High-frequency transmission line and electronic device

A high-frequency transmission line includes a laminate including dielectric layers, a first signal line provided on one of the dielectric layers, a second signal line crossing the first signal line when viewed in a plan view in a direction of lamination, the second signal line being positioned on the same dielectric layer as the first signal line except for a crossing portion that crosses with the first signal line, and an intermediate ground conductor provided between the first and second signal lines in the direction of lamination, so as to overlap with crossing portions of the first and second signal lines when viewed in a plan view in the direction of lamination.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to high-frequency transmission lines and electronic devices, more particularly to a high-frequency transmission line for use in high-frequency signal transmission and an electronic device including the same.

2. Description of Related Art

As inventions relevant to conventional high-frequency transmission lines, signal lines described in, for example, International Patent Publication WO 2011/007660 and Japanese Patent Laid-Open Publication No. 2011-71403 are known. Each of these signal lines includes a laminate, a signal line, and two ground conductors.

The laminate is formed by laminating a plurality of flexible insulator layers. The signal line is provided in the laminate. The signal line is positioned between the two ground conductors in the direction of lamination. Accordingly, the signal line and the two ground conductors form a stripline structure. The signal lines described in International Patent Publication WO 2011/007660 and Japanese Patent Laid-Open Publication No. 2011-71403 are formed by laminates, and therefore, are thinner than the diameter of a typical coaxial cable. Accordingly, they can be disposed in a narrow space within an electronic device.

Incidentally, in some cases, it is desired to cross two signal lines such as those described in International Patent Publication WO 2011/007660 and Japanese Patent Laid-Open Publication No. 2011-71403. However, crossing two signal lines results in two laminates overlapping at a crossing portion of the two signal lines, hence a significantly increased thickness at the crossing. On the other hand, it is conceivable to provide two signal lines in a single laminate, so as to cross each other within the laminate. This results in a reduced thickness at a crossing portion of two signal lines in a laminate, but crosstalk occurs between the signal lines because the signal lines are opposed to each other.

SUMMARY OF THE INVENTION

A high-frequency transmission line according to a preferred embodiment of the present invention includes a laminate including a plurality of dielectric layers, a first signal line provided on one of the dielectric layers, a second signal line crossing the first signal line when viewed in a plan view in a direction of lamination, the second signal line being positioned on the same dielectric layer as the first signal line except for a crossing portion that crosses with the first signal line, and an intermediate ground conductor provided between the first and second signal lines in the direction of lamination, so as to overlap with crossing portions of the first and second signal lines when viewed in a plan view in the direction of lamination.

An electronic device according to another preferred embodiment of the present invention includes a high-frequency transmission line and a housing accommodating the high-frequency transmission line. The high-frequency transmission line includes a laminate including a plurality of dielectric layers, a first signal line provided on one of the dielectric layers, a second signal line crossing the first signal line when viewed in a plan view in a direction of lamination, the second signal line being positioned on the same dielectric layer as the first signal line except for a crossing portion that crosses with the first signal line, and an intermediate ground conductor provided between the first and second signal lines in the direction of lamination, so as to overlap with crossing portions of the first and second signal lines when viewed in a plan view in the direction of lamination.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, a high-frequency transmission line according to various preferred embodiments of the present invention, along with an electronic device including the high-frequency transmission line, will be described with reference to the drawings.

The configuration of the high-frequency transmission line according to a preferred embodiment of the present invention will be described below with reference to the drawings.FIG. 1is an external oblique view of the high-frequency transmission line10according to the present preferred embodiment.FIG. 2is an exploded oblique view of a portion E1of the high-frequency transmission line10according to the present preferred embodiment.FIG. 3is an exploded oblique view of a portion E2of the high-frequency transmission line10according to the present preferred embodiment.FIG. 4is an exploded oblique view of a portion E3of the high-frequency transmission line10according to the present preferred embodiment.FIG. 5is an exploded oblique view of a connecting portion12gof the high-frequency transmission line10according to the present preferred embodiment.FIG. 6is an exploded oblique view of a connecting portion12iof the high-frequency transmission line10according to the present preferred embodiment.FIG. 7is a cross-sectional structure view of the portion E1of the high-frequency transmission line10according to the present preferred embodiment.FIG. 8is a cross-sectional structure view of the section E2of the high-frequency transmission line10according to the present preferred embodiment. In the following, the direction of lamination of the high-frequency transmission line10will be defined as a z-axis direction, for example. Moreover, the longitudinal direction of the high-frequency transmission line10will be defined as an x-axis direction, and the direction perpendicular to the x-axis and z-axis directions will be defined as a y-axis direction, for example.

The dielectric element assembly12includes line portions12ato12d, a crossing portion12e, and connecting portions12fto12i. The dielectric element assembly12is a flexible laminate preferably formed by laminating a protective layer14and dielectric sheets (dielectric layers)18ato18cin this order, from the positive side to the negative side in the z-axis direction, as shown inFIG. 2. In the following, the principal surface of the dielectric element assembly12that is located on the positive side in the z-axis direction will be referred to as a top surface, and the principal surface of the dielectric element assembly12that is located on the negative side in the z-axis direction will be referred to as a bottom surface.

