening face of the waveguide, The electromagnetic wave of the millimeter wave band is formed to propagate between one end side of the waveguide.

The millimeter waveband transmission line conversion structure according to claim 2 of the present invention is the millimeter waveband transmission line conversion structure according to claim 1,
Desired propagation frequency _{f 1,} f 2 of a plurality N (≧ M) having different within the frequency band, ...... _f the combined impedance of the waveguide for electromagnetic waves _{N Z x1, Z x2, ......} Z xN, the waveguide _Are the impedances Z _w1 , Z _w2 ,... Z _wN and the impedance Z1 of the microstrip line,
Z _x1 = √ (Z1 × Z _w1 )
Z _x2 = √ (Z1 × Z _w2 )
......
Z _xN = √ (Z1 × Z _wN )
And the M frequencies of the plurality N of frequencies f ₁ , f ₂ ,... F _N are denoted by f _{a1 to} f _aM ,
An in-tube wavelength when an electromagnetic wave having a first frequency f _a1 propagates through the first dielectric layer of the plurality of dielectric layers is λ _g1 ,
An in-tube wavelength when an electromagnetic wave having a second frequency f _a2 propagates through the second dielectric layer of the plurality of dielectric layers is λ _g2 ,
......
An in-tube wavelength when an electromagnetic wave having an Mth frequency _faM propagates through the Mth dielectric layer of the plurality of dielectric layers is λ _gM.
When the length L of the waveguide is
L = λ _g1 / 4 = λ _{g2 /4=...=λ gM} / 4
Thus, the diameter of the waveguide and the relative dielectric constant of each dielectric layer are set.

Further, the millimeter waveband transmission line conversion structure according to claim 3 of the present invention is the millimeter waveband transmission line conversion structure according to claim 1 or 2,
The plurality M is 2, the first dielectric layer is made of a dielectric having a relative dielectric constant greater than 1, and the second dielectric layer is an air layer having a relative dielectric constant of 1. And

Moreover, the millimeter wave band transmission line conversion structure of Claim 4 of this invention is a millimeter wave band transmission line conversion structure in any one of Claims 1-3,
One end side of the main conductor of the microstrip line is surrounded by a metal wall (35a to 35c) for a predetermined length, and from a boundary part between the microstrip line and the waveguide in which the plurality of dielectric layers are formed. A radiation wave guide (35) forming a radiation wave guide path (36) for guiding the radiation wave radiated to the external space to the other end of the main conductor;
A groove (37) having a depth corresponding to ¼ of the wavelength of the desired propagation frequency is provided on the inner periphery of the metal wall of the radiation wave guide for preventing leakage of the radiation wave.

Further, the millimeter waveband transmission line conversion structure according to claim 5 of the present invention is the millimeter waveband transmission line conversion structure according to any one of claims 1 to 4,
Metal posts (45) for connecting a part of the metal wall surrounding the waveguide to the ground conductors (41, 42, 43) provided on both surfaces of the dielectric substrate (40) by through-hole processing at a predetermined interval. It is characterized by being formed side by side.

The millimeter waveband transmission line conversion structure according to claim 6 of the present invention is the millimeter waveband transmission line conversion structure according to any one of claims 1 to 5,
One of the plurality of dielectric layers is formed by extending a dielectric substrate of the microstrip line.

Further, the millimeter waveband transmission line conversion structure according to claim 7 of the present invention is the millimeter waveband transmission line conversion structure according to any one of claims 1 to 6,
The diameter of one end of the waveguide is set to a size corresponding to the diameter of the waveguide in which the plurality of dielectric layers are formed, and the diameter increases toward the other end. .

  With this configuration, in the millimeter waveband transmission line conversion structure according to claim 1 of the present invention, a waveguide structure having a waveguide in which a plurality of dielectric layers having different relative dielectric constants are continuously formed from one end to the other end. Because it is a structure that propagates electromagnetic waves in the millimeter wave band between the one end side and the microstrip line and between the other end side and the waveguide, the microstrip line and the waveguide are in a straight line. Can be connected to each other, can be easily manufactured, can be configured in a small size, and variations in characteristics are less likely to occur.

Further, as in claim 2, for a plurality of N different frequencies in the desired propagation frequency band, the combined impedance Z _{xi of the} waveguide composed of a plurality of dielectric layers is the impedance Z1 of the microstrip line and the impedance Z of the waveguide. Z _xi = √ (Z1 × Z _wi ) (i = 1 to N) with respect to _wi , and ¼ of the waveguide wavelength when propagating through each dielectric layer for M frequencies is the length of the waveguide The diameter of the waveguide and the relative dielectric constant of the dielectric layer are set so that they are equal to each other, so that the waveguide can be efficiently propagated between various microstrip lines and the waveguide in a matched state in a wide band. It has high versatility and wide bandwidth.

