Transmission line

Abstract

A transmission line (1) includes: a first transmission line including a signal line conductor (11); a second transmission line including a signal line conductor (21) formed in a layer different from the signal line conductor (11); and a connection part (30) including a signal line narrow section (31) that is connected to an end (E12) of the signal line conductor (11) and is narrower than each of the signal line conductor (11) and the signal line conductor (21), and a connection via (33) that interlayer connects the signal line conductor (11) and the signal line conductor (21) via the signal line narrow section (31). The first transmission line is a microstrip line that includes the signal line conductor (11) and a ground conductor (12), and the second transmission line is a coplanar line that includes the signal line conductor (21) and ground conductors (22a, 22b) formed so as to sandwich the signal line conductor (21).

Description

transmission lines

[0001] This application claims priority to Japanese Patent Application No. 2024-047833, filed on March 25, 2024, the contents of which are incorporated herein by reference.

[0002] In recent years, wireless communications using high-frequency signals such as microwaves, quasi-millimeter waves, and millimeter waves have been attracting attention. For example, in 5G (fifth-generation mobile communications systems), high-frequency signals such as those in the 28 GHz band are used to achieve ultra-high speeds, ultra-low latency, and multiple simultaneous connections. Representative planar high-frequency transmission lines for transmitting such high-frequency signals include microstrip lines and coplanar lines. A microstrip line is generally a line in which a ground conductor is formed on one side of a dielectric and a signal line conductor is formed on the other side. A coplanar line is a line in which a ground conductor and a signal line conductor are formed on the same plane (e.g., on one side of a dielectric). In both microstrip lines and coplanar lines, high-frequency signals are transmitted via two conductors (a signal line conductor and a ground conductor).

[0003] The following Patent Documents 1 and 2 disclose a transmission line in which a coplanar waveguide signal conductor is formed on the same plane as a ground conductor of a microstrip line, and the microstrip line signal conductor and the coplanar waveguide signal conductor are connected to each other via an interlayer connection. Specifically, an open end of the microstrip line signal conductor is connected to an open end of the coplanar waveguide signal conductor via a through hole, thereby achieving an interlayer connection between the microstrip line signal conductor and the coplanar waveguide signal conductor.

[0004] Japanese Unexamined Patent Publication No. 2005-94445 Japanese Unexamined Patent Publication No. 5-199019

[0005] In the transmission lines disclosed in the above-mentioned Patent Documents 1 and 2, the width of the signal line conductor of the microstrip line is generally significantly different from the width of the signal line conductor of the coplanar line. For example, the width of the signal line conductor of the microstrip line is sometimes designed to be about five times the width of the signal line conductor of the coplanar line. In this transmission line in which a first transmission line (e.g., a microstrip line) and a second transmission line (e.g., a coplanar line) are interlayer-connected, a significant difference in the width of the signal line conductors of the first transmission line and the second transmission line may increase reflection loss.

[0006] The present disclosure has been made in consideration of the above circumstances, and aims to provide a transmission line that can reduce reflection loss when connecting a first transmission line and a second transmission line between layers.

[0007] In order to solve the above-mentioned problems, a transmission line (1) according to a first aspect of the present disclosure includes a first transmission line (10) having a first signal line conductor (11), a second transmission line (20) having a second signal line conductor (21) formed in a layer different from that of the first signal line conductor, and a signal line narrow portion (31, 37) connected to at least one of an end (E12) of the first signal line conductor and an end (E21) of the second signal line conductor and having a width narrower than that of the first signal line conductor and the second signal line conductor. and a connection portion (30) having a connection via (15, 33, 36) that electrically connects the first signal line conductor and the second signal line conductor between layers via the signal line narrow portion, wherein the first transmission line is a microstrip line having the first signal line conductor and a first ground conductor (12), and the second transmission line is a coplanar line having the second signal line conductor and two second ground conductors (22 a, 22 b) that are formed so as to sandwich the second signal line conductor.

[0008] In a transmission line according to a first aspect of the present disclosure, a first signal line conductor of a first transmission line and a second signal line conductor of a second transmission line are connected to each other by a connecting via through a signal line narrow portion that is narrower than the first signal line conductor and the second signal line conductor, thereby introducing an inductance component due to the signal line narrow portion, and thereby reducing reflection loss due to a capacitance component that occurs when the microstrip line and the coplanar line are connected to each other.

[0009] Furthermore, a transmission line according to a second aspect of the present disclosure is the transmission line according to the first aspect of the present disclosure, wherein the connection portion in the transmission line according to the first aspect of the present disclosure further includes two ground connection conductors (35 a, 35 b) connected to the first ground conductor and two second ground conductors, respectively, so as to surround the signal line narrow portion and the connection via in a planar view, and the first ground conductor, the second signal line conductor, the two second ground conductors, and the two ground connection conductors are formed on the same layer.

[0010] A transmission line according to a third aspect of the present disclosure is the transmission line according to the second aspect of the present disclosure, wherein the first transmission line includes two third ground conductors (13 a, 13 b) that are formed in the same layer as the first signal line conductor so as to sandwich the first signal line conductor and are connected to the first ground conductor through vias (14), and the width of the ground connection conductor is narrower than the width of either the second ground conductor or the third ground conductor.

[0011] Furthermore, in a transmission line according to a fourth aspect of the present disclosure, in the transmission line according to the third aspect of the present disclosure, the width of the ground connection conductor is narrower than half the narrower of the width of the second ground conductor and the width of the third ground conductor.