The crossing portion12eis positioned near the center of the dielectric element assembly12both in the x-axis direction and in the y-axis direction. The line portion12aextends from the crossing portion12etoward the negative side in the x-axis direction. The line portion12bextends from the crossing portion12etoward the positive side in the x-axis direction. The line portion12cextends from the crossing portion12etoward the negative side in the y-axis direction, and bends to the negative side in the x-axis direction. The line portion12dextends from the crossing portion12etoward the positive side in the y-axis direction, and bends to the positive side in the x-axis direction.

The connecting portion12fpreferably has a rectangular or substantially rectangular shape connected to the end of the line portion12athat is located on the negative side in the x-axis direction. The connecting portion12gpreferably has a rectangular or substantially rectangular shape connected to the end of the line portion12bthat is located on the positive side in the x-axis direction. The connecting portion12hpreferably has a rectangular or substantially rectangular shape connected to the end of the line portion12cthat is located on the negative side in the x-axis direction. The connecting portion12ipreferably has a rectangular or substantially rectangular shape connected to the end of the line portion12dthat is located on the positive side in the x-axis direction.

The dielectric sheets18ato18c, when viewed in a plan view in the z-axis direction, preferably have the same shape as the dielectric element assembly12. The dielectric sheets18ato18care made of a flexible thermoplastic resin such as liquid crystal polymer or polyimide. The thickness D1of the dielectric sheet18ais equal or approximately equal to the thickness D2of the dielectric sheet18b, as shown inFIGS. 7 and 8. After lamination of the dielectric sheets18ato18c, the thicknesses D1and D2are, for example, about 50 μm to about 300 μm. In the present preferred embodiment, both of the thicknesses D1and D2preferably are about 150 μm, for example. In the following, the principal surface of each of the dielectric sheets18ato18cthat is located on the positive side in the z-axis direction will be referred to as a top surface, and the principal surface of each of the dielectric sheets18ato18cthat is located on the negative side in the z-axis direction will be referred to as a bottom surface.

The signal line20(first signal line) is a linear conductor provided in the dielectric element assembly12and consisting of line conductors20a,20b,20e,20f, and20g(the line conductor20fis not shown in the figures) and via-hole conductors b3and b4. The line conductors20aand20bextend in the x-axis direction along the top surfaces of the line portions18b-aand18b-b, respectively, as shown inFIGS. 2 and 4. The line conductor20eextends in the x-axis direction along the top surface of the crossing portion18c-e, as shown inFIG. 4. The line portions20fand20gextend in the x-axis direction along the top surfaces of the connecting portions18b-fand18b-g, respectively, as shown inFIG. 5(only the line portion20gis shown).

Furthermore, the via-hole conductor b3pierces through the line portion18b-ain the z-axis direction, as shown inFIG. 4, and connects the end of the line conductor20athat is located on the positive side in the x-axis direction to the end of the line conductor20ethat is located on the negative side in the x-axis direction. The via-hole conductor b4pierces through the line portion18b-bin the z-axis direction, as shown inFIG. 4, and connects the end of the line conductor20bthat is located on the negative side in the x-axis direction to the end of the line conductor20ethat is located on the positive side in the x-axis direction.

Furthermore, the line conductor20f(not shown) is connected to the end of the line conductor20athat is located on the negative side in the x-axis direction. The line conductor20gis connected to the end of the line conductor20bthat is located on the positive side in the x-axis direction, as shown inFIG. 5. Accordingly, the line conductors20fand20g, the via-hole conductor b3, the line conductor20e, the via-hole conductor b4, and the line conductors20band20gare connected in this order so as to define the signal line20. Note that the signal line20is positioned approximately at the center in the width direction of the dielectric sheets18. The signal line20as above preferably is made of a metal material mainly composed of silver or copper and having a low specific resistance, for example.

The signal line21(second signal line) is a linear conductor provided in the dielectric element assembly12and consisting of line conductors21c,21d,21e,21h, and21i(the line conductor21his not shown in the figures) and via-hole conductors b5and b6. The line conductor21cextends along the top surface of the line portion18b-c, as shown inFIG. 4, and more specifically, the line conductor21cextends toward the negative side in the y-axis direction, and bends to the negative side in the x-axis direction. The line conductor21dextends along the top surface of the line portion18b-d, as shown inFIG. 4, and more specifically, the line conductor21dextends toward the positive side in the y-axis direction, and bends to the positive side in the x-axis direction. The line conductor21eextends in the y-axis direction along the top surface of the crossing portion18a-e, as shown inFIG. 4. The line portions21hand21iextend in the x-axis direction along the top surfaces of the connecting portions18b-hand18b-i, respectively.

Furthermore, the via-hole conductor b5pierces through the line portion18a-cin the z-axis direction, as shown inFIG. 4, and connects the end of the line conductor21cthat is located on the positive side in the y-axis direction to the end of the line conductor21ethat is located on the negative side in the y-axis direction. The via-hole conductor b6pierces through the line portion18a-din the z-axis direction, as shown inFIG. 4, and connects the end of the line conductor21dthat is located on the negative side in the y-axis direction to the end of the line conductor21ethat is located on the positive side in the y-axis direction.