  Further, as in claim 3 of the present invention, the number M of dielectric layers is set to 2, a dielectric having a relative dielectric constant greater than 1 is used as the first dielectric layer, and the relative dielectric is used as the second dielectric layer. A device using an air layer with a rate of 1 can be configured in the simplest manner, and broadband matching is possible by selecting two different frequencies.

  In addition, as in claim 4 of the present invention, one end side of the main conductor is surrounded by a metal wall over a predetermined length, and radiation from the boundary between the microstrip line and the waveguide in which the dielectric layer is formed is emitted to the external space. A radiated wave guide for forming a radiated wave guide path for guiding the radiated wave to the other end of the main conductor, and an inner periphery of the metal wall of the radiated wave guide with the desired propagation frequency for preventing leakage of the radiated wave Since a groove having a depth corresponding to ¼ of the wavelength is provided, leakage of electromagnetic waves radiated from the boundary between the microstrip line and the waveguide in which the dielectric layer is formed to the external space can be prevented. it can.

  According to another aspect of the present invention, there is provided a metal post for connecting a part of the metal wall surrounding the waveguide in which the dielectric layer is formed between the ground conductors provided on both surfaces of the dielectric substrate by through-hole processing. If they are formed side by side at a predetermined interval, a waveguide can be easily formed with a narrow width, and manufacturing is further facilitated.

  Further, if one of the plurality of dielectric layers has a structure in which the dielectric substrate of the microstrip line is extended and used, the conversion structure is integrally formed on one end side of the microstrip line. And the structure can be further simplified.

  Further, as described in claim 7, the diameter of one end side of the waveguide is set to a size corresponding to the diameter of the other end side of the waveguide in which the dielectric layer is formed, toward the other end side. Since the aperture is formed to be large, reflection between the waveguide in which the dielectric layer is formed and the waveguide can be suppressed, and the waveguide having a diameter that is typically used in the millimeter wave band The connection becomes easier.

The figure which shows the conversion structure used as the premise of this invention The figure which shows the basic structure of this invention Diagram showing a structure with reduced radiation The figure which shows the simulation result of the structure of FIG. The figure which shows the simulation result when the microstrip line is shifted in the X direction with the structure of FIG. The figure which shows the simulation result when a microstrip line is shifted to a Z direction with the structure of FIG. The figure which shows the example which formed the metal wall surrounding a waveguide with a metal post The figure which shows the structure using the waveguide of FIG. Diagram showing an example of a structure in which one of the dielectric layers is formed by extending a dielectric substrate of a microstrip line The figure which shows another structural example in which one of the dielectric layers is formed by extending a dielectric substrate of a microstrip line

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. First, a prerequisite technology of the millimeter waveband transmission line conversion structure of the present invention will be described.

  FIG. 1 is a diagram showing a basic structure as a prerequisite technology. FIG. 1A shows a microstrip line 10 and a waveguide 20 that can transmit electromagnetic waves in a millimeter wave band (for example, 60 to 90 GHz). FIG. 1B is an exploded view showing the transmission path converter 30 as a separate body, and FIG. 1B is a side sectional view showing a connection state.

In the microstrip line 10, a strip-shaped main conductor 12 is patterned from one end to the other end on one surface side of the dielectric substrate 11, and the opposite surface side is covered with a ground conductor 13. The impedance of the transmission line is determined by ε _r ′, the thickness t, the width of the main conductor 12, and the like. This impedance is about 50 to 100Ω that is generally used in high-frequency circuits. Examples of the dielectric substrate having a small loss in the millimeter wave band include Ro4003C (registered trademark) having a relative dielectric constant ε _r ′ = 3.55 and a thickness t = 0.3 mm.

  The waveguide 20 is a rectangular waveguide having a diameter determined by a standard in consideration of versatility, and is a WR-12 (diameter of about 3.1 × 1. 55 mm), and the impedance of the waveguide 20 varies depending on the frequency, and is, for example, 552Ω at 75 GHz. As described above, the thickness t of the dielectric substrate 11 of the microstrip line 10 is on the order of 1/10 mm, whereas the diameter of the waveguide 20 is on the order of millimeters. However, the reflection problem will be described later.

