JP5519328B2 - High-frequency transmission line substrate - Google Patents

Description

  The present invention relates to a high-frequency transmission line substrate used in a frequency band of several tens of GHz, and in particular, high-frequency transmission capable of suppressing deterioration in transmission characteristics in a conversion portion between a microstrip line and a grounded coplanar line. It relates to a line substrate.

  As a line for transmitting a high frequency signal of several tens of GHz, a microstrip line or a grounded coplanar line is known. Which one to select when forming these transmission lines on an insulating substrate depends on the external conditions of the insulating substrate. For example, when the outside of the insulating substrate is a coaxial connector, a microstrip line is selected, and when the outside of the insulating substrate is an IC, a grounded coplanar line is often selected.

  The microstrip line has a structure in which a conductive foil or the like is deposited on the front and back surfaces of a dielectric substrate. The front surface conductive foil forms a signal line conductor, and the back surface conductive foil forms a ground layer. ing. Note that the wider the width of the signal line conductor, the smaller the characteristic impedance of the microstrip line. When the microstrip line is connected to the coaxial connector, the signal line conductor and the ground layer are connected to the coaxial core line and the ground, respectively.

  On the other hand, a signal line conductor and ground conductors arranged on both sides of the signal line conductor are formed on the surface of a dielectric base material using a conductor foil or the like, which is called a coplanar line. Furthermore, the one in which the ground layer is formed on the back surface of the dielectric substrate is particularly called a grounded coplanar line. When the outside of the insulating substrate is an IC, the grounding conductor is formed on the same plane as the signal line conductor because the grounding pad on the top surface of the IC and the grounding conductor of the substrate must be connected by wire bonding or the like. In many cases, a grounded coplanar line is used as a transmission line.

  When connecting a microstrip line and a grounded coplanar line, in order to reduce transmission loss, a method of providing a conversion unit between the two and smoothly changing the structure at the conversion unit is used. However, it is very difficult to reduce transmission loss in a wide frequency band, and various inventions and devices have been proposed for this purpose.

For example, in Patent Document 1, a component having a grounded coplanar line or a coplanar line type terminal used in the millimeter wave region and a component having a microstrip line type terminal are connected under the name “conversion line”. The invention regarding the improvement of the conversion line for this purpose is disclosed.
In the invention disclosed in Patent Document 1, the line width of the strip conductor of the microstrip line is made larger than that of the center conductor of the grounded coplanar line, and the taper is such that the line width gradually changes between the center conductor and the strip conductor. In addition, the distance from the ground layer on both sides of the tapered conductor portion (corresponding to the above-mentioned ground conductor) is changed in the same way. The structure is shifted to the grounded coplanar line side from the spreading starting point of the conductor.
According to such a structure, since the characteristic as a coplanar line can be gradually reduced while suppressing a change in characteristic impedance in the tapered conductor portion, signal reflection and insertion loss can be reduced even in a high frequency region of millimeter waves. Can be small.

Patent Document 2 discloses an invention relating to a “high-frequency signal transmission board” that can prevent high-frequency characteristics from deteriorating and allow a high-frequency signal to pass therethrough.
The invention disclosed in Patent Document 2 is a high-frequency signal transmission board having a ground dead coplanar line and a microstrip line, in which a plurality of vias are arranged in a direction away from the signal conductor line and extended from a ridge line part of the board. A notch portion extending from the ridge line portion to the first ground conductor film, leaving a proximity portion of the signal conductor line of the first ground conductor film, a via peripheral portion including the via, and a connecting portion connecting this and the proximity portion. The structure is formed.
In the high-frequency signal transmission substrate having such a structure, a notch portion is provided in a portion of the first ground conductor film where a stub may be generated in the vicinity of the ridge line portion of the substrate. It is possible to prevent the deterioration of characteristics such as a decrease in characteristics and an increase in the ratio of energy radiation.

Japanese Patent No. 3580667 JP 2008-147757 A

  However, in the invention disclosed in Patent Document 1 which is the above-described prior art, a stub in a region where current does not easily flow is present in the ground layer (corresponding to the above-described ground conductor). There was a problem that the characteristic of the transmission coefficient S21 to be reduced and the ratio of energy radiation were increased.

