JP6835661B2 - High frequency transmission line - Google Patents

Description

The present invention relates to a high frequency transmission line in which a signal line having a bent portion is formed on the surface of a substrate.

Since it is difficult to secure a sufficient wiring area for the high-frequency transmission line due to the recent miniaturization of modules and the increase in mounting density, a bent transmission line shape is adopted instead of a symmetrical linear structure. There are things that must be done.
In a high-frequency transmission line having such a bent portion, the characteristic impedance changes at the bent portion. As a result, the characteristic impedance becomes discontinuous between the straight portion and the bent portion, and the transmission characteristic deteriorates. In some cases, a standing wave with a bent portion as a reflection end is generated to form a stub structure, and only a specific frequency may be blocked. At the bent portion, the electric field coupling distribution becomes asymmetric with respect to the transmission direction of the signal line, so that the characteristic impedance changes.

Conventionally, in such a high-frequency transmission line, as a technique for adjusting the characteristic impedance between a straight portion and a bent portion, the characteristic impedance of the bent portion is adjusted by changing the line width of the signal line at the bent portion. Those have been proposed (see, for example, Non-Patent Document 1).
7A and 7B are configuration examples showing a bent portion of a conventional microstrip line, FIG. 7A shows a front view, and FIG. 7B shows a back view. In the configuration example of this microstrip line, a signal line 52 through which a high frequency signal flows is formed on the front surface of the substrate 51, and a ground plane 53 to which a ground potential is applied is formed on the back surface of the substrate 51. Has been done. A bent portion B in which the signal line 52 bends at a right angle is provided in the middle of the signal line 52, and a notch 54 is formed at a convex side angle of the bent portion B.

FIG. 8 is a configuration example showing a bent portion of a conventional coplanar line, FIG. 8A shows a front view, and FIG. 8B shows a back view. In this configuration example of the coplanar wire, a signal line 62 through which a high frequency signal flows is formed on the surface of the substrate 61, and surface grounds 65 are formed on both sides thereof. Further, on the back surface of the substrate 61, a ground plane 63 to which a ground potential is applied is formed on the entire back surface. A bent portion B in which the signal line 62 bends at a right angle is provided in the middle of the signal line 62, and a notch portion 64 is formed at a convex side angle of the bent portion B.

In each of these high-frequency transmission line configuration examples, among the bent portions of the signal line formed on the substrate surface, the line width of the signal line at the bent portion is narrowed by forming a notch at the convex side angle. is there. Thereby, the characteristic impedance of the bent portion can be adjusted.

B.C. Wadell, "Transmission Line Design Handbook", 1991, Artech House Publishers., Pp.289

In general, in a high-frequency transmission line, it is difficult to form a grounding structure symmetrical with respect to the signal line at the bent portion. Therefore, in the prior art, the characteristic impedance of the bent portion is changed by adjusting the line width of the signal line at the bent portion, and the characteristic impedance of the straight portion is adjusted.
However, according to the configuration of such a conventional technique, since the characteristic impedance of the bent portion is adjusted by narrowing the line width of the signal line, the influence of the pattern tolerance at the time of manufacturing is large, and the characteristic impedance is the design value. There was a problem that it was easy to deviate greatly from. Further, there is a problem that the current capacity of the signal line is reduced by the amount that the line width is narrowed at the bent portion.

An object of the present invention is to solve such a problem, and an object of the present invention is to provide a high-frequency transmission line capable of adjusting the characteristic impedance of a bent portion without changing the line width of the signal line at the bent portion.

In order to achieve such an object, the high-frequency transmission line according to the present invention includes a substrate, a signal line formed on the front surface of the substrate, and a ground plane composed of a ground conductor formed on the back surface of the substrate. A high-frequency transmission line provided, wherein the signal line has a bent portion that connects two straight portions having different extension directions to each other, and the ground plane is located immediately below a convex side angle of the bent portion. The ground conductor has an opening that is selectively removed.

Further, in the high-frequency transmission line according to the present invention, the opening is located on a virtual line whose apex passes through the convex and concave angles of the bent portion in a plan view, and the base is the virtual line. Isosceles triangle or substantially isosceles triangle whose apex angle is substantially equal to the bending angle of the bent portion .