The transmission line converter 30 for connecting the microstrip line 10 and the waveguide 20 has a waveguide structure in which a waveguide 31 having a predetermined diameter (a × bmm) is surrounded by a metal wall 32 over a predetermined length. In this base technology, the waveguide 31 is filled with a dielectric 33 having a relative dielectric constant ε _r greater than 1. Here, the height of the waveguide 31 (thickness of the dielectric 33) b is described as being equal to the thickness t of the dielectric substrate 11 of the microstrip line 10, but the thicknesses of both are different. May be.

  Then, one end face 31 a of the waveguide 31 is joined to the end face 11 a of the dielectric substrate 11 on one end side of the main conductor 12 of the microstrip line 10, and the metal walls 32 a and 32 b facing each other on one side of the waveguide 31. The end face of the upper metal wall 32a is connected to one end 12a of the main conductor 12 of the microstrip line 10, the end face of the lower metal wall 32b is connected to the ground conductor 13, and the other end face 31b of the waveguide 31 is guided. The end face of the four metal walls 32a to 32d is joined to one end side opening face 21a of the waveguide 21 of the wave tube 20, and the end face of the four metal walls 32a to 32d on the other side of the waveguide 31 is surrounded by the metal wall 22 (22a ~ 22d) are joined to one end side over the entire circumference.

  In this way, if the connection structure connects the microstrip line 10 and the waveguide 20 coaxially through the waveguide 31 filled with the dielectric 33, for example, the main conductor of the microstrip line 10 is used. 12, an electromagnetic wave in the millimeter wave band input from the other end 12 b side and propagated to the one end 12 a side is input to one end side of the waveguide 31, propagates through the waveguide 31, and enters the waveguide 20 from the other end side. Since it is output to the waveguide 21, it is easy to manufacture, can be configured in a small size, and variations in characteristics are unlikely to occur.

The length L of the waveguide 31 is ¼ of the guide wavelength λg of the electromagnetic wave having the desired propagation frequency f1, and the impedance Zx of the waveguide 31 filled with the dielectric 33 is the impedance of the microstrip line 10. The diameter a × b of the waveguide 31 and the dielectric 33 so that Zx = √ (Z1 × Z2) with respect to Z1 (which can be regarded as constant with respect to frequency) and the impedance Z2 of the waveguide 20 The relative dielectric constant ε _r is set.

  As a result, the transmission line converter 30 constitutes a quarter wavelength transformer, and the microstrip line 10 and the waveguide 20 can be connected in a matched state.

ここで、μ₀ は真空の透磁率、ε₀ は真空の透磁率、λは自由空間波長、λ_c はカットオフ周波数である。 Next, the impedance of the transmission line converter 30 having the conversion structure as the premise will be examined. If the TE wave impedance Zx ′ transmitted through the waveguide 31 of the transmission line converter 30 is vacuum,

Here, μ ₀ is the vacuum permeability, ε ₀ is the vacuum permeability, λ is the free space wavelength, and λ _c is the cutoff frequency.

となる。 On the other hand, the impedance Zx when the dielectric 31 having a relative dielectric constant ε _r is filled in the waveguide 31 is:

It becomes.

となる。 Further, considering that the cutoff frequency λ _c10 of the TE10 mode (single mode) is filled with the dielectric 33,

It becomes.

となる。 Substituting equation (3) into equation (2),

It becomes.

From the above, it can be seen that the impedance of the transmission line converter 30 can be controlled by the width a of the waveguide 31 filled with the dielectric 33 and the relative dielectric constant ε _r of the dielectric 33. Although not described in detail, the height b of the waveguide 31 (the thickness of the dielectric 33) need not be considered.

となり、導波路３１の長さＬをλ_ｇ／４に設定することで、この伝送路変換器３０を、１／４波長変成器として作用させることができる。 The guide wavelength λ _g of the transmission line converter 30 is

Thus, by setting the length L of the waveguide 31 to λ _g / 4, the transmission line converter 30 can be operated as a ¼ wavelength transformer.

In the above basic structure, a microstrip line 10 having an impedance Z1 = 100Ω using a Ro4003C (registered trademark) having a relative dielectric constant ε _r ′ = 3.55 and a thickness of 0.3 mm as a dielectric substrate 11, and a WR-12 type The transmission line converter 30 for matching the waveguide (band used 60 to 90 GHz) with a frequency of 75 GHz was calculated. However, the dielectric constant ε _r and the thickness b of the dielectric 33 are the same as those of the dielectric substrate 11 of the microstrip line 10.