Furthermore, the line conductor21h(not shown) is connected to the end of the line conductor21cthat is located on the negative side in the x-axis direction. The line conductor21iis connected to the end of the line conductor21gthat is located on the positive side in the x-axis direction, as shown inFIG. 6. Accordingly, the line conductors21hand21c, the via-hole conductor b5, the line conductor21e, the via-hole conductor b6, and the line conductors21dand21iare connected in this order so as to define the signal line21. Note that the signal line21is positioned approximately at the center in the width direction of the dielectric sheets18. The signal line21as above preferably is made of a metal material mainly composed of silver or copper and having a low specific resistance, for example.

The signal lines20and21thus configured cross each other at the crossing portion12ewhen viewed in a plan view in the z-axis direction. In addition, the portion of the signal line20that crosses the signal line21(i.e., the line conductor20e) is positioned on the negative side in the z-axis direction relative to the portions of the signal line20that do not cross the signal line21(i.e., the line conductors20aand20band the connecting conductors20fand20g). Similarly, the portion of the signal line21that crosses the signal line20(i.e., the line conductor21e) is positioned on the positive side in the z-axis direction relative to the portions of the signal line21that do not cross the signal line20(i.e., the line conductors21cand21dand the connecting conductors21hand21i). That is, the signal lines20and21cross each other at positions farther away from each other in the z-axis direction than at positions where they do not cross each other.

The ground conductor22(first ground conductor) is provided in the dielectric element assembly12, more specifically, on the top surface of the dielectric sheet18a, as shown inFIGS. 2 through 6. Accordingly, the ground conductor22is positioned on the positive side in the z-axis direction relative to the portions where the signal lines20and21do not cross each other (i.e., the line conductors20a,20b,21c, and21dand the connecting conductors20f,20g,21h, and21i). The ground conductor22, when viewed in a plan view in the z-axis direction, preferably has the same or approximately the same shape as the dielectric element assembly12, and is made of a metal material mainly composed of silver or copper and having a low specific resistance, for example.

Furthermore, as shown inFIGS. 2 through 6, the ground conductor22includes main conductors22ato22d, a crossing conductor22e, and terminal conductors22fto22i(the terminal conductors22fand22hare not shown in the figures).

The main conductors22ato22dand the crossing conductor22eare positioned on the top surfaces of the line portions18a-ato18a-dand the crossing portion18a-e, respectively, so as to overlap with the line conductors20a,20b,21c, and21dof the signal lines20and21when viewed in a plan view in the z-axis direction. The main conductors22cand22dand the crossing conductor22ehave an opening Op1provided therein. The line conductor21eis positioned within the opening Op1. Accordingly, the main conductors22cand22dand the crossing conductor22eare not in contact with the line conductor21e. Moreover, there is no opening other than the opening Op1provided in the main conductors22ato22d. Accordingly, the main conductors22ato22dhave no opening that overlaps with the signal lines20and21. Note that the main conductors22ato22dare strip-shaped solid conductors extending along the line portions18a-ato18a-d, respectively, and connected at the crossing portion18a-e.

The terminal conductor22gis positioned on the top surface of the connecting portion18a-g, and is connected to the end of the main conductor22bthat is located on the positive side in the x-axis direction, as shown inFIG. 5. The terminal conductor22gis in the shape of a rectangular or substantially rectangular or substantially rectangular frame. The terminal conductor22fis positioned on the top surface of the connecting portion18a-f, and is connected to the end of the main conductor22athat is located on the negative side in the x-axis direction. The terminal conductor22fhas the same structure as the terminal conductor22g, and therefore, is not shown in the figure.

The terminal conductor22iis positioned on the top surface of the connecting portion18a-i, and is connected to the end of the main conductor22dthat is located on the positive side in the x-axis direction, as shown inFIG. 6. The terminal conductor22iis in the shape of a rectangular or substantially rectangular or substantially rectangular frame. The terminal conductor22his positioned on the top surface of the connecting portion18a-h, and is connected to the end of the main conductor22cthat is located on the negative side in the x-axis direction. The terminal conductor22hhas the same structure as the terminal conductor22i, and therefore, is not shown in the figure.

The ground conductor24(second ground conductor) is provided in the dielectric element assembly12, more specifically, on the top surface of the dielectric sheet18c, as shown inFIGS. 2 through 6. Accordingly, the ground conductor24is positioned on the negative side in the z-axis direction relative to the portions where the signal lines20and21do not cross each other (i.e., the line conductors20a,20b,21c, and21dand the connecting conductors20f,20g,21h, and21i). The ground conductor24, when viewed in a plan view in the z-axis direction, preferably has the same or approximately the same shape as the dielectric element assembly12, and is made of a metal material mainly composed of silver or copper and having a low specific resistance, for example.

Furthermore, as shown inFIGS. 2 through 6, the ground conductor24includes main conductors24ato24d, a crossing conductor24e, and terminal conductors24fto24i(the terminal conductors24fand24hare not shown in the figures).

The main conductors24ato24dand the crossing conductor24eare positioned on the top surfaces of the line portions18c-ato18c-dand the crossing portion18c-e, respectively, so as to overlap with the line conductors20a,20b,21c, and21dof the signal lines20and21when viewed in a plan view in the z-axis direction. The main conductors24aand24band the crossing conductor24ehave an opening Op2provided therein. The line conductor20eis positioned within the opening Op2. Accordingly, the main conductors24aand24band the crossing conductor24eare not in contact with the line conductor20e. Moreover, there is no opening other than the opening Op2provided in the main conductors24ato24d. Accordingly, the main conductors24ato24dhave no opening that overlaps with the signal lines20and21. Note that the main conductors24ato24dare strip-shaped solid conductors extending along the line portions18c-ato18c-d, respectively, and connected at the crossing portion18c-e.