Further, one configuration example of the high-frequency transmission line according to the present invention is in a region on the convex side corner side of the bent portion among the electric capacitance components generated between the signal line of the bent portion and the ground plane. The first electric capacity component generated in a certain convex side portion is smaller than the second electric capacity component generated in the concave side portion which is a region on the concave side corner side of the bent portion .

Further, in one configuration example of the high-frequency transmission line according to the present invention, the signal line is composed of a microstrip line or a coplanar line having a surface ground formed on the surface of the substrate.

Further, in one configuration example of the high-frequency transmission line according to the present invention, the signal line is composed of a pair of differential lines in which a positive-phase signal line and a negative-phase signal line are arranged in parallel with each other, and the opening is formed. It is formed directly below the convex side angle of one of the positive phase signal line and the reverse phase signal line located on the convex side in the bent portion.

Further, in one configuration example of the high-frequency transmission line according to the present invention, the substrate is composed of a laminated ceramic substrate in which a plurality of ceramic layers are laminated.

According to the present invention, the characteristic impedance at the convex side portion and the concave side portion of the bent portion can be adjusted without changing the line width of the signal line at the bent portion. Therefore, it is possible to make the characteristic impedance continuous between the straight portion and the bent portion, and as a result, it is possible to suppress the deterioration of the transmission characteristic.

It is explanatory drawing which shows the structure of the high frequency transmission line which concerns on 1st Embodiment. It is explanatory drawing which shows the main part structure of FIG. This is a modified example of the opening. It is explanatory drawing which shows the structure of the high frequency transmission line which concerns on 2nd Embodiment. It is explanatory drawing which shows the structure of the high frequency transmission line which concerns on 3rd Embodiment. It is explanatory drawing which shows the structure of the high frequency transmission line which concerns on 4th Embodiment. This is a configuration example showing a bent portion of a conventional microstrip line. This is a configuration example showing a bent portion of a conventional coplanar line.

Next, an embodiment of the present invention will be described with reference to the drawings.
[First Embodiment]
First, the high-frequency transmission line 10 according to the first embodiment of the present invention will be described with reference to FIGS. 1 and 2. 1A and 1B are explanatory views showing a configuration of a high-frequency transmission line according to the first embodiment, FIG. 1A is a surface view, FIG. 1B is a sectional view taken along the line AA of FIG. 1A. , FIG. 1 (c) is a back view. 2A and 2B are explanatory views showing a configuration of a main part of FIG. 1, FIG. 2A is a surface view of the main part, FIG. 2B is a sectional view taken along line BB of FIG. 2A, and FIG. ) Is an equivalent circuit diagram of a high frequency transmission line.

As shown in FIG. 1, the high-frequency transmission line 10 includes a substrate 11, a signal line 12 linearly formed on the front surface of the substrate 11, and a ground plane 13 composed of a ground conductor formed on the back surface of the substrate 11. I have. The high-frequency transmission line 10 is suitable for, for example, an electronic device or an electronic component in which a high-speed electric signal of 10 GHz to 100 GHz or less propagates on a dielectric substrate.

The substrate 11 is a high-frequency substrate in which conductor layers such as metal thin films are formed on the upper and lower surfaces (front surface and back surface) of the dielectric layer. For example, from a laminated ceramic substrate in which a plurality of ceramic layers are laminated. It is configured.

The signal line 12 is a microstrip line made of a thin film conductor such as metal and having a constant line width W. In the middle of the signal line 12, a bent portion 12Z that changes the extending direction of the line to a predetermined angle is provided, whereby two straight portions 12X and 12Y having different extending directions are connected to each other by the bent portion 12Z. Has been done. In the example of FIG. 1, a straight line portion 12X extending in the horizontal direction in a plan view and a straight line portion 12X extending in a vertical direction in a plan view are connected to each other by a bent portion 12Z. Here, a case where the bending angle between the straight portion 12X and the straight portion 12Y in the bending portion 12Z is a right angle (90 °) is shown as an example, but the present invention is not limited to this. The present invention can be similarly applied when the bending angle is larger or smaller than 90 °.