  The impedance Z1 of the microstrip line 10 is 100Ω, the impedance Z2 of the waveguide 20 is 552Ω (75 GHz) from the equation (1), and the impedance Zx required for the transmission line converter 30 is Zx = √ (Z1 × Z2) 235Ω.

  The width a of the dielectric satisfying the impedance Zx = 235Ω is 2.7 mm, and ¼ of the guide wavelength λg is 1.08 mm. That is, in order to match at 75 GHz, it can be understood that the width a of the waveguide 31 (the width of the dielectric 33) is 2.7 mm and the length L is 1.08 mm.

  From this, by using the waveguide filled with the dielectric 33 as described above, transmission path conversion between the microstrip line 10 and the waveguide 20 is efficient at a desired frequency (75 GHz) and its vicinity. It can be seen that this can be done automatically.

However, when the frequency range to be transmitted is wider, it is difficult to cope with the above structure. In order to solve this, in the present invention, a plurality of M dielectric layers having different relative dielectric constants are formed in the waveguide. In addition, for a plurality of N (≧ M) different frequencies in the desired propagation frequency band, the combined impedance Z _{xi of the} waveguide composed of a plurality of dielectric layers is the impedance Z 1 of the microstrip line 10 and the impedance Z _{wi of the} waveguide 20. Z _xi = √ (Z1 × Z _wi ) (i = 1 to M), and ¼ of the in-tube wavelength when the electromagnetic wave propagates through each dielectric layer for M frequencies is the waveguide. The diameter of the waveguide 31 and the relative dielectric constant of the dielectric layer are set so as to be equal to the length. As a result, it is possible to efficiently propagate between various microstrip lines and waveguides in a state of matching in a wide band, and high versatility and wide band can be realized. Note that the dielectric layer here also includes air having a relative dielectric constant of 1 (strictly, the dielectric constant of air is larger than that of vacuum, but here the relative dielectric constant is 1).

FIG. 2 shows an example of the most simplified basic structure of M = 2. A dielectric material having a relative dielectric constant ε _r1 larger than 1 is formed inside the waveguide 31 of the transmission line converter 30 ′. The upper first dielectric layer 133 and the lower second dielectric layer 134 made of air whose relative dielectric constant ε _r2 is equal to 1 are formed so as to be continuous from one end to the other end.

  For example, the first dielectric layer 133 is made of the same material as the dielectric substrate 11 of the microsplit line 10 and has the same thickness. Further, the thickness of the second dielectric layer 134 is set to be equal to the difference between the height of the waveguide 21 of the waveguide 20 and the thickness of the first dielectric layer 133, and this structural example Then, one end side of the dielectric layer 134 is closed by the end face 13 a of the ground conductor 13 of the microstrip line 10.

となる。 In the case of this structure, from the above equation (3), the inductive wavelength λ _g1 of the electromagnetic wave propagating through the second dielectric layer 134 that is the air layer at the frequency f _{1 in} the desired frequency band has a relative dielectric constant ε _r2 of 1. Because

It becomes.

となる。 On the other hand, for another frequency f ₂ (> f ₁ ) in the desired frequency band, the in-tube wavelength λ _g2 of the electromagnetic wave propagating through the first dielectric layer 133 is

It becomes.

Therefore, 1/4 of the _guide wavelength λ _g1 when the electromagnetic wave of frequency f ₁ propagates through the second dielectric layer 134 and the guide wavelength when the electromagnetic wave of frequency f ₂ propagates through the first dielectric layer 133 The quarter of λ _g2 is made equal to the length L of the waveguide 31 (the length of the first dielectric layer 133 and the second dielectric layer 134), and the impedance of each frequency If the width a of the waveguide 31 and the dielectric constant of each dielectric layer are set so that the relationship satisfies the relationship described above, matching can be achieved in two different frequency regions, and the frequency can be reduced in a desired band. By selecting the band side and the high band side, matching can be achieved over the entire desired band, and the band can be widened.

As shown in the above structure, a specific numerical example in the case of M = 2 is shown. Four (N = 4) different frequencies are f ₁ = 60 GHz, f ₂ = 70 GHz, f ₃ = 80 GHz, and f ₄ = 90 GHz. When the impedance Z1 of the microstrip line 10 is 100Ω, the impedance Z _w1 of the waveguide 20 at the frequency f ₁ = 60 GHz = 1078Ω, and the impedance Zx = 328Ω necessary for matching with the microstrip line 10 is obtained. Here, when the width a of the waveguide 31 is 2.2 mm, the impedance is 314Ω, which substantially satisfies the matching condition. The impedance 314Ω is originally a combined impedance of the first dielectric layer 133 and the second dielectric layer 134, but the impedance of the second dielectric layer 134 made of an air layer is the first dielectric layer. Since the impedance is sufficiently larger than the impedance of the layer 133, the impedance value of the first dielectric layer 133 is used (hereinafter the same).