  Further, in the invention disclosed in Patent Document 2, transmission that occurs when a return current moves between the ground conductor and the ground layer through a via in the vicinity of the conversion portion of the microstrip line and the grounded coplanar line. There was a problem that the loss could not be reduced sufficiently.

  The present invention has been made in response to such a conventional situation, and a return current is generated between a ground conductor and a ground layer via a via in the vicinity of a conversion portion of a microstrip line and a grounded coplanar line. An object of the present invention is to provide a high-frequency transmission line substrate capable of suppressing transmission loss that occurs when moving and preventing deterioration of transmission characteristics.

In order to achieve the above-mentioned object, the invention according to claim 1 is provided symmetrically with a first signal line conductor formed on one surface of a dielectric substrate and sandwiching the first signal line conductor. A pair of first grounding conductors, a second grounding conductor extending from the pair of first grounding conductors in a direction away from the first signal line conductor, and the other surface of the substrate And a grounded coplanar line having a plurality of first vias and second vias that respectively connect the ground layer to the first ground conductor and the second ground conductor; and a first signal A microstrip line having a second signal line conductor connected to the line conductor via the conversion unit and a ground layer, and the first ground conductor is provided along the first signal line conductor. The second ground conductor has an arcuate outline and is closest to the converter The via land is formed so as to surround the opening of the first via and the second via with a predetermined width, and a connection line for connecting the via lands. The connection line is determined by the diameter of the outline of the via land. Is formed so as to have a narrow width.
In the high-frequency transmission line substrate having such a structure, since the distance between the return current flowing along the edge of the via land or the connection line and the second via is short, the return current can easily flow to the second via. Has an effect. In this case, a phenomenon that a part of the energy of the return current is radiated to the space hardly occurs. Moreover, since the 1st grounding conductor is not provided in the ridgeline part vicinity of a base material, there is no possibility that a stub will generate | occur | produce.

According to a second aspect of the present invention, in the high-frequency transmission line substrate according to the first aspect, the width of the connection line is twice the width of the via land. In the specification of the present application, “the width of the connection line is twice the width of the via land” includes the case of “substantially twice”.
In the high-frequency transmission line substrate having such a structure, the energy of the return current flowing through the second ground conductor is further maintained as compared with the invention according to claim 1 while maintaining the function of the connection line for conducting between the via lands. It has an effect that a part of it is not easily radiated into the space.

  According to the high-frequency transmission line substrate of the first aspect of the present invention, it is possible to reduce the transmission loss in the conversion part of the microstrip line and the grounded coplanar line, and to suppress the deterioration of the transmission characteristics.

  Moreover, according to the high-frequency transmission line substrate of claim 2 of the present invention, the effect of the invention of claim 1 is further exhibited.

(A) is a top view of the principal part of the Example of the high-frequency transmission line board | substrate which concerns on embodiment of this invention, (b) is XX arrow sectional drawing of the figure (a). (A) And (b) is the elements on larger scale of Drawing 1 (a). (A) And (b) is a figure which shows the modification of a present Example. (A) And (b) is the figure which showed typically the behavior of the return current in the transmission line board | substrate for high frequencies of a prior art and a present Example, respectively. (A) And (b) is a top view of the principal part of the transmission line board for high frequencies concerning a prior art. (A) And (b) is the result of having calculated | required transmission coefficient S21 about the transmission line board | substrate for high frequency of a prior art by numerical analysis. (A) And (b) is the result of having calculated | required transmission coefficient S21 by the numerical analysis about the transmission line board | substrate for high frequencies of a present Example.

  An example of the high-frequency transmission line substrate according to the embodiment of the present invention will be specifically described in comparison with the prior art.

The structure of the high-frequency transmission line substrate according to the present invention and the prior art will be described with reference to FIGS.
Fig.1 (a) is a top view of the principal part of the Example of the high-frequency transmission line board | substrate based on Embodiment of this invention, FIG.1 (b) is a XX arrow directional cross section of Fig.1 (a). FIG. In FIG. 1B, only the GND via 9a is shown and the GND via 9b is not shown, but the GND via 9b has the same cross-sectional structure as the GND via 9a. 2 (a) and 2 (b) are partial enlarged views of FIG. 1 (a), and FIGS. 3 (a) and 3 (b) are diagrams showing modifications of the present embodiment.