The ground plane 13 has an opening 14 in which the grounding conductor located directly below the convex side angle (outer edge angle) P of the bent portion 12Z is selectively removed.
The opening 14 has a shape that is line-symmetric with respect to the virtual line M, and has a base S formed of a straight line that is orthogonal to the virtual line M and intersects the bent portion 12Z in a plan view. The virtual line M is a straight line that passes through the convex side angle P and the concave side angle (inner edge angle) Q of the bent portion 12Z in a plan view.

In the example of FIG. 1, an example in which the opening 14 is composed of a right-angled isosceles triangle is shown, and the apex V of the right-angled isosceles triangle is located on the virtual line M outside the bent portion 12Z from the convex side angle P. The base S of the right-angled isosceles triangle is orthogonal to the virtual line M and intersects the bent portion 12Z. As a result, the opening 14 is located directly below the convex side angle P of the bent portion 12Z.

In the bent portion 12Z of the signal line 12, an electric capacitance component is generated between the signal line 12 on the front surface and the ground plane 13 on the back surface with the dielectric layer of the substrate 11 interposed therebetween. Here, the electric capacitance component generated in the convex side portion 12P, which is the region on the convex side angle P side of the bent portion 12Z, is defined as CP (first electric capacitance component), and the concave side angle Q side of the bent portion 12Z. The electric capacity component generated in the concave side portion 12Q, which is a region, is defined as CQ (second electric capacity component).

As a result, as shown in FIG. 2C, the equivalent circuit of the bent portion 12Z is represented by a T-shaped four-terminal circuit in which the parallel circuit of CP and CQ is sandwiched between the two inductances LX and LY. The end portion TX is a connection point with the straight portion 12X of the bent portion 12Z, and the inductance LX is the inductance of the bent portion 12Z on the straight portion 12X side. Further, the end portion TY is a connection point with the straight portion 12Y of the bent portion 12Z, and the inductance LY is the inductance of the bent portion 12Z on the straight portion 12Y side.

Generally, when the opening 14 is not present, CP> CQ at the bent portion 12Z, as shown in Non-Patent Document 1. Therefore, in the signal line 12, the characteristic impedance is different between the convex side portion 12P and the concave side portion 12Q of the bent portion 12Z, and the characteristic impedance is not satisfied between the straight portions 12X and 12Y and the bent portion 12Z. It becomes continuous and causes deterioration of transmission characteristics.

In the present embodiment, attention is paid to the bias of the electric capacitance components CP and CQ in the convex side portion 12P and the concave side portion 12Q of the bent portion 12Z, and the opening 14 is provided directly below the bent portion 12Z. .. As a result, the distance between the convex side angle P and the ground plane 13 becomes larger than the distance between the concave side angle Q and the ground plane 13, and the situation of CP <CQ can be obtained at the bent portion 12Z.

Therefore, according to the present embodiment, the characteristic impedance at the convex side portion 12P and the concave side portion 12Q of the bent portion 12Z can be adjusted without changing the line width of the signal line 12 at the bent portion 12Z. Therefore, it is possible to make the characteristic impedance continuous between the straight portions 12X and 12Y and the bent portion 12Z, and as a result, it is possible to suppress the deterioration of the transmission characteristics.

In FIG. 1, the case where the opening 14 is formed of a right-angled isosceles triangle and the length L of the two isosceles triangles is larger than the line width W of the signal line 12 is shown as an example, but the case is limited to this. Instead, it may be an isosceles triangle or a substantially isosceles triangle whose apex angle θ is substantially equal to the bending angle θZ of the bent portion 12Z. Further, the shape and size of the opening 14 may be arbitrarily designed so that the characteristic impedance is continuous between the straight portions 12X and 12Y and the bent portion 12Z.

FIG. 3 is a modified example of the opening. FIG. 3A shows a case where the shape of the opening 14 is the above-mentioned right-angled isosceles triangle. That is, the opening 14 has a shape that is line-symmetric with respect to the virtual line M, the apex V is located on the virtual line M outside the bending portion 12Z from the convex side angle P, and the base S is the virtual line M. It intersects (crosses) with the bent portion 12Z.