Further, the impedance Z _w2 of the waveguide 20 at the frequency f ₂ = 70 GHz = 721Ω, and the impedance Zx = 268Ω necessary for matching with the microstrip line 10 is obtained. As described above, when the width a of the waveguide 31 is set to 2.2 mm, the impedance is 273Ω, which substantially satisfies the matching condition.

Further, the impedance Z _w3 of the waveguide 20 at the frequency f ₃ = 80 GHz = 594Ω, and the impedance Zx = 244Ω necessary for matching with the microstrip line 10 is obtained. As described above, the impedance when the width a of the waveguide 31 is 2.2 mm is 252Ω, which substantially satisfies the matching condition.

Further, the impedance Z _w4 of the waveguide 20 at the frequency f ₄ = 90 GHz = 530Ω, and the impedance Zx = 230Ω necessary for matching with the microstrip line 10 is obtained. As described above, when the width a of the waveguide 31 is set to 2.2 mm, the impedance is 238Ω, which substantially satisfies the matching condition.

Next, for the length L of the waveguide 31, the _second dielectric when 1/4 of the in-tube wavelength during propagation of the first dielectric layer 133 at f ₂ = 70 GHz is 1.252 mm and f ₄ = 90 GHz. 1/4 of the guide wavelength during propagation of the layer 134 (air layer) is 1.277 mm, and the length L of the waveguide 31 is about 1.26 mm therebetween, thereby matching both frequencies and the vicinity thereof. be able to. Here, the in-tube wavelengths for the frequencies of f ₂ = 70 GHz and f ₄ = 90 GHz are matched to the two dielectric layers. However, the present invention is not limited to this, and if a plurality of frequencies covering the desired band are selected. It may be a combination of 60 and 90 GHz. In the case of a three-layer structure, 60, 75, 90 GHz or the like may be selected.

  The above example is a structural example in which a plurality of M = 2 dielectric layers are provided inside the waveguide 31. When this is generalized to M ≧ 2, it is as follows.

In other words, for a plurality of N (≧ M) frequencies f ₁ , f ₂ ,... F _N electromagnetic waves in the desired propagation frequency band of the millimeter wave band, the synthesis of the waveguide 31 composed of a plurality of M dielectric layers. When the impedance is Z _x1 , Z _x2 ,... Z _xN , the impedance of the waveguide 20 is Z _w1 , Z _w2 ,... Z _wN , _respectively , and the impedance Z1 of the microstrip line 10 is
Z _x1 = √ (Z1 × Z _w1 )
Z _x2 = √ (Z1 × Z _w2 )
......
Z _xN = √ (Z1 × Z _wN )
And the M frequencies of the plurality of N frequencies f ₁ , f ₂ ,... F _N are denoted by f _{a1 to} f _aM ,
The in-tube wavelength when the electromagnetic wave having the first frequency f _a1 propagates through the first dielectric layer among the plurality of M dielectric layers is λ _g1 ,
An in-tube wavelength when the electromagnetic wave having the second frequency f _a2 propagates through the second dielectric layer among the plurality of M dielectric layers is λ _g2 ,
......
An in-tube wavelength when an electromagnetic wave having the M-th frequency _faM propagates through the M-th dielectric layer among the plurality of M dielectric layers is λ _gM.
When the length L of the waveguide 31 is
L = λ _g1 / 4 = λ _{g2 /4=...=λ gM} / 4
The diameter of the waveguide 31 and the relative dielectric constant of the dielectric layer may be set so that

  However, in practice, the dielectric constant of the dielectric is uniquely determined by the material and cannot be set to an arbitrary value. Therefore, select a dielectric with low loss in the millimeter wave band and use the relative dielectric constant. Only the width a and the length L of the waveguide 31 need to be set so as to satisfy the above conditions.

  In the case of the basic structure described above, the emission of electromagnetic waves from the boundary between the microstrip line 10 and the transmission line converter 30 to the external space and the reflection at the boundary between the transmission line converter 30 and the waveguide 20 are completely eliminated. However, the deterioration of characteristics due to the radiated wave and the reflected wave is expected.