  As shown in FIGS. 1A and 1B, in the high-frequency transmission line substrate 1a of the present embodiment, a base material 2 formed by laminating one or more dielectrics such as ceramics and plastics. A signal line conductor 3 composed of a strip conductor 3a and a center conductor 3b and ground conductors 4a and 4b connected to each other through the conversion portion 8 are formed on the surface 2a of the substrate 2 and a ground layer 5 is formed on the back surface 2b of the substrate 2. Is formed as an island shape or a solid pattern on almost the entire surface. That is, the high-frequency transmission line substrate 1 is composed of a center conductor 3b, ground conductors 4a and 4a and ground conductors 4b and 4b that are symmetrically formed with the center conductor 3b interposed therebetween, and a grounded layer 5. The coplanar line 7, the strip conductor 3 a, and the microstrip line 6 constituted by the ground layer 5 are provided.

A plurality of through holes 2c are formed in the base material 2 from the ground conductors 4a and 4a and the ground conductors 4b and 4b toward the ground layer 5, and a metal conductor 10 is bonded to the inner wall surface of the through hole 2c. Thus, GND vias 9a and 9b are formed. That is, the ground conductors 4a and 4a and the ground conductors 4b and 4b and the ground layer 5 are electrically connected via the GND vias 9a and 9b, respectively.
The ground conductors 4b and 4b are extended from the ground conductors 4a and 4a in the direction away from the center conductor 3b in the vicinity of the converter 8, and the GND vias 9a are arranged at substantially equal intervals along the center conductor 3b. ing.

As shown in FIG. 2A, the strip conductor 3a is wider than the center conductor 3b, and the conversion portion 8 is formed so as to widen from the center conductor 3b toward the strip conductor 3a. The ground conductor 4a, 4a are formed so that the distance W ₂ is substantially equal to the distance W ₁ to the center conductor 3b for converting unit 8. On the other hand, the ground conductor 4b, 4b are outline is an arc shape, the closest GND vias 9a to the converter 8 (hereinafter, referred to as GND vias 14 as required.) And a width _{D 2} of the opening of the GND vias 9b The via land 12 is formed so as to surround the via land 12 and the connection line 13 that connects the adjacent via lands 12 to each other. The width D ₂ of the via land 12 is substantially equal to the width D ₁ of the ground conductor 4a. D ₃ is approximately twice the width D ₂ of the via land 12. Further, as shown in FIG. 2B, an angle α formed by a straight line (hereinafter referred to as array lines 11a and 11b) passing through the central axes of the GND vias 9a and 9b in a plan view of the substrate 2 is 90 degrees. It has become. The high-frequency transmission line substrate of the present invention is not limited to the structure shown in FIG. 1 or FIG. 2, and includes, for example, four GND vias 9b like the high-frequency transmission line substrate 1b shown in FIG. It can also be an installed structure. 3 (a) and 3 (b) correspond to FIGS. 1 (a) and 2 (a), respectively, and detailed description thereof is omitted. In addition, six or more GND vias 9b may be installed, and the number of GND vias 9b is not limited to one, and may be two or more.

Next, the operation of the high-frequency transmission line substrate 1a will be described with reference to FIG.
FIGS. 4A and 4B are diagrams schematically showing the behavior of the return current in the high-frequency transmission line substrate of the prior art and this example, respectively. In addition, the same code | symbol is attached | subjected about the component shown in FIG. 2, and the description is abbreviate | omitted. Further, the circle of FIG. 4 the high-frequency transmission line of the prior art shown in (a) the substrate 51a has a width D ₃ is via land 12 of the connection line 13 in the high-frequency transmission line substrate 1a of the present embodiment (FIG. 2 (a)) It is equal to the diameter D ₄ of the arc-shaped outline (FIG. 2A), and the outline of the via land 12 of the GND via 9b is formed in a rectangular shape.
As shown in FIG. 4A, in the high-frequency transmission line substrate 51a, a part of the return current flowing to the ground conductor 4b along the edge of the ground conductor 4a as indicated by the arrow A is indicated by the arrow B. So as to flow to GND vias 14 and 9b. However, between the GND via 14 and the GND via 9b, the distance between the return current flowing along the edge of the ground conductor 4b and the GND vias 14 and 9b becomes long, and the return current is in any of the GND vias 14 and 9b. It becomes difficult to flow. Therefore, a part of the energy of the return current is radiated to the space as indicated by the arrow C. As a result, transmission loss in the converter 8 increases.