[0012] Furthermore, a transmission line according to a fifth aspect of the present disclosure is the transmission line according to the second to fourth aspects of the present disclosure, wherein the two ground connection conductors extend so as to protrude beyond one side edge of the first ground conductor and one side edge of the two second ground conductors in a direction intersecting the direction in which the first transmission line and the second transmission line extend, and protrude beyond the other side edge of the first ground conductor and the other side edges of the two second ground conductors.

[0013] Furthermore, a transmission line according to a sixth aspect of the present disclosure is the transmission line according to any one of the first to fifth aspects of the present disclosure, but has a shape that is bent in a direction that intersects with the direction in which the first transmission line and the second transmission line extend.

[0014] Furthermore, a transmission line according to a seventh aspect of the present disclosure is the transmission line according to any one of the first to sixth aspects of the present disclosure, wherein the second transmission line includes a fourth ground conductor (23) formed in a layer different from the layer in which the second signal line conductor and the second ground conductor are formed and connected to the second ground conductor through a via (24).

[0015] Furthermore, in the transmission line according to an eighth aspect of the present disclosure, in the transmission line according to the first to seventh aspects of the present disclosure, the signal line narrow portion (31) connected to the end (E12) of the first signal line conductor is formed in a layer different from the layer in which the first signal line conductor is formed, and is electrically connected to the first signal line conductor through the connection via.

[0016] Furthermore, in the transmission line according to a ninth aspect of the present disclosure, in the transmission line according to the first to eighth aspects of the present disclosure, the signal line narrow portion (37) connected to the end (E21) of the second signal line conductor is formed in a layer different from the layer in which the second signal line conductor is formed, and is electrically connected to the second signal line conductor through the connection via.

[0017] According to the present disclosure, it is possible to reduce reflection loss when connecting a first transmission line and a second transmission line between layers.

[0018] FIG. 1 is a perspective view showing a configuration of a main part of a transmission line according to an embodiment of the present disclosure; FIG. 2 is an enlarged perspective view of a portion of a transmission line according to an embodiment of the present disclosure; FIG. 3 is an enlarged plan view of a portion of a transmission line according to an embodiment of the present disclosure; FIG. 4 is a plan view showing a portion of a transmission line according to a first modified example; FIG. 5 is a plan view showing a portion of a transmission line according to a second modified example; FIG. 6 is a side view showing a portion of a transmission line according to a third modified example; FIG. 7 is a perspective view showing a configuration of a main part of a transmission line according to a fourth modified example; FIG. 8 is a perspective view showing a configuration of a main part of a transmission line according to a fifth modified example; FIG. 9 is a diagram showing the reflection characteristics of a transmission line according to an embodiment of the present disclosure and a transmission line according to a comparative example;

[0019] Hereinafter, transmission lines according to embodiments of the present disclosure will be described in detail with reference to the drawings. For ease of understanding, the positional relationships of the components will be described with reference to an XYZ Cartesian coordinate system (the position of the origin will be changed as appropriate) set in the drawings as needed.

[0020] FIG. 1 is a perspective view showing a main configuration of a transmission line according to an embodiment of the present disclosure. As shown in FIG. 1 , the transmission line 1 of this embodiment includes a microstrip line 10 (first transmission line), a coplanar line 20 (second transmission line), and a connection portion 30 that provides interlayer connection between the microstrip line 10 and the coplanar line 20. Such a transmission line 1 is a line with a multilayer structure formed using semiconductor manufacturing technology. The transmission line 1 illustrated in FIG. 1 has a four-layer structure. Hereinafter, for ease of understanding, the four layers arranged in order from the −Z side to the +Z side are referred to as the “first layer,” “second layer,” “third layer,” and “fourth layer.” A view of the transmission line 1 viewed in the Z direction is referred to as a “plan view.”

[0021] 1 is a line that transmits high-frequency signals such as microwaves, quasi-millimeter waves, and millimeter waves. Specifically, when a high-frequency signal is input to port P1 of microstrip line 10, transmission line 1 transmits the input high-frequency signal sequentially through microstrip line 10 and coplanar line 20 and outputs it from port P2 of coplanar line 20. When a high-frequency signal is input to port P2 of coplanar line 20, transmission line 1 transmits the input high-frequency signal sequentially through coplanar line 20 and microstrip line 10 and outputs it from port P1 of microstrip line 10.

[0022] The microstrip line 10 includes a signal line conductor 11 (first signal line conductor), a ground conductor 12 (first ground conductor), and ground conductors 13a and 13b (third ground conductors). The signal line conductor 11 is a linear strip conductor that extends in the X direction and has a constant width, constant thickness, and a predetermined length. In a plan view, the size of the conductor in a direction perpendicular to the extension direction of the conductor is referred to as the width. The size of the conductor in a direction perpendicular to both the extension direction and the width direction of the conductor is referred to as the thickness. One end E11 of the signal line conductor 11 serves as a port P1 through which a high-frequency signal is input or output, and the other end E12 (end) is connected to the coplanar line 20 via a connection portion 30. The signal line conductor 11 is formed on the fourth layer. The end on the −X side of the conductor is sometimes referred to as the “one end,” and the end on the +X side is sometimes referred to as the “other end.”

[0023] The ground conductor 12 is a strip-shaped conductor extending in the X direction, having a width wider than that of the signal line conductor 11, a constant thickness, and approximately the same length as that of the signal line conductor 11. The ground conductor 12 is formed on the third layer. The ground conductors 13a and 13b are linear strip-shaped conductors extending in the X direction, having a width narrower than that of the signal line conductor 11, a constant thickness, and approximately the same length as that of the signal line conductor 11. The ground conductors 13a and 13b are formed on the fourth layer so as to sandwich the signal line conductor 11 in the Y direction with a predetermined gap between them. The ground conductors 13a and 13b are connected to the ground conductor 12 through multiple vias 14 provided at multiple locations in the X direction.