  FIG. 3 shows an example of a more practical transmission path conversion structure in which the influence of the radiated wave and the reflected wave is reduced. In the transmission line converter 30 ″ of this structural example, a radiation wave guide 35 is provided on the end surface of the upper metal wall 32a on the microstrip line 10 side among the metal walls 32a to 32d surrounding the dielectric 33.

  The radiated wave guide 35 is opposed to the dielectric substrate 11 of the microstrip line 10 in parallel, and is separated from the main conductor 12 by a predetermined distance from one side of the main conductor 12. The second metal wall 35b provided and the third metal wall 35c provided a predetermined distance apart on the other side of the main conductor 12 are formed in a U-shape, and the dielectric substrate 11, one end side of the main conductor 12 is surrounded by a predetermined length with respect to 11 to suppress the emission of electromagnetic waves from the boundary between the microstrip line 10 and the waveguide 31 to the external space, and the radiated wave is transmitted to the main conductor 12. A radiation wave guide path 36 is formed to guide to the other end side.

  A groove 37 having a depth corresponding to ¼ of the wavelength of the desired propagation frequency is formed on the inner circumference of the first metal wall 35a of the radiation wave guide 35 to prevent leakage of the radiation wave. It is provided in a direction orthogonal to the direction. The component that enters the groove 37 and the component that reciprocates through the groove 37 are reversed in phase and cancel each other, and leakage of radiation waves can be prevented.

  The groove 37 provided in the radiation wave guide 35 can prevent leakage of electromagnetic waves radiated from the boundary between the microstrip line 10 and the waveguide 31.

  Although only one groove 37 is shown here, a plurality of grooves having different depths are arranged in the length direction of the first metal wall 35a, so that leakage of electromagnetic waves radiated to the external space is broader. Can be prevented. Further, in this example, the radiation wave guide 35 that is formed in the U shape under the three metal walls 35a to 35c is used. However, the radiation wave guide 35 is a metal wall that is connected to one end side of the main conductor 12 in a predetermined manner. The radiation of the electromagnetic wave radiated from the boundary space of the waveguide 31 filled with the microstrip line 10 and the dielectric 33 to the external space is suppressed and the radiated wave radiated to the external space is The shape may be a shape that guides to the other end side, and the cross-sectional shape of the inner periphery may be a trapezoidal shape, a semicircular shape, or the like. Further, the groove 37 may be provided at a predetermined depth not only on the wall surface of the microstrip line 10 facing the dielectric substrate 11 but also on the entire inner periphery.

  On the other hand, when the width a of the waveguide 31 is 2.2 mm according to the above numerical example and the height b is the same as the height of the waveguide 21 of the waveguide 20 (1.55 mm), the second dielectric layer The thickness of (air layer) 134 is 1.25 mm obtained by subtracting the thickness of 0.3 mm of the first dielectric layer 133 from 1.55 mm. In this case, the diameter of the waveguide 31 is 2.2 × 1. 55 mm and the diameter of the waveguide WR-12, which is typically used for the millimeter wave band, is approximately 3.1 × 1.55 mm, so it is estimated that no large reflection occurs even in the direct connection state. .

  However, in the above numerical example, the thickness of the second dielectric layer 134 is more than four times the thickness of the first dielectric layer 133, and the height of the line at the boundary with the microstrip line 10 is It will change greatly, and reflection may occur by this influence.

  Therefore, in this embodiment, the thickness of the second dielectric layer 134 is set to be approximately the same as the thickness of the first dielectric layer 133, for example, and the thickness of the microstrip line 10 and the height dimension of the waveguide 31 are set. So that there is no extreme difference between the two.

  As a result, the height dimension of the waveguide 31 inevitably becomes smaller than the height dimension of the waveguide of the standard waveguide WR-12, and the difference in aperture from the waveguide 20 becomes a problem.

  Therefore, as shown in FIG. 3, the diameter of the one end side opening 21a of the waveguide 20 ′ is smaller than the standard diameter, and corresponds to the diameter of the other end side of the waveguide 31 (for example, 2.2 × 0.6 mm), a tapered portion 21b whose diameter gradually increases from the opening toward the other end (may be stepwise instead of linear as shown in the figure) (for example, up to a standard diameter), and a tapered portion A standard aperture 21c following 21b is formed to suppress reflection due to the aperture difference between the waveguide 31 and the waveguide 22.

  FIG. 4 shows a simulation result of obtaining transfer characteristics when the above numerical example is used in the transmission path conversion structure shown in FIG.