On the other hand, the high frequency transmission line substrate 1a of the present embodiment, narrower than the width _{D 3} is the diameter _{D 4} of the arcuate outline of the via land 12 of the connection line 13 (FIG. 2 (a)), the GND vias 9b via land Since the outer contour line of 12 is formed in an arc shape, as shown by an arrow E in FIG. 4B, the edge of the via land 12 or the connection line 13 is also between the GND via 14 and the GND via 9b. The distance between the return current flowing along the GND vias 14 and 9b is short, and the return current easily flows through the GND vias 14 and 9b. Therefore, a phenomenon in which a part of the energy of the return current is radiated to the space hardly occurs. Further, unlike the invention described in Patent Document 1, there is no possibility that a stub is generated in the vicinity of the ridge line portion 2d (FIG. 2A) of the base material 2.
Therefore, according to the high-frequency transmission line substrate 1a having such a structure, it is possible to reduce transmission loss in the conversion unit 8 of the microstrip line 6 and the grounded coplanar line 7.

The transmission characteristic in the conversion part of the high-frequency transmission line substrate of the present invention will be described using a numerical analysis result of the transmission coefficient S21, which is one of the elements (S parameters) of the scattering matrix (S matrix), in comparison with the prior art. To do.
5 (a) and 5 (b) are plan views of the main part of the high-frequency transmission line substrate according to the prior art. FIGS. 6 and 7 show the results obtained by numerical analysis of the transmission characteristics (transmission coefficient S21) of the high-frequency transmission line substrate of the prior art and this example, respectively. The components shown in FIGS. 1 to 4 are denoted by the same reference numerals, and the description thereof is omitted.

As shown in FIGS. 5A and 5B, the high-frequency transmission line substrate 50 of the prior art is the same as the GND via 9b, via land 12 in the high-frequency transmission line substrate 1a (FIG. 2A) of the present embodiment. In addition, there is no connection line 13 and the outline of the ground conductor 4a is formed in a substantially rectangular shape except for the vicinity of the conversion portion 8, and the conventional high-frequency transmission line substrate 51b is a modification of the present embodiment. equally a high-frequency transmission line substrate 1b (FIG. 3 (b)) connecting lines 13 width _{D 3} is the diameter _{D 4} of the arcuate outline of the via land 12 in the (FIG. 2 (a)) is an example, GND vias 9b The outer land line of the via land 12 is formed in a rectangular shape. In the following numerical analysis, the widths of the strip line 3a and the central conductor 3b in the high-frequency transmission line substrates 50, 51a, 51b are 0.25 mm and 0.1 mm, respectively, and the lengths are 1.3 mm and 1.5 mm, respectively. It was. Further, the distance _{W 1} between the ground conductor 4a and the center conductor 3b and 0.055 mm, and respectively 0.125mm and 0.1mm width _{D 2} of the width _{D 1} and via land 12 of the ground conductor 4a. The thickness of the strip line 3a, the central conductor 3b, the ground conductor 4a and the via land 12 is 55 μm, and the base material 2 is an alumina substrate having a relative dielectric constant of 9.0 (length 3 mm × width 6 mm × thickness 0. 3 mm). In addition, about the GND via | veer 9a, 9b, the diameter was set to 0.2 mm and the three-dimensional shape was modeled and included in the analysis conditions.

  6 and 7, the vertical axis represents the calculated value of the transmission coefficient S21, and the horizontal axis represents the frequency (GHz) of the transmitted signal. The solid line and the broken line in FIG. 6A represent the transmission coefficient S21 (calculated value) of the high-frequency transmission line substrate 50, 51a, respectively. The solid line and the broken line in FIG. The transmission coefficient S21 (calculated value) of 51b is represented. Further, the solid line and the broken line in FIG. 7A represent the transmission coefficient S21 (calculated value) of the high-frequency transmission line substrate 51a and 1a, respectively, and the solid line and the broken line in FIG. It represents the transmission coefficient S21 (calculated value) of 1b.