The terminal conductor24gis positioned on the top surface of the connecting portion18c-g, and is connected to the end of the main conductor24bthat is located on the positive side in the x-axis direction, as shown inFIG. 5. The terminal conductor24gis in the shape of a rectangular or substantially rectangular frame. The terminal conductor24fis positioned on the top surface of the connecting portion18c-f, and is connected to the end of the main conductor24athat is located on the negative side in the x-axis direction. The terminal conductor24fhas the same structure as the terminal conductor24g, and therefore, is not shown in the figure.

The terminal conductor24iis positioned on the top surface of the connecting portion18c-i, and is connected to the end of the main conductor24dthat is located on the positive side in the x-axis direction, as shown inFIG. 6. The terminal conductor24iis in the shape of a rectangular or substantially rectangular frame. The terminal conductor24his positioned on the top surface of the connecting portion18c-h, and is connected to the end of the main conductor24cthat is located on the negative side in the x-axis direction. The terminal conductor24hhas the same structure as the terminal conductor24i, and therefore, is not shown in the figure.

In this manner, the line conductors20aand20bof the signal line20are sandwiched between the ground conductors22and24in the z-axis direction. Accordingly, the line conductors20aand20band the ground conductors22and24define a tri-plate stripline structure. Similarly, the line conductors21cand21dof the signal line21are sandwiched between the ground conductors22and24in the z-axis direction. Accordingly, the line conductors21cand21dand the ground conductors22and24define a tri-plate stripline structure.

The ground conductor26(intermediate ground conductor) is provided in the dielectric element assembly12, more specifically, on the top surface of the dielectric sheet18b, as shown inFIGS. 2 through 6. The ground conductor26, when viewed in a plan view in the z-axis direction, preferably has the same or approximately the same shape as the dielectric element assembly12, and is made of a metal material mainly composed of silver or copper and having a low specific resistance.

Furthermore, as shown inFIGS. 2 through 6, the ground conductor26includes main conductors26ato26d, a crossing conductor26e, and terminal conductors26fto26i(the terminal conductors26fand26hare not shown in the figures).

The main conductors26ato26dare pairs of linear conductors extending along the line portions18b-ato18b-d, respectively. More specifically, the main conductor26ais positioned on the top surface of the line portion18b-a, such that the pair of linear conductors are on opposite sides in the width direction of the line conductor20awhen viewed in a plan view in the z-axis direction. The main conductor26bis positioned on the top surface of the line portion18b-b, such that the pair of linear conductors are on opposite sides in the width direction of the line conductor20bwhen viewed in a plan view in the z-axis direction. That is, the line conductors20aand20bare sandwiched by the main conductors26aand26b, respectively, in the width direction. Moreover, the main conductor26cis positioned on the top surface of the line portion18b-c, such that the pair of linear conductors are on opposite sides in the width direction of the line conductor21cwhen viewed in a plan view in the z-axis direction. The main conductor26dis positioned on the top surface of the line portion18b-d, such that the pair of linear conductors are on opposite sides in the width direction of the line conductor21dwhen viewed in a plan view in the z-axis direction. That is, the line conductors21cand21dare sandwiched by the main conductors26cand26d, respectively, in the width direction.

The crossing conductor26eis positioned on the top surface of the crossing portion18b-e. Accordingly, the crossing conductor26eis positioned between the line conductors20eand21ein the z-axis direction, so as to overlap with the crossing portions of the line conductors20eand21ewhen viewed in a plan view in the z-axis direction. Moreover, the crossing conductor26eis connected to the main conductors26ato26d.

The terminal conductor26gis positioned on the top surface of the connecting portion18b-g, and is connected to the end of the main conductor26bthat is located on the positive side in the x-axis direction, as shown inFIG. 5. The terminal conductor26gis in the shape of a rectangular or substantially rectangular frame. The terminal conductor26fis positioned on the top surface of the connecting portion18b-f, and is connected to the end of the main conductor26athat is located on the negative side in the x-axis direction. The terminal conductor26fhas the same structure as the terminal conductor26g, and therefore, is not shown in the figure.

The terminal conductor26iis positioned on the top surface of the connecting portion18b-i, and is connected to the end of the main conductor26dthat is located on the positive side in the x-axis direction, as shown inFIG. 6. The terminal conductor26iis in the shape of a rectangular or substantially rectangular frame. The terminal conductor26his positioned on the top surface of the connecting portion18b-h, and is connected to the end of the main conductor26cthat is located on the negative side in the x-axis direction. The terminal conductor26hhas the same structure as the terminal conductor26i, and therefore, is not shown in the figure.

Here, the distance D1between the signal line20and the ground conductor22in the z-axis direction is equal or approximately equal to the distance D2between the signal line20and the ground conductor24in the z-axis direction, as shown inFIG. 7. The distance D1is equal or approximately equal to the thickness of the dielectric sheet18a, and the distance D2is equal or approximately equal to the thickness of the dielectric sheet18b.