  In FIG. 4, the insertion loss is 1 dB or less and the reflection coefficient is −10 dB or less in the frequency range of 60 to 90 GHz, and between the microstrip line 10 and the waveguide 20 in a wide frequency range of the millimeter wave band. It can be confirmed that consistency is achieved.

  Further, FIG. 5 shows that the position of the microstrip line 10 is orthogonal to the length direction (Z direction) of the main conductor 12 on a plane (XZ plane) parallel to the dielectric substrate 11 with respect to the waveguide 31. FIG. 6 shows the transfer characteristics when the shift is made in the direction (X direction) (the amount of movement dx). FIG. 6 shows the position of the microstrip line 10 parallel to the dielectric substrate 11 with respect to the waveguide 31. The transfer characteristics when the main conductor 12 is shifted in the length direction (Z direction) on the surface (movement amount dz) are obtained.

  5 and 6, it can be seen that the reflection coefficient S11 is -10 dB or less even if it is deviated by about 0.2 mm in the X direction, and that the performance is secured even if it is deviated by about 0.5 mm in the Z direction. A general manufacturing error of a component of this size is about ± 10 μm, and the error is considered to be 100 μm or less even in the combination of the components. Therefore, the above conversion structure is also desired for a component and an assembly error. The performance can be maintained.

  In the transmission line conversion structure described above, a plurality of dielectric layers are provided in the waveguide 31 formed by being surrounded by the metal walls 32a to 32d. However, the structure of the waveguide 31 is arbitrary.

  For example, as shown in FIG. 7, a ground conductor 41 covering the entire top surface of a dielectric substrate 40 similar to the dielectric substrate 11 used in the microstrip line 10, and ground conductors 42, 43 covering both ends of the bottom surface. Are connected by metal posts 45 formed by through-hole processing, and two rows of metal posts 45 are provided at predetermined intervals, so that among the metal walls 32c and 32d forming the waveguide 31, A portion surrounding both sides of the first dielectric layer 133 can be formed. In this case, the interval between the metal posts 45 in the row is made sufficiently smaller than the wavelength of the electromagnetic wave propagating through the first dielectric layer 133, and the row interval is made to coincide with the width a described above. FIG. 8 shows a transmission line conversion structure in which the waveguide 31 is formed using the metal post 45. In this case, the ground conductor 41 of the dielectric substrate 40 is in contact with the metal wall 32a, and the ground conductors 42, 43 are shown. However, the metal walls 32c and 32d are in contact with each other.

  In general, since the thickness of the ground conductor 41 is negligibly small with respect to the substrate thickness, even if the central portion of the ground conductor 41 (the portion between the rows of the metal posts 45) is deleted, Since the metal wall 32a contacts, there is no problem.

  In each of the above embodiments, the transmission line converter 30 having the waveguide 31 formed with a plurality of dielectric layers is separated from the microstrip line 10 and the waveguides 20 and 20 '. As shown in FIG. 10, the first dielectric layer 133 may be formed to extend to the end of the dielectric substrate 11 of the microstrip line 10. 9 is a form corresponding to the structure shown in FIGS. 2 and 3, and FIG. 10 is a form corresponding to the structure using the metal post 45 in FIGS. 7 and 8, and FIG. 8 has a structure in which the ground conductor 41 on the upper surface side is divided into two ground conductors 41a and 41b in the same manner as the lower surface side, and the ground conductors 42 and 43 in FIGS. Are also used.

  Although not shown, at least a part of the metal walls 32a to 32d forming the waveguide 31 is formed integrally with the earth conductor 13 of the microstrip line 10 and the metal walls of the waveguides 20 and 20 '. Various modifications can be made to the specific structure. As one example, the metal wall 32b forming the waveguide 31 is extended to the microstrip line 10 side to be the ground conductor 13 that supports the dielectric substrate 11, and is extended to the waveguide 20 side. Various structures such as a lower metal wall can be adopted.

  In the above embodiment, the number M of dielectric layers is 2 and one of them is an air layer. However, a dielectric layer other than air may be used, and the number M of dielectric layers is 3 or more. It may be. In the above example, one of the plurality of dielectric layers formed in the waveguide is the same material and the same thickness as the dielectric substrate of the microstrip line 10, but the dielectric of the microstrip line 10 is used. A waveguide may be formed using a dielectric layer having a thickness different from that of the substrate.