As shown in FIG. 6, the transmission coefficient S21 of the high-frequency transmission line substrates 51a and 51b exceeds the transmission coefficient S21 of the high-frequency transmission line substrate 50 over almost the entire frequency band. This is because part of the return current that did not flow to the GND via 14 in the high-frequency transmission line substrates 51a and 51b flows to the GND via 9b via the ground conductor 4b, so that the transmission loss in the conversion unit 8 is high-frequency transmission. It is shown that it is suppressed as compared with the line substrate 50.
On the other hand, in FIG. 7, the transmission coefficient S21 of the high-frequency transmission line substrates 1a and 1b exceeds the transmission coefficient S21 of the high-frequency transmission line substrates 51a and 51b in the frequency band of 45 GHz or higher. This is because, in the high-frequency transmission line substrates 1a and 1b, the distance between the return current flowing along the via land 12 and the edge of the connection line 13 and the GND vias 14 and 9b is short even between the GND via 14 and the GND via 9b. Compared with the case of the high-frequency transmission line substrates 51a and 51b, since the return current easily flows to the GND vias 14 and 9b, the phenomenon that part of the energy of the return current is radiated to the space is less likely to occur. 8 shows that the transmission loss is small.

In the present embodiment, the GND vias 9a and 9b are arranged so that the arrangement lines 11a and 11b are orthogonal to each other, but the angle α formed by the arrangement lines 11a and 11b is not necessarily 90 degrees. However, the GND vias 9a and 9b are preferably arranged so that the angle α is within a range of 90 ° ± 30 °. Further, the width D ₃ of the connection line 13 is not limited to the case shown in this embodiment can be appropriately changed. In order to effect the above-described via lands 12 are exerted, the width D ₃ of the connection line 13 is narrower the better as compared to the diameter D ₄ of the arcuate outline of the via land 12, the width D of the connection lines 13 _{If 3} is too narrow, the original function of the connection line 13 for conducting the via lands 12 to each other is not exhibited. Therefore, it is desirable that the width D ₃ of the connection line 13 is about twice the width D ₂ of the via land 12.
Further, the dimensions of the microstrip line 6, the grounded coplanar line 7, and the ground conductors 4a and 4b and the material of the substrate 2 are not limited to those shown in the present embodiment, and can be changed as appropriate.

  The invention described in claim 1 and claim 2 can be applied to various transmission line substrates having a microstrip line and a grounded coplanar line.

  DESCRIPTION OF SYMBOLS 1a, 1b ... High-frequency transmission line board | substrate 2 ... Base material 2a ... Front surface 2b ... Back surface 2c ... Through-hole 2d ... Edge line part 3 ... Signal line conductor 3a ... Strip conductor 3b ... Center conductor 4a, 4b ... Ground conductor 5 ... Ground layer DESCRIPTION OF SYMBOLS 6 ... Microstrip line 7 ... Grounded coplanar line 8 ... Conversion part 9a, 9b ... GND via 10 ... Metal conductor 11a, 11b ... Arrangement line 12 ... Via land 13 ... Connection line 14 ... GND via 50 ... Transmission line substrate for high frequency 51a, 51b ... high-frequency transmission line substrate

Claims (2)

A first signal line conductor formed on one surface of a base material made of a dielectric, a pair of first ground conductors provided symmetrically across the first signal line conductor, and the first A second ground conductor extending from the pair of first ground conductors in a direction away from the signal line conductor, a ground layer formed on the other surface of the substrate, and the ground layer and the first A grounded coplanar line having a plurality of first vias and second vias that respectively conduct one ground conductor and the second ground conductor;
A microstrip line having a second signal line conductor connected to the first signal line conductor via a converter, and the ground layer;
With
The first ground conductor is provided along the first signal line conductor,
The second ground conductor has an arcuate outline and a via land formed so as to surround the first via closest to the conversion unit and the opening of the second via with a predetermined width. , Consisting of a connection line that makes this via land conductive,
The connection line is formed to have a width narrower than the diameter of the outer line of the via land.   2. The high-frequency transmission line substrate according to claim 1, wherein the width of the connection line is twice the width of the via land.

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