Furthermore, the distance D1between the signal line21and the ground conductor22in the z-axis direction is equal or approximately equal to the distance D2between the signal line21and the ground conductor24in the z-axis direction, as shown inFIG. 8. The distance D1is equal or approximately equal to the thickness of the dielectric sheet18a, and the distance D2is equal or approximately equal to the thickness of the dielectric sheet18b.

The external terminal16bis a rectangular or substantially rectangular or substantially rectangular conductor provided on the top surface of the connecting portion18a-gand surrounded by the terminal conductor22g, as shown inFIG. 5. The external terminal16b, when viewed in a plan view in the z-axis direction, overlaps with the end of the line conductor20gthat is located on the positive side in the x-axis direction. The external terminal16bpreferably is made of a metal material mainly composed of silver or copper and having a low specific resistance, for example. In addition, the top surface of the external terminal16bpreferably is plated with gold, for example.

The external terminal16ais a rectangular or substantially rectangular or substantially rectangular conductor provided on the top surface of the connecting portion18a-fand surrounded by the terminal conductor22f. The external terminal16a, when viewed in a plan view in the z-axis direction, overlaps with the end of the line conductor20fthat is located on the negative side in the x-axis direction. The external terminal16ahas the same structure as the external terminal16b, and therefore, is not shown in the figure.

The external terminal16dis a rectangular or substantially rectangular conductor provided on the top surface of the connecting portion18a-iand surrounded by the terminal conductor22i, as shown inFIG. 6. The external terminal16d, when viewed in a plan view in the z-axis direction, overlaps with the end of the line conductor20ithat is located on the positive side in the x-axis direction. The external terminal16dpreferably is made of a metal material mainly composed of silver or copper and having a low specific resistance, for example. In addition, the top surface of the external terminal16dpreferably is plated with gold, for example.

The external terminal16cis a rectangular or substantially rectangular conductor provided on the top surface of the connecting portion18a-hand surrounded by the terminal conductor22h. The external terminal16c, when viewed in a plan view in the z-axis direction, overlaps with the end of the line conductor21hthat is located on the negative side in the x-axis direction. The external terminal16chas the same structure as the external terminal16d, and therefore, is not shown in the figure.

The via-hole conductor b1pierces through the connecting portion18a-gof the dielectric sheet18ain the z-axis direction. The via-hole conductor b1connects the external terminal16bto the end of the signal line20gthat is located on the positive side in the x-axis direction.

Note that the external terminal16a(not shown) and the end of the line conductor20fthat is located on the negative side in the x-axis direction are connected by a via-hole conductor. The via-hole conductor that connects the external terminal16a(not shown) and the end of the line conductor20fthat is located on the negative side in the x-axis direction is similar to the via-hole conductor b1, and therefore, is not shown in the figure.

The via-hole conductor b2pierces through the connecting portion18a-iof the dielectric sheet18ain the z-axis direction. The via-hole conductor b2connects the external terminal16dto the end of the line conductor21ithat is located on the positive side in the x-axis direction.

Note that the external terminal16c(not shown) and the end of the line conductor12hthat is located on the negative side in the x-axis direction are connected by a via-hole conductor. The via-hole conductor that connects the external terminal16c(not shown) and the end of the line conductor21hthat is located on the negative side in the x-axis direction is similar to the via-hole conductor b2, and therefore, is not shown in the figure.

The via-hole conductors B1pierce through the line portions18a-aand18a-bof the dielectric sheet18ain the z-axis direction, and, when viewed in a plan view in the z-axis direction, the via-hole conductors B1are positioned on the positive side in the y-axis direction relative to the signal line20, so as to be aligned in the x-axis direction. The via-hole conductors B2pierce through the line portions18b-aand18b-bof the dielectric sheet18bin the z-axis direction, and, when viewed in a plan view in the z-axis direction, the via-hole conductors B2are positioned on the positive side in the y-axis direction relative to the signal line20, so as to be aligned in the x-axis direction. The via-hole conductors B1and B2are connected to each other, such that each pair constitutes a single via-hole conductor. The end of the via-hole conductor B1that is located on the positive side in the z-axis direction is connected to the ground conductor22, and the end of the via-hole conductor B1that is located on the negative side in the z-axis direction is connected to the ground conductor26. Moreover, the end of the via-hole conductor B2that is located on the positive side in the z-axis direction is connected to the ground conductor26, and the end of the via-hole conductor B2that is located on the negative side in the z-axis direction is connected to the ground conductor24. As a result, the via-hole conductors B1and B2connect the ground conductors22,24, and26.