In general, it is desirable that the apex angle θ of the isosceles triangle is substantially the same as the bending angle θZ of the bent portion 12Z. As a result, the two isosceles triangles have substantially the same extension direction as the straight portions 12X and 12Y, and the equilateral sides and the convex end portions of the bent portion 12Z are parallel to each other, and the distance between them becomes substantially constant. Therefore, it is possible to suppress the generation of the electric capacity component CP in a partially biased manner, and the shape and size of the opening 14 can be easily designed in order to obtain the intended CP.

FIG. 3B shows a trapezoid as the shape of the opening 14. This trapezoid is obtained by cutting out the apex V side of the right-angled isosceles triangle shown in FIG. 3A in parallel with the base S. As a result, almost the same effect as that of a right-angled isosceles triangle can be obtained.

FIG. 3C shows an isosceles triangle having an apex angle θ larger than a right angle as the shape of the opening 14. Further, FIG. 3D uses an isosceles triangle whose apex angle θ is smaller than a right angle as the shape of the opening 14. As a result, even if the bending angle θZ of the bent portion 12Z is other than a right angle, a good effect can be obtained.

FIG. 3E shows a plano-convex shape as the shape of the opening 14. This shape is obtained by cutting out the apex V side of a right-angled isosceles triangle whose apex angle θ is larger than a right angle, as shown in FIG. 3C, with an arc that is axisymmetric with respect to the virtual line M. As a result, almost the same effect as that of a right-angled isosceles triangle can be obtained.

FIG. 3F shows an isosceles triangle as the shape of the opening 14. This shape is non-axisymmetric with respect to the virtual line M, and the vertex V does not necessarily have to be on the virtual line M. According to this shape, the size of the generated electric capacitance component CP can be adjusted between the straight portion 12X side and the straight portion 12Y side. As a result, the reflection characteristics of the high-frequency signals in the linear portions 12X and 12Y can be adjusted individually, and the substrates (not shown) connected via the linear portions 12X and 12Y are different, and the reflection characteristics are different. It is effective when they are different.

[Second Embodiment]
Next, the high-frequency transmission line 10 according to the second embodiment of the present invention will be described with reference to FIG. 4A and 4B are explanatory views showing the configuration of a high-frequency transmission line according to the second embodiment, FIG. 4A is a surface view, FIG. 4B is a sectional view taken along the line CC of FIG. 4A. , FIG. 4 (c) is a back view.
The present embodiment is different from FIG. 1 in that the notch 12R is provided at the convex side angle P of the bent portion 12Z, but other configurations such as the opening 14 provided on the back surface of the substrate 11 are used. , The same as in FIG.

That is, in the present embodiment, as shown in FIG. 4, the convex side angle P of the bent portion 12Z has a cutout portion 12R in which a part of the bent portion 12Z is cut out along a direction orthogonal to the virtual line M. It is provided.
As a result, the line width at the bent portion 12Z changes, and the characteristic impedance can be adjusted. Therefore, the characteristic impedance can be adjusted by the size and shape of the notch 12R in addition to the opening 14, and the degree of freedom in design can be greatly expanded.

[Third Embodiment]
Next, the high-frequency transmission line 10 according to the third embodiment of the present invention will be described with reference to FIG. 5A and 5B are explanatory views showing a configuration of a high-frequency transmission line according to a third embodiment, FIG. 5A is a surface view, and FIG. 5B is a sectional view taken along line DD of FIG. 5A. , FIG. 5 (c) is a back view.
This embodiment is applied to a coplanar line with a back surface gland instead of the microstrip line of FIG. 1, but other configurations such as an opening 14 provided on the back surface of the substrate 11 are shown in FIG. Is similar to.

That is, in the present embodiment, as shown in FIG. 4, the signal line 12 formed on the surface of the substrate 11 is composed of a coplanar line, and a gap having a constant width with the signal line 12 is provided on both sides of the signal line 12. A surface ground 15 is formed so as to sandwich the surface.
As a result, even if the signal line 12 is a coplanar line with a back ground, the same effect as that of the microstrip line described above can be obtained.

[Fourth Embodiment]
Next, the high-frequency transmission line 10 according to the fourth embodiment of the present invention will be described with reference to FIG. 6A and 6B are explanatory views showing a configuration of a high-frequency transmission line according to a fourth embodiment, FIG. 6A is a surface view, and FIG. 6B is a sectional view taken along line EE of FIG. 6A. , FIG. 6C is a back view.
In this embodiment, as the microstrip line of FIG. 1, the signal line 12 is composed of a differential line.