[0024] The signal line conductor 11 is disposed so as to be located at the center of the ground conductor 12 in the Y direction. The ground conductor 13a is disposed so that one side edge (+Y side) thereof is positioned substantially in the Y direction as one side edge (+Y side) of the ground conductor 12, and the ground conductor 13b is disposed so that the other side edge (-Y side) thereof is positioned substantially in the Y direction as the other side edge (-Y side) of the ground conductor 12. Furthermore, the signal line conductor 11, the ground conductor 12, and the ground conductors 13a and 13b are disposed so that the ends on the -X side and the ends on the +X side are positioned substantially in the X direction.

[0025] The coplanar line 20 includes a signal line conductor 21 (second signal line conductor), ground conductors 22a and 22b (second ground conductors), and a ground conductor 23 (fourth ground conductor). The signal line conductor 21 is a linear strip conductor that extends in the X direction and has a constant width, a constant thickness, and a predetermined length. The width of the signal line conductor 21 is smaller than the width of the signal line conductor 11 of the microstrip line 10. For example, the width of the signal line conductor 21 is approximately one-third the width of the signal line conductor 11. One end E21 (end) of the signal line conductor 21 is connected to the microstrip line 10 via a connection portion 30, and the other end E22 serves as a port P2 through which a high-frequency signal is input and output. The signal line conductor 21 is formed on the third layer.

[0026] The ground conductors 22a and 22b are linear strip conductors extending in the X direction, having a width and thickness approximately equal to that of the signal line conductor 21, and a length approximately equal to that of the signal line conductor 21. The ground conductors 22a and 22b are formed on the third layer so as to sandwich the signal line conductor 21 in the Y direction with a predetermined gap between them. The gap in the Y direction between the ground conductors 22a and 22b and the signal line conductor 21 is narrower than the gap in the Y direction between the signal line conductor 11 and the ground conductors 13a and 13b in the microstrip line 10. For example, the gap in the Y direction between the ground conductors 22a and 22b and the signal line conductor 21 is approximately one-third of the gap in the Y direction between the signal line conductor 11 and the ground conductors 13a and 13b.

[0027] The ground conductors 22a and 22b are connected to the ground conductor 23 through a plurality of vias 24 provided at a plurality of locations in the X direction. The ground conductor 23 is a strip-shaped conductor that extends in the X direction and has a width wider than that of the signal line conductor 21, a constant thickness, and approximately the same length as the ground conductors 22a and 22b. The ground conductor 23 is formed on the first layer.

[0028] Here, on the second layer between the third layer on which the ground conductors 22a and 22b are formed and the first layer on which the ground conductor 23 is formed, a plurality of relay pads 25 are formed at positions where the vias 24 are provided. The relay pads 25 are connected to the ground conductors 22a and 22b through the vias 24 on the +Z side, and are connected to the ground conductor 23 through the vias 24 on the −Z side. In other words, the ground conductors 22a and 22b and the ground conductor 23 are connected via the relay pads 25.

[0029] The reason for connecting the ground conductors 22a, 22b and the ground conductor 23 via the relay pads 25 in this manner is to ensure a sufficient distance in the Z direction between the ground conductors 22a, 22b and the ground conductor 23. Note that, to further ensure a sufficient distance in the Z direction between the ground conductors 22a, 22b and the ground conductor 23, one or more layers other than the second layer may be formed between the ground conductors 22a, 22b and the ground conductor 23.

[0030] The signal line conductor 21 is disposed so as to be located in the center in the Y direction of the ground conductor 23. The ground conductor 22a is disposed so that one side edge (+Y side) thereof is positioned substantially in the Y direction as one side edge (+Y side) of the ground conductor 23, and the ground conductor 22b is disposed so that the other side edge (-Y side) thereof is positioned substantially in the Y direction as the other side edge (-Y side) of the ground conductor 23.

[0031] The ground conductors 22a and 22b and the ground conductor 23 are arranged so that their ends on the -X side are positioned at approximately the same position in the X direction, but the -X side end of the signal line conductor 21 is positioned closer to the -X side than the -X side ends of the ground conductors 22a and 22b and the ground conductor 23. The signal line conductor 21, the ground conductors 22a and 22b, and the ground conductor 23 are arranged so that their ends on the +X side are positioned at approximately the same position in the X direction.

[0032] 2 is an enlarged perspective view of a portion of a transmission line according to an embodiment of the present disclosure, and FIG. 3 is an enlarged plan view of a portion of a transmission line according to an embodiment of the present disclosure. As shown in FIG. 2 and FIG. 3, the connection portion 30 includes a signal line narrow portion 31, an upper pad 32, a connection via 33, a lower pad 34, and ground connection conductors 35 a and 35 b.

[0033] The signal line narrow section 31 is narrower than the signal line conductor 11 of the microstrip line 10, has approximately the same thickness as the signal line conductor 11, and is a linear strip-shaped conductor extending in the X direction with a predetermined length. The signal line narrow section 31 is formed on the fourth layer. The signal line narrow section 31 is formed to extend in the +X direction from the other end E12 of the signal line conductor 11. If the signal line conductor 11 of the microstrip line 10 and the signal line narrow section 31 of the connection section 30 are considered to be a single signal line, this signal line can be said to be a line formed so that its width narrows in a step-like manner at the other end E12 of the signal line conductor 11. The signal line narrow section 31 is provided to reduce the reflection loss of the transmission line 1 by introducing an inductance component into the signal line of the transmission line 1.