The via-hole conductors B3pierce through the line portions18a-aand18a-bof the dielectric sheet18ain the z-axis direction, and, when viewed in a plan view in the z-axis direction, the via-hole conductors B3are positioned on the negative side in the y-axis direction relative to the signal line20, so as to be aligned in the x-axis direction. The via-hole conductors B4pierce through the line portions18b-aand18b-bof the dielectric sheet18bin the z-axis direction, and, when viewed in a plan view in the z-axis direction, the via-hole conductors B4are positioned on the negative side in the y-axis direction relative to the signal line20, so as to be aligned in the x-axis direction. The via-hole conductors B3and B4are connected to each other, such that each pair constitutes a single via-hole conductor. The end of the via-hole conductor B3that is located on the positive side in the z-axis direction is connected to the ground conductor22, and the end of the via-hole conductor B3that is located on the negative side in the z-axis direction is connected to the ground conductor26. Moreover, the end of the via-hole conductor B4that is located on the positive side in the z-axis direction is connected to the ground conductor26, and the end of the via-hole conductor B4that is located on the negative side in the z-axis direction is connected to the ground conductor24. As a result, the via-hole conductors B3and B4connect the ground conductors22,24, and26.

The via-hole conductors B11pierce through the line portions18a-cand18a-dof the dielectric sheet18ain the z-axis direction, and, when viewed in a plan view in the z-axis direction, the via-hole conductors B11are positioned on the positive side in the y-axis direction relative to the signal line21, so as to be aligned in the x-axis direction. The via-hole conductors B12pierce through the line portions18b-cand18b-dof the dielectric sheet18bin the z-axis direction, and, when viewed in a plan view in the z-axis direction, the via-hole conductors B12are positioned on the positive side in the y-axis direction relative to the signal line21, so as to be aligned in the x-axis direction. The via-hole conductors B11and B12are connected to each other, such that each pair constitutes a single via-hole conductor. The end of the via-hole conductor B11that is located on the positive side in the z-axis direction is connected to the ground conductor22, and the end of the via-hole conductor B11that is located on the negative side in the z-axis direction is connected to the ground conductor26. Moreover, the end of the via-hole conductor B12that is located on the positive side in the z-axis direction is connected to the ground conductor26, and the end of the via-hole conductor B12that is located on the negative side in the z-axis direction is connected to the ground conductor24. As a result, the via-hole conductors B11and B12connect the ground conductors22,24, and26. Note that in the sections where the line portions12cand12dextend in the y-axis direction, the via-hole conductors B11and B12, when viewed in a plan view in the z-axis direction, are positioned on the negative side in the x-axis direction relative to the signal line21, as shown in FIG.4.

The via-hole conductors B13pierce through the line portions18a-cand18a-dof the dielectric sheet18ain the z-axis direction, and, when viewed in a plan view in the z-axis direction, the via-hole conductors B13are positioned on the negative side in the y-axis direction relative to the signal line21, so as to be aligned in the x-axis direction. The via-hole conductors B14pierce through the line portions18b-cand18b-dof the dielectric sheet18bin the z-axis direction, and, when viewed in a plan view in the z-axis direction, the via-hole conductors B14are positioned on the negative side in the y-axis direction relative to the signal line21, so as to be aligned in the x-axis direction. The via-hole conductors B13and B14are connected to each other, such that each pair constitutes a single via-hole conductor. The end of the via-hole conductor B13that is located on the positive side in the z-axis direction is connected to the ground conductor22, and the end of the via-hole conductor B13that is located on the negative side in the z-axis direction is connected to the ground conductor26. Moreover, the end of the via-hole conductor B14that is located on the positive side in the z-axis direction is connected to the ground conductor26, and the end of the via-hole conductor B14that is located on the negative side in the z-axis direction is connected to the ground conductor24. As a result, the via-hole conductors B13and B14connect the ground conductors22,24, and26. Note that in the sections where the line portions12cand12dextend in the y-axis direction, the via-hole conductors B13and B14, when viewed in a plan view in the z-axis direction, are positioned on the positive side in the x-axis direction relative to the signal line21, as shown inFIG. 4.

The via-hole conductors b1to b6, B1to B4, and B11to B14are preferably made of a metal material mainly composed of silver or copper and having a low specific resistance, for example. Note that through-holes with conductor layers including inner circumferential surfaces formed by plating or other suitable process may be used in place of the via-hole conductors b1to b6, B1to B4, and B11to B14.

The protective layer14covers the entire or substantially the entire top surface of the dielectric sheet18a. Accordingly, the ground conductor22is covered by the protective layer14. The protective layer14is made of, for example, a flexible resin such as a resist material.

Furthermore, as shown inFIGS. 2 through 6, the protective layer14includes line portions14ato14d, a crossing portion14e, and connecting portions14fto14i. The line portions14ato14dand the crossing portion14ecover the entire top surfaces of the line portions18a-a,18a-b,18a-c, and18a-dand the crossing portion18a-e, respectively, thus covering the main conductors22ato22d.

The connecting portion14gis connected to the end of the line portion14bthat is located on the positive side in the x-axis direction, so as to cover the top surface of the connecting portion18a-g, as shown inFIG. 5. The connecting portion14ghas rectangular or substantially rectangular openings Ha to Hd provided therein. The opening Ha is a rectangular or substantially rectangular opening positioned at the center of the connecting portion14g. The external terminal16bis exposed to the outside from the opening Ha. The opening Hb is a rectangular or substantially rectangular opening positioned on the positive side in the y-axis direction relative to the opening Ha. The opening Hc is a rectangular or substantially rectangular opening positioned on the positive side in the x-axis direction relative to the opening Ha. The opening Hd is a rectangular or substantially rectangular opening positioned on the negative side in the y-axis direction relative to the opening Ha. The terminal conductor22gis exposed to the outside from the openings Hb to Hd, so that the exposed portions serve as external terminals. Note that the connecting portion14fhas the same structure as the connecting portion14g, and therefore is not shown in the figure, and further, any description thereof will be omitted.