  DESCRIPTION OF SYMBOLS 10 ... Microstrip line, 11 ... Dielectric substrate, 12 ... Main conductor, 13 ... Ground conductor, 20, 20 '... Waveguide, 21 ... Waveguide, 30, 30', 30 "... ... Transmission path converter, 31 ... Waveguide, 32 ... Metal wall, 33 ... Dielectric, 35 ... Radiation wave guide, 35a ... First wall, 35b ... Second wall, 35c ... Third wall 36... Radiation wave guide path 37... Groove 40. Dielectric substrate 41, 42, 43. Earth conductor 45. Metal post 133 133 First dielectric layer 134 Second dielectric layer

Claims (7)

It consists of a main conductor (12) formed on one side of the dielectric substrate (11) and an earth conductor (13) formed on the opposite side, and propagates an electromagnetic wave in the millimeter wave band in the length direction of the main conductor. In the millimeter waveband transmission line conversion structure for connecting the microstrip line (10) and the waveguide (20) capable of propagating millimeter wave electromagnetic waves,
A plurality of M dielectric layers (133, 134) having a waveguide structure in which a waveguide (31) having a predetermined diameter and a predetermined length is surrounded by a metal wall (32) and having different relative dielectric constants The microstrip line is formed so as to be continuous from one end to the other end of the waveguide, and one end face of the waveguide is joined to the end face of the dielectric substrate on one end side of the main conductor of the microstrip line. Propagating the electromagnetic wave in the millimeter wave band with one end side of the waveguide, and joining the other end face of the waveguide to the one end side opening face of the waveguide, A millimeter-wave band transmission line conversion structure characterized in that the millimeter-wave band electromagnetic wave is propagated between one end side of the waveguide. Desired propagation frequency _{f 1,} f 2 of a plurality N (≧ M) having different within the frequency band, ...... _f the combined impedance of the waveguide for electromagnetic waves _{N Z x1, Z x2, ......} Z xN, the waveguide _Are the impedances Z _w1 , Z _w2 ,... Z _wN and the impedance Z1 of the microstrip line,
Z _x1 = √ (Z1 × Z _w1 )
Z _x2 = √ (Z1 × Z _w2 )
......
Z _xN = √ (Z1 × Z _wN )
And the M frequencies of the plurality N of frequencies f ₁ , f ₂ ,... F _N are denoted by f _{a1 to} f _aM ,
An in-tube wavelength when an electromagnetic wave having a first frequency f _a1 propagates through the first dielectric layer of the plurality of dielectric layers is λ _g1 ,
An in-tube wavelength when an electromagnetic wave having a second frequency f _a2 propagates through the second dielectric layer of the plurality of dielectric layers is λ _g2 ,
......
An in-tube wavelength when an electromagnetic wave having an Mth frequency _faM propagates through the Mth dielectric layer of the plurality of dielectric layers is λ _gM.
When the length L of the waveguide is
L = λ _g1 / 4 = λ _{g2 /4=...=λ gM} / 4
The millimeter-wave band transmission line conversion structure according to claim 1, wherein the diameter of the waveguide and the relative dielectric constant of each dielectric layer are set so that   The plurality M is 2, the first dielectric layer is made of a dielectric having a relative dielectric constant greater than 1, and the second dielectric layer is an air layer having a relative dielectric constant of 1. The millimeter-wave band transmission line conversion structure according to claim 1 or 2. One end side of the main conductor of the microstrip line is surrounded by a metal wall (35a to 35c) for a predetermined length, and from a boundary part between the microstrip line and the waveguide in which the plurality of dielectric layers are formed. A radiation wave guide (35) forming a radiation wave guide path (36) for guiding the radiation wave radiated to the external space to the other end of the main conductor;
The groove (37) having a depth corresponding to ¼ of the wavelength of the desired propagation frequency is provided on the inner periphery of the metal wall of the radiation wave guide for preventing leakage of the radiation wave. The millimeter-wave band transmission path conversion structure according to any one of 1 to 3.   Metal posts (45) for connecting a part of the metal wall surrounding the waveguide to the ground conductors (41, 42, 43) provided on both surfaces of the dielectric substrate (40) by through-hole processing at a predetermined interval. The millimeter-wave band transmission line conversion structure according to any one of claims 1 to 4, wherein the millimeter-wave band transmission line conversion structure is formed side by side.   6. The millimeter wave band transmission line conversion structure according to claim 1, wherein one of the plurality of dielectric layers is formed by extending a dielectric substrate of the microstrip line.   The diameter of one end of the waveguide is set to a size corresponding to the diameter of the waveguide in which the plurality of dielectric layers are formed, and the diameter increases toward the other end. The millimeter-wave band transmission line conversion structure according to any one of claims 1 to 6.

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