[0034] The upper pad 32 is a flat conductor having a rectangular shape in a plan view and connected to the other end (+X side) of the signal line narrow portion 31. The long sides of the upper pad 32 extend in the Y direction, and the short sides of the upper pad 32 extend in the X direction. The upper pad 32 is formed on the fourth layer. The lower pad 34 is a flat conductor having a rectangular shape in a plan view and connected to one end E21 of the signal line conductor 21 of the coplanar line 20. The long sides of the lower pad 34 extend in the Y direction, and the short sides of the upper pad 32 extend in the X direction. The lower pad 34 is formed on the third layer. The upper pad 32 and the lower pad 34 are formed to overlap in a plan view.

[0035] The upper pad 32 is provided to connect the signal line narrow portion 31 and the signal line conductor 21 of the coplanar line 20 with a plurality of connection vias 33 via the lower pad 34. The upper pad 32 and the lower pad 34 may be formed so that their long sides extend in the X direction and their short sides extend in the Y direction. The upper pad 32 and the lower pad 34 may also be connected by only one connection via 33. If the signal line narrow portion 31 and the signal line conductor 21 of the coplanar line 20 are directly connected by the connection via 33, the upper pad 32 and the lower pad 34 may be omitted.

[0036] The connection via 33 interlayer connects the upper pad 32 formed on the fourth layer with the lower pad 34 formed on the third layer. Here, the signal line conductor 11 of the microstrip line 10 is connected to the signal line narrow portion 31, and the upper pad 32 is connected to the signal line narrow portion 31. The signal line conductor 21 of the coplanar line 20 is connected to the lower pad 34. The upper pad 32 and the lower pad 34 are connected by the connection via 33. Therefore, it can be said that the connection via 33 connects the signal line conductor 11 of the microstrip line 10 with the signal line conductor 21 of the coplanar line 20 via the upper pad 32, the signal line narrow portion 31, and the lower pad 34.

[0037] The ground connection conductor 35a connects the ground conductor 12 of the microstrip line 10 to the ground conductor 22a of the coplanar line 20. The ground connection conductor 35b connects the ground conductor 12 of the microstrip line 10 to the ground conductor 22b of the coplanar line 20. The ground connection conductors 35a and 35b are formed on the third layer.

[0038] Specifically, the ground connection conductor 35a is an L-shaped conductor that extends in the +X direction from the other end (+X side) on the +Y side of the other end (+X side) of the ground conductor 12, bends in the −Y direction at one end (−X side) of the ground conductor 22a in the Y direction, and is connected to one side edge (+Y side) of the one end (−X side) of the ground conductor 22a. The ground connection conductor 35b is an L-shaped conductor that extends in the +X direction from the other end (+X side) on the −Y side of the other end (+X side) of the ground conductor 12, bends in the +Y direction at one end (−X side) of the ground conductor 22b in the Y direction, and is connected to the other side edge (−Y side) of the one end (−X side) of the ground conductor 22b.

[0039] 3, the ground connection conductors 35a and 35b are formed in a plan view so as to surround the signal line narrow portion 31, the upper pad 32, the connection via 33, and the lower pad 34 (not shown in Fig. 3) together with the ground conductor 12 and the ground conductor 23. That is, in the connection portion 30, unlike the microstrip line 10 and the coplanar line 20, the signal line narrow portion 31, the upper pad 32, the connection via 33, and the lower pad 34 are configured so as not to overlap with the ground conductors in a plan view. The reason for this configuration is to increase the inductance component of the signal line narrow portion 31.

[0040] 3 , the width W3 of the ground connecting conductors 35a and 35b is narrower than the width W1 of the ground conductors 13a and 13b of the microstrip line 10 and the width W2 of the ground conductors 22a and 22b of the coplanar line 20. Here, the width W3 of the ground connecting conductors 35a and 35b is preferably narrower than half the narrower of the width W1 of the ground conductors 13a and 13b and the width W2 of the ground conductors 22a and 22b. The width W3 of the ground connecting conductors 35a and 35b is narrowed in order to reduce the reflection loss of the transmission line 1 by introducing an inductance component into the ground connecting conductors 35a and 35b, which serve as the return path of the transmission line 1.

[0041] As described above, the transmission line 1 of this embodiment includes the microstrip line 10 having the signal line conductor 11 formed on the fourth layer, and the coplanar line 20 having the signal line conductor 21 formed on the third layer. The signal line narrow portion 31, which is narrower than the signal line conductor 11 and the signal line conductor 21, is connected to the signal line conductor 11, and the signal line conductor 11 and the signal line conductor 21 are electrically connected to each other via the signal line narrow portion 31 by the connecting via 33. In this embodiment, the upper pad 32 connected to the signal line conductor 11 and the lower pad 34 connected to the signal line conductor 21 are connected to each other via the connecting via 33.

[0042] In this transmission line 1, an inductance component of the signal line narrow section 31 itself and an inductance component resulting from the step-like shape when the signal line conductor 11 and the signal line narrow section 31 are considered as a single signal line are introduced into the signal line of the transmission line 1. This makes it possible to reduce the return loss resulting from the capacitor component that occurs when the microstrip line 10 and the coplanar line 20 are connected to each other via an interlayer connection. Furthermore, although the return loss of the transmission line 1 is frequency-dependent due to the capacitor component of the transmission line 1, the frequency dependence of the return loss of the transmission line 1 can be suppressed by the inductance component introduced by the signal line narrow section 31.