The connecting portion14iis connected to the end of the line portion14dthat is located on the positive side in the x-axis direction, so as to cover the top surface of the connecting portion18a-i. The connecting portion14ihas rectangular or substantially rectangular openings He to Hh provided therein. The opening He is a rectangular opening positioned at the center of the connecting portion14i. The external terminal16dis exposed to the outside from the opening He. The opening Hf is a rectangular or substantially rectangular opening positioned on the positive side in the y-axis direction relative to the opening He. The opening Hg is a rectangular or substantially rectangular opening positioned on the positive side in the x-axis direction relative to the opening He. The opening Hh is a rectangular or substantially rectangular opening positioned on the negative side in the y-axis direction relative to the opening He. The terminal portion22iis exposed to the outside from the openings Hf to Hh, so that the exposed portions serve as external terminals. Note that the connecting portion14hhas the same structure as the connecting portion14i, and therefore is not shown in the figure, and further, any description thereof will be omitted.

The connectors100aand100bare mounted on the top surfaces of the connecting portions12fand12g, respectively, and electrically connected to the signal line20and the ground conductors22,24, and26. The connectors100cand100dare mounted on the top surfaces of the connecting portions12hand12i, respectively, and electrically connected to the signal line21and the ground conductors22,24, and26. The connectors100ato100dare configured in the same manner, and therefore, only the configuration of the connector100bwill be described below by way of example.FIG. 9is an external oblique view of the connector100bin the high-frequency transmission line10.FIG. 10is a cross-sectional structure view of the connector100bin the high-frequency transmission line10.

The connector100bincludes a connector body102, external terminals104and106, a center conductor108, and an external conductor110, as shown inFIGS. 1, 9, and 10. The connector body102includes a rectangular or substantially rectangular plate and a cylindrical or substantially cylindrical portion coupled thereon, and is made of an insulating material such as resin.

The external terminal104is positioned on the plate of the connector body102on the negative side in the z-axis direction, so as to face the external terminal16b. The external terminal106is positioned on the plate of the connector body102on the negative side in the z-axis direction, so as to correspond to the parts of the terminal conductor22gthat are exposed from the openings Hb to Hd.

The center conductor108is positioned at the center of the cylindrical or substantially cylindrical portion of the connector body102, and is connected to the external terminal104. The center conductor108is a signal terminal to/from which a high-frequency signal is inputted/outputted. The external conductor110is positioned on the inner circumferential surface of the cylindrical portion of the connector body102, and is connected to the external terminal106. The external conductor110is a ground terminal to be kept at a ground potential.

The connector100bthus configured is mounted on the top surface of the connecting portion12g, such that the external terminal104is connected to the external terminal16b, and the external terminal106is connected to the terminal conductor22g, as shown inFIGS. 9 and 10. As a result, the signal line20is electrically connected to the center conductor108. In addition, the ground conductors22,24, and26are electrically connected to the external conductor110.

The high-frequency transmission line10preferably is used in a manner as will be described below.FIG. 11illustrates an electronic device200provided with the high-frequency transmission line10as viewed in a plan view in the y-axis direction.FIG. 12illustrates the electronic device200provided with the high-frequency transmission line10as viewed in a plan view in the z-axis direction.

The electronic device200includes the high-frequency transmission line10, circuit boards202aand202b, receptacles204ato204d(the receptacles204band204care not shown in the figures), a battery pack (metallic body)206, a housing210, and antennas212aand212b.

The housing210accommodates the high-frequency transmission line10, the circuit boards202aand202b, the receptacles204ato204d, the battery pack206, and the antennas212aand212b, as shown inFIGS. 11 and 12. The circuit board202aincludes, for example, a transmission or reception circuit provided thereon. The circuit board202bincludes, for example, a power circuit (a radio frequency integrated circuit: RFIC) provided thereon. The battery pack206is, for example, a lithium-ion secondary battery, and the surface thereof is wrapped by a metal cover. The circuit board202a, the battery pack206, and the circuit board202bare arranged in this order, from the negative side to the positive side in the x-axis direction.

The antenna212ais connected to the circuit board202aand is adapted to transmit/receive high-frequency signals in 800 MHz and 1800 MHz bands. The antenna212bis connected to the circuit board202aand is adapted to receive GPS signals.

The receptacle204ais provided on the principal surface of the circuit board202aon the negative side in the z-axis direction, and connected to the antenna212avia a wiring trace provided on the circuit board202a. The receptacle204ais connected to the connector100a. The receptacle204b(not shown) is provided on the principal surface of the circuit board202bon the negative side in the z-axis direction, and connected to the power circuit provided on the circuit board202b. The receptacle204bis connected to the connector100b. Accordingly, high-frequency signals transmitted/received by the antenna212aare transmitted to the signal line20.

The receptacle204c(not shown) is provided on the principal surface of the circuit board202aon the negative side in the z-axis direction, and connected to the antenna212bvia a wiring trace provided on the circuit board202a. The receptacle204cis connected to the connector100c. The receptacle204dis provided on the principal surface of the circuit board202bon the negative side in the z-axis direction, and connected to the power circuit provided on the circuit board202b. The receptacle204dis connected to the connector100d. Accordingly, high-frequency signals, which are GPS signals, transmitted/received by the antenna212bare transmitted to the signal line21.