That is, in the present embodiment, as shown in FIG. 6, the signal line 12 is composed of a pair of differential lines in which the positive phase signal line 16 and the negative phase signal line 17 are arranged in parallel with each other. The positive phase signal line 16 is a signal line through which a positive phase signal flows, and linear portions 16X and 16Y are connected to each other by bending portions 12Z. The reverse phase signal line 17 is a signal line through which a reverse phase signal having a phase opposite to that of the positive phase signal flows, and the linear portions 17X and 17Y are connected to each other by the bending portion 12Z.

In this case, the positive phase signal line 16 and the negative phase signal line 17 can be regarded as one signal line 12. Therefore, of the ground plane 13 on the back surface of the substrate 11, the position is directly below the convex side angle P with respect to the bent portion 12Z of the signal line 12 including the positive phase signal line 16 and the negative phase signal line 17, that is, on the convex side in the bent portion 12Z. An opening 14 is formed immediately below the convex side angle P of the reverse phase signal line 17. As a result, even if the signal line 12 is a differential line, the same effect as described above can be obtained.

In addition, it is conceivable that the line widths of the positive phase signal line 16 and the negative phase signal line 17 are wide, and the electric capacitance component may be biased to some extent in the convex side region and the concave side region of each bent portion. In such a case, an opening 14 may be formed in the ground plane 13 on the back surface of the substrate 11 just below the convex side corners of the positive phase signal line 16 and the negative phase signal line 17, respectively. As a result, even if the signal line 12 is a differential line, the same effect as described above can be obtained.

[Extension of Embodiment]
Although the present invention has been described above with reference to the embodiments, the present invention is not limited to the above embodiments. Various changes that can be understood by those skilled in the art can be made to the structure and details of the present invention within the scope of the present invention. In addition, each embodiment can be implemented in any combination within a consistent range.

10 ... High frequency transmission line, 11 ... Substrate, 12 ... Signal line, 12P ... Convex side part, 12Q ... Concave side part, 12R ... Notch part, 12X, 12Y ... Straight line part, 12Z ... Bending part, 13 ... Ground plane, 14 ... Opening, 15 ... Surface ground, 16 ... Positive phase signal line, 16X, 16Y ... Straight line part, 17 ... Reverse phase signal line, 17X, 17Y ... Straight line part, M ... Virtual line, P ... Convex side angle, Q ... Concave side Corner, S ... bottom, V ... vertex, CP, CQ ... electrical capacity component, LX, LY ... inductance, TX, TY ... end.

Claims (5)

A high-frequency transmission line including a substrate, a signal line formed on the front surface of the substrate, and a ground plane formed of a ground conductor formed on the back surface of the substrate.
The signal line has a bent portion that connects two straight portions having different extension directions to each other.
The ground plane, have a opening the ground conductor is selectively removed located immediately below the convex side angle of the bent portion,
The opening is located on a virtual line whose apex passes through the convex and concave corners of the bent portion in a plan view, the base intersects the virtual line, and the apex angle is the bending of the bent portion. A high-frequency transmission line characterized by forming an isosceles triangle or a substantially isosceles triangle having approximately the same angle. In the high-frequency transmission line according to claim 1,
Of the electric capacitance components generated between the signal line of the bent portion and the ground plane, the first electric capacitance component generated in the convex side portion of the bent portion on the convex side corner side is described above. A high-frequency transmission line characterized in that it is smaller than the second electric capacitance component generated in the concave side portion of the bent portion on the concave side corner side. In the high-frequency transmission line according to claim 1 or 2.
The signal line is a microstrip line or a high-frequency transmission line having a surface ground formed on the surface of the substrate. In the high-frequency transmission line according to any one of claims 1 to 3.
The signal line consists of a pair of differential lines in which positive phase signal lines and negative phase signal lines are arranged in parallel with each other.
The opening is formed immediately below the convex side angle of one of the positive phase signal line and the negative phase signal line located on the convex side in the bent portion. line. In the high-frequency transmission line according to any one of claims 1 to 4.
The substrate is a high-frequency transmission line characterized by being composed of a laminated ceramic substrate in which a plurality of ceramic layers are laminated.

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