[0043] In this embodiment, the signal line narrow portion 31 does not overlap the ground conductor in plan view at the connection portion 30 that connects the microstrip line 10 and the coplanar line 20. This increases the inductance component of the signal line narrow portion 31, further reduces the reflection loss due to the capacitor component that occurs when the microstrip line 10 and the coplanar line 20 are connected to each other between layers, and further reduces the frequency dependency.

[0044] Additionally, in this embodiment, the width W3 of the ground connecting conductors 35a and 35b that connect the ground conductor 12 of the microstrip line 10 and the ground conductors 22a and 22b of the coplanar line 20 is set narrower than the width W1 of the ground conductors 13a and 13b and the width W2 of the ground conductors 22a and 22b. This introduces an inductance component into the ground connecting conductors 35a and 35b, which serve as the return path for the transmission line 1, thereby further reducing the reflection loss of the transmission line 1 and further reducing the frequency dependency.

[0045] <Modifications> <First Modification> Figure 4 is a plan view showing a portion of a transmission line according to a first modification. The first modification includes two examples. In Figure 4, components corresponding to those shown in Figures 1 to 3 are denoted by the same reference numerals. The transmission line according to the first modification shown in Figure 4 has ground connection conductors 35a and 35b of the connection portion 30 with different shapes. The ground connection conductors 35a and 35b can have any shape as long as they surround the signal line narrow portion 31, the upper pad 32, the connection via 33, and the lower pad 34 together with the ground conductor 12 and the ground conductor 23 in plan view.

[0046] 4A, the ground connection conductor 35a extends to protrude further toward the +Y direction than one side edge (+Y direction) of the ground conductor 12 and one side edge (+Y direction) of the ground conductor 22a. The ground connection conductor 35b extends to protrude further toward the -Y direction than the other side edge (-Y direction) of the ground conductor 12 and the other side edge (-Y direction) of the ground conductor 22b. As a result, the area of ​​the region enclosed by the ground connection conductors 35a, 35b, together with the ground conductor 12 and the ground conductor 23, is larger in plan view than in the configurations shown in FIGS.

[0047] Specifically, the ground connection conductor 35a is a generally J-shaped conductor that extends in the +Y direction from one edge (+Y side) of the other end (+X side) of the ground conductor 12, bends in the +X direction at a predetermined distance, extends in the +X direction to one end (-X side) of the ground conductor 22a in the Y direction, bends in the -Y direction at a position where it extends in the +X direction, and is connected to one edge (+Y side) of the one end (-X side) of the ground conductor 22a. The ground connection conductor 35b is a generally J-shaped conductor that extends in the -Y direction from the other edge (-Y side) of the other end (+X side) of the ground conductor 12, bends in the +X direction at a predetermined distance, extends in the +X direction to one end (-X side) of the ground conductor 22b in the Y direction, bends in the +Y direction at a position where it extends in the +X direction, and is connected to the other edge (-Y side) of the one end (-X side) of the ground conductor 22b.

[0048] 4(b), the ground connection conductor 35a protrudes in the +Y direction beyond one side edge (+Y side) of the ground conductor 12 and one side edge (+Y side) of the ground conductor 22a, and partially extends in the +X direction. Furthermore, the ground connection conductor 35b protrudes in the -Y direction beyond the other side edge (-Y side) of the ground conductor 12 and the other side edge (-Y side) of the ground conductor 22b, and partially extends in the +X direction. As a result, the area of ​​the region enclosed by the ground connection conductors 35a, 35b, together with the ground conductor 12 and the ground conductor 23, is larger in plan view than in the example shown in FIG. 4(a).

[0049] Specifically, the ground connection conductor 35a extends in the +Y direction from one side edge (+Y side) of the other end (+X side) of the ground conductor 12, bends in the +X direction after a predetermined distance, and continues in the +X direction to a position on the +X side of one end (-X side) of the ground conductor 22a in the Y direction. Then, it bends in the -Y direction from that position, bends in the -X direction after a predetermined distance, bends in the -X direction again at a position extending in the -X direction to one end (-X side) of the ground conductor 22a in the Y direction, and is connected to one side edge (+Y side) of one end (-X side) of the ground conductor 22a.

[0050] The ground connection conductor 35b extends in the −Y direction from the other side edge (−Y side) of the other end (+X side) of the ground conductor 12, bends in the +X direction after a predetermined distance, and continues in the +X direction to a position on the +X side of one end (−X side) of the ground conductor 22b in the Y direction. Then, the ground connection conductor 35b bends in the +Y direction from that position, bends in the −X direction after a predetermined distance, bends in the −X direction again after extending in the −X direction to one end (−X side) of the ground conductor 22b in the Y direction, and is connected to the other side edge (−Y side) of one end (−X side) of the ground conductor 22b.

[0051] According to the first modification described above, the lengths of the ground connecting conductors 35a and 35b can be made longer than in the transmission line 1 according to the embodiment described with reference to Figures 1 to 3. This allows the magnitude of the inductance component of the ground connecting conductors 35a and 35b, which serve as the return path of the transmission line 1, to be increased.

[0052] <Second Modification> Fig. 5 is a plan view showing a portion of a transmission line according to a second modification. In Fig. 5, components corresponding to those shown in Figs. 1 to 3 are denoted by the same reference numerals. The transmission line according to the second modification shown in Fig. 5 has a modified signal line narrow portion 31. Although the signal line narrow portion 31 shown in Figs. 1 to 3 has a shape that extends linearly in the X direction, the shape may be any shape.

[0053] 5, the signal line conductor 11 bends in the +Y direction at a position extending a first distance in the +X direction from the other end E12, then bends in the +X direction at a position extending a second distance from that position. Then, the signal line conductor 11 bends in the -Y direction at a position extending a third distance from that position, then bends in the +X direction at a position extending a second distance from that position, and is connected to the upper pad 32. In other words, the signal line narrow section 31 has a shape that bends in the Y direction, which intersects with the X direction. It should be noted that the example shown in FIG. 5 is merely an example.

[0054] According to the second modification described above, the length of the signal line narrow section 31 can be made longer or the shape of the signal line narrow section 31 can be made half-looped, as compared with the transmission line 1 according to the embodiment described with reference to Figures 1 to 3. This makes it possible to increase the magnitude of the inductance component of the signal line narrow section 31 that forms part of the signal line of the transmission line 1.

[0055] <<Third Modification>> Fig. 6 is a side view showing a portion of a transmission line according to a third modification. In Fig. 6, components corresponding to those shown in Figs. 1 to 3 are denoted by the same reference numerals. Also, Fig. 6 shows only components necessary for explanation, and components not necessary for explanation are omitted. The transmission line according to the third modification shown in Fig. 6 has a signal line narrow portion 31 provided in a layer different from the layer on which the signal line conductor 11 is formed.

[0056] 6, the signal line narrow section 31 is formed on a layer (referred to as the "fifth layer") that is formed on the +Z side of the fourth layer on which the signal line conductor 11 is formed. As shown in Fig. 6, one end (-X side) of the signal line narrow section 31 is connected to the other end (+X side) of the signal line conductor 11 via a connection via 15, and the other end (+X side) of the signal line narrow section 31 is connected to the upper pad 32 via a connection via 36.

[0057] The signal line narrow section 31 does not necessarily have to be formed on the fifth layer immediately above the fourth layer on which the signal line conductor 11 is formed. For example, the signal line narrow section 31 may be formed on a layer (referred to as the "sixth layer") formed on the +Z side of the fifth layer. Alternatively, the signal line narrow section 31 may be formed on a layer (referred to as the "seventh layer") formed on the +Z side of the sixth layer. In other words, the signal line narrow section 31 may be connected to the signal line conductor 11 and the upper pad 32 via one layer or multiple layers.

[0058] According to the third modification described above, the signal line narrow section 31 is formed in a layer different from the fourth layer on which the signal line conductor 11 is formed. This makes it possible to add the inductance component of the connection via 15 connecting the signal line conductor 11 and the signal line narrow section 31, and the inductance component of the connection via 36 connecting the signal line narrow section 31 and the upper pad 32, thereby making it possible to freely adjust the magnitude of the inductance component of the signal line narrow section 31.

[0059] <<Fourth Modification>> Fig. 7 is a perspective view showing the configuration of the main parts of a transmission line according to a fourth modification. In Fig. 7, components corresponding to those shown in Figs. 1 to 3 are denoted by the same reference numerals. In the transmission line according to the fourth modification shown in Fig. 7, the signal line narrow portion 31 of the connection portion 30 is omitted and a signal line narrow portion 37 is provided.

[0060] The narrow signal line portion 37 is a linear strip-shaped conductor that is narrower than the signal line conductor 21 of the coplanar line 20, has approximately the same thickness as the signal line conductor 21, and has a predetermined length extending in the X direction. The narrow signal line portion 37 is formed on the third layer. The narrow signal line portion 37 is formed to extend in the −X direction from one end E21 of the signal line conductor 21. If the signal line conductor 21 of the coplanar line 20 and the narrow signal line portion 37 of the connection portion 30 are considered to be a single signal line, then this signal line can be said to be a line formed so that its width narrows in a step-like manner at the end E21 of the signal line conductor 21. Like the narrow signal line portion 31, the narrow signal line portion 37 is provided to reduce the reflection loss of the transmission line 1 by introducing an inductance component into the signal line of the transmission line 1.

[0061] The upper pad 32 and the lower pad 34 are formed to overlap in plan view, similar to the transmission line 1 shown in Fig. 1, but are positioned on the -X side relative to their positions in the transmission line 1 shown in Fig. 1. The upper pad 32 is connected to the other end E12 (+X side) of the signal line conductor 11 of the microstrip line 10, and the lower pad 34 is connected to one end E21 (-X side) of the signal line narrow portion 37.

[0062] In this modification, the upper pad 32 and the lower pad 34 may also be formed so that their long sides extend in the X direction and their short sides extend in the Y direction. The upper pad 32 and the lower pad 34 may also be connected by only one connection via 33. When the signal line narrow portion 31 and the signal line conductor 11 of the microstrip line 10 are directly connected by the connection via 33, the upper pad 32 and the lower pad 34 may be omitted.

[0063] According to the fourth modification described above, the signal line narrow section 31 connected to the signal line conductor 11 of the microstrip line 10 is omitted, and instead a signal line narrow section 37 is provided connected to the signal line conductor 21 of the coplanar line 20. This increases the degree of freedom in designing the signal line narrow section in the connection section 30.

[0064] <Fifth Modification> Fig. 8 is a perspective view showing the configuration of the main parts of a transmission line according to a fifth modification. In Fig. 8, components corresponding to those shown in Figs. 1 to 3 and 7 are denoted by the same reference numerals. The transmission line according to the fifth modification shown in Fig. 8 has signal line narrow portions 31 and 37 at connection portion 30.

[0065] 1 and 7, the upper pad 32 and the lower pad 34 are formed to overlap in plan view, but are positioned such that their positions in the X direction are approximately midway between the other end E12 of the signal line conductor 11 and one end E21 of the signal line conductor 21. The upper pad 32 is connected to the other end (+X side) of the signal line narrow portion 31, as in the configuration shown in Fig. 1, and the lower pad 34 is connected to one end (-X side) of the signal line narrow portion 37, as in the configuration shown in Fig. 7.

[0066] In this modification, the upper pad 32 and the lower pad 34 may also be formed so that their long sides extend in the X direction and their short sides extend in the Y direction. The upper pad 32 and the lower pad 34 may also be connected by only one connection via 33. When the signal line narrow portion 31 and the signal line narrow portion 37 are directly connected by the connection via 33, the upper pad 32 and the lower pad 34 may be omitted.

[0067] According to the fifth modification described above, the signal line narrow section 37 is provided to connect to the signal line conductor 21 of the coplanar line 20, in addition to the signal line narrow section 31 connected to the signal line conductor 11 of the microstrip line 10. This increases the degree of freedom in designing the signal line narrow section in the connection section 30.

[0068] <Comparison between the embodiment and the comparative example> Fig. 9 is a perspective view showing the configuration of a main part of a transmission line according to the comparative example. A transmission line 100 according to the comparative example shown in Fig. 9 includes a microstrip line 10, a coplanar line 20, and a connection portion 40 that connects the microstrip line 10 and the coplanar line 20 between layers. The microstrip line 10 and the coplanar line 20 have the same configuration as the microstrip line 10 and the coplanar line 20 included in the transmission line 1 according to the embodiment of the present disclosure shown in Fig. 1. However, the signal line conductor 21 of the coplanar line 20 extends further in the -X direction than the transmission line 1 shown in Fig. 1.

[0069] The connection portion 40 includes an upper pad 41, a connection via 42, a lower pad 43, and ground connection conductors 44a and 44b. The upper pad 41 is connected to the other end (+X side) of the signal line conductor 11 of the microstrip line 10, and is a tapered flat conductor whose width gradually narrows toward the +X side. The upper pad 41 is formed on the fourth layer. Note that the transmission line 100 according to the comparative example does not have a configuration equivalent to the signal line narrow portion 31 shown in FIG. 1 .

[0070] The lower pad 43, like the lower pad 34 shown in FIG. 1 , is a rectangular flat conductor connected to one end (−X side) of the signal line conductor 21 of the coplanar line 20. The longer side of the lower pad 43 extends in the Y direction, and the shorter side of the lower pad 43 extends in the X direction. The lower pad 43 is formed on the third layer. The upper pad 41 and the lower pad 43 are formed so as to overlap in a plan view. The connection via 42 provides interlayer connection between the upper pad 41 formed on the fourth layer and the lower pad 43 formed on the third layer.

[0071] 1 , the ground connection conductor 44a connects the ground conductor 12 of the microstrip line 10 to the ground conductor 22a of the coplanar line 20. Similar to the ground connection conductor 35b shown in Fig. 1 , the ground connection conductor 44b connects the ground conductor 12 of the microstrip line 10 to the ground conductor 22b of the coplanar line 20. The ground connection conductors 35a and 35b are formed on the third layer.

[0072] The ground connection conductor 44a is an L-shaped conductor in a planar view, similar to the ground connection conductor 35a shown in Fig. 1, and the ground connection conductor 44b is an L-shaped conductor in a planar view, similar to the ground connection conductor 35b shown in Fig. 1. However, unlike the ground connection conductors 35a and 35b shown in Fig. 1, the ground connection conductors 44a and 44b are wider. Specifically, the widths of the ground connection conductors 44a and 44b are wider than the width W1 of the ground conductors 13a and 13b of the microstrip line 10 (see Fig. 3) and the width W2 of the ground conductors 22a and 22b of the coplanar line 20 (see Fig. 3).

[0073] As described above, the connection portion 40 of the transmission line 100 according to the comparative example differs significantly from the connection portion 30 of the transmission line 1 shown in Fig. 1 in the following two respects. The first difference is that the connection portion 40 does not have a configuration equivalent to the signal line narrow portion 31 shown in Fig. 1. The second difference is that the widths of the ground connection conductors 44a and 44b provided in the connection portion 40 are not narrowed as are the ground connection conductors 35a and 35b shown in Fig. 1.

[0074] 10 is a diagram showing the reflection characteristics of the transmission line according to the embodiment of the present disclosure and the transmission line according to the comparative example. As shown in Fig. 10, both the transmission line 1 according to the embodiment of the present disclosure and the transmission line 100 according to the comparative example have a characteristic in which the reflection coefficient increases (the return loss increases) as the frequency of the high-frequency signal increases.

[0075] 10, it can be seen that the transmission line 1 according to the embodiment of the present disclosure has a smaller reflection coefficient (return loss) in a frequency band of approximately 6 GHz or higher than the transmission line 100 according to the comparative example. Also, referring to Fig. 10, it can be seen that the transmission line 1 according to the embodiment of the present disclosure has a gentler slope of the graph showing the increase in reflection coefficient with increasing frequency than the transmission line 100 according to the comparative example, and that the frequency dependency of the return loss is suppressed.

[0076] The above describes a transmission line according to an embodiment of the present disclosure and a transmission line according to a modification thereof. However, the present disclosure is not limited to the above embodiment and modification, and modifications can be freely made within the scope of the present disclosure. For example, the above-described embodiments and modifications can be combined as appropriate. For example, the signal line narrow portion 37 of the transmission line according to the fifth modification shown in FIG. 7 can be shaped like the signal line narrow portion 31 of the transmission line according to the second modification shown in FIG. 5.

[0077] Furthermore, the signal line narrow section 37 of the transmission line according to the fifth modification shown in Fig. 7 can be provided in a layer different from the layer on which the signal line conductor 21 is formed, like the signal line narrow section 31 of the transmission line according to the third modification shown in Fig. 6. In this case, the signal line narrow section 37 provided in the layer different from the layer on which the signal line conductor 21 is formed is connected to the signal line conductor 21 and the lower pad 34 through vias (not shown) (vias corresponding to the connection vias 15 and 36 shown in Fig. 6).

[0078] In the above-described embodiment and modified examples, when the signal line conductor 11 of the microstrip line 10 and the signal line narrow portion 31 of the connection unit 30 are considered to be a single signal line, the shape of the signal line is such that the width narrows in a step-like manner at the other end E12 of the signal line conductor 11. Also, when the signal line conductor 21 of the coplanar line 20 and the signal line narrow portion 37 of the connection unit 30 are considered to be a single signal line, the shape of the signal line is such that the width narrows in a step-like manner at the one end E21 of the signal line conductor 21. However, the above-described signal line does not necessarily have to have a step-like narrowing shape, and may have, for example, a tapered shape in which the width gradually narrows.

[0079] In the above-described embodiment and modified examples, the microstrip line 10 includes the signal line conductor 11, the ground conductor 12, and the ground conductors 13 a and 13 b, but the ground conductors 13 a and 13 b may be omitted. In addition, by omitting the ground conductors 13 a and 13 b, the vias 14 connecting the ground conductors 13 a and 13 b to the ground conductor 12 may also be omitted.

[0080] In the above-described embodiment and modified example, the coplanar line 20 includes the signal line conductor 21, the ground conductors 22a and 22b, and the ground conductor 23. However, the ground conductor 23 may be omitted. In addition, the vias 24 and the relay pads 25 that connect the ground conductor 23 to the ground conductors 22a and 22b may also be omitted.

[0081] However, from the viewpoint of stabilizing the electric field distribution and reducing unwanted radiation, it is desirable to provide ground conductors 13 a and 13 b on the microstrip line 10. Furthermore, from the viewpoint of preventing the occurrence of unwanted modes, it is desirable to provide a ground conductor 23 on the coplanar line 20.

[0082] 1...transmission line, 10...microstrip line, 11...signal line conductor, 12...ground conductor, 13a, 13b...ground conductor, 14...via, 15...connection via, 20...coplanar line, 21...signal line conductor, 22a, 22b...ground conductor, 23...ground conductor, 24...via, 30...connection portion, 31...signal line narrow portion, 33...connection via, 35a, 35b...ground connection conductor, 36...connection via, 37...signal line narrow portion, E12...other end (end), E21...one end (end)

Claims

1. A transmission line comprising: a first transmission line having a first signal line conductor; a second transmission line having a second signal line conductor formed on a layer different from that of the first signal line conductor; and a connection portion having a signal line narrow portion connected to at least one of an end of the first signal line conductor and an end of the second signal line conductor and narrower than each of the first signal line conductor and the second signal line conductor, and a connection via for electrically connecting the first signal line conductor and the second signal line conductor between layers via the signal line narrow portion, wherein the first transmission line is a microstrip line having the first signal line conductor and a first ground conductor, and the second transmission line is a coplanar line having the second signal line conductor and two second ground conductors formed so as to sandwich the second signal line conductor.

2. The transmission line according to claim 1, wherein the connection portion further comprises two ground connection conductors connected to the first ground conductor and two second ground conductors, respectively, so as to surround the signal line narrow portion and the connection via in a plan view, and the first ground conductor, the second signal line conductor, the two second ground conductors, and the two ground connection conductors are formed on the same layer.

3. The transmission line according to claim 2, wherein the first transmission line includes two third ground conductors that are formed on the same layer as the first signal line conductor so as to sandwich the first signal line conductor and are connected to the first ground conductor through vias, and the width of the ground connection conductors is narrower than the widths of both the second ground conductor and the third ground conductor.

4. The transmission line according to claim 3, wherein the width of the ground connection conductor is narrower than half the narrower of the widths of the second ground conductor and the third ground conductor.

5. The transmission line according to any one of claims 2 to 4, wherein the two ground connection conductors extend so as to protrude beyond one side edge of the first ground conductor and one side edge of the two second ground conductors in a direction intersecting the direction in which the first transmission line and the second transmission line extend, and so as to protrude beyond the other side edge of the first ground conductor and the other side edges of the two second ground conductors.

6. A transmission line according to any one of claims 1 to 5, wherein the signal line narrow section has a shape that is bent in a direction that intersects with the direction in which the first transmission line and the second transmission line extend.

7. The transmission line according to any one of claims 1 to 6, wherein the second transmission line includes a fourth ground conductor that is formed on a layer different from the layer on which the second signal line conductor and the second ground conductor are formed and that is connected to the second ground conductor through a via.

8. A transmission line as claimed in any one of claims 1 to 7, wherein the signal line narrow section connected to the end of the first signal line conductor is formed in a layer different from the layer on which the first signal line conductor is formed, and is electrically connected to the first signal line conductor through the connection via.

9. A transmission line as claimed in any one of claims 1 to 8, wherein the signal line narrow section connected to the end of the second signal line conductor is formed in a layer different from the layer on which the second signal line conductor is formed, and is electrically connected to the second signal line conductor through the connection via.

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