Here, the top surface of the dielectric element assembly12(more precisely, the protective layer14) is in contact with the battery pack206. The dielectric element assembly12and the battery pack206are fixed by an adhesive or suchlike.

A non-limiting example of a method for producing the high-frequency transmission line10will be described below with reference toFIGS. 1 through 6. While the following description focuses on one high-frequency transmission line10as a non-limiting example, in actuality, large-sized dielectric sheets preferably are laminated and cut, so that a plurality of high-frequency transmission lines10are produced at the same time.

Prepared first are dielectric sheets18ato18cmade of a thermoplastic resin and having their entire top surfaces copper-foiled. The copper-foiled surfaces of the dielectric sheets18ato18care smoothened, for example, by galvanization for rust prevention. The thickness of the copper foil preferably is about 10 μm to about 20 μm, for example.

Next, external terminals16ato16d, a line conductor21e, and a ground conductor22are formed on the top surface of the dielectric sheet18aby photolithography. Specifically, resists are printed on the copper foil on the top surface of the dielectric sheet18ain the same shapes as the external terminals16ato16d, the line conductor21e, and the ground conductor22. Then, any portions of the copper foil that are not coated with the resists are removed by etching the copper foil. Thereafter, the resists are removed. In this manner, the external terminals16ato16d, the line conductor21e, and the ground conductor22are formed on the top surface of the dielectric sheet18a.

Next, line conductors20a,20b,20f,20g,21c,21d,21h, and21iand a ground conductor26are formed on the top surface of the dielectric sheet18bby photolithography. In addition, a line conductor20eand a ground conductor24are formed on the top surface of the dielectric sheet18cby photolithography. The line conductors20a,20b,20e,20f,20g,21c,21d,21h, and21iand the ground conductors24and26are formed in the same manner as the external terminals16ato16d, the line conductor21e, and the ground conductor22, and therefore, any descriptions about their formation steps will be omitted.

Next, via-holes are bored through the dielectric sheets18aand18bby irradiating their bottom surfaces with laser beams where via-hole conductors b1to b6, B1to B4, and B11to B14are to be formed. Thereafter, the via-holes provided in the dielectric sheets18aand18bare filled with a conductive paste.

Next, the dielectric sheets18ato18care stacked in this order, from the positive side to the negative side in the z-axis direction. Then, the dielectric sheets18ato18care heated and pressed from both the positive and negative sides in the z-axis direction, thus softening the dielectric sheets18ato18cso as to be bonded and integrated, while solidifying the conductive paste in the via-holes, so that the via-hole conductors b1to b6, B1to B4, and B11to B14are formed. Note that the via-hole conductors b1to b6, B1to B4, and B11to B14do not have to be obtained by filling via-holes completely with conductors, and may be obtained, for example, by forming conductors only along the inner circumferential surfaces of via-holes.

Next, a resin (resist) paste is applied to the top surface of the dielectric sheet18a, thereby forming a protective layer14.

The high-frequency transmission line10thus configured renders it possible to reduce the thickness of the dielectric element assembly12at crossing portions of the signal lines20and21. More specifically, in the high-frequency transmission line10, the portions of the signal line20that do not cross the signal line21(i.e., the line conductors20a,20b,20f, and20g) and the portions of the signal line21that do not cross the signal line20(i.e., the line conductors21c,21d,21h, and21i) are positioned on the same dielectric sheet18b. Moreover, the portion of the signal line20that crosses the signal line21(i.e., the line conductor20e) and the portion of the signal line21that crosses the signal line20(i.e., the line conductor21e) are positioned on the dielectric sheets18aand18c, respectively. That is, in the high-frequency transmission line10, only the portions of the signal lines20and21that cross each other are positioned on different dielectric sheets. This renders it possible to cross the signal lines20and21within one dielectric element assembly12. Thus, it is possible to eliminate the need to place two dielectric element assemblies on each other, so that the dielectric element assembly12is significantly reduced in thickness at the crossing portions of the signal lines20and21.

Furthermore, the high-frequency transmission line10renders it possible to significantly reduce or prevent crosstalk between the signal lines20and21. More specifically, the high-frequency transmission line10includes the ground conductor26provided between the signal lines20and21in the z-axis direction so as to overlap with the crossing portions of the signal lines20and21. The ground conductor26is kept at a ground potential. Accordingly, noise emitted from both of the signal lines20and21is absorbed into the ground conductor26. As a result, crosstalk between the signal lines20and21is significantly reduced or prevented.

Furthermore, in the high-frequency transmission line10, the line conductors20a,20b,20f,20g,21c, and21dare positioned on the same dielectric sheet18b. In addition, in the high-frequency transmission line10, the characteristic impedances of the line conductors20a,20b,20f,20g,21c, and21dare preferably set at a predetermined value (e.g., about 50Ω) because of the ground conductors22,24, and26. On the other hand, the characteristic impedance of the line conductor20eis preferably set at the predetermined value (e.g., about 50Ω) because of the ground conductors22eand26e, and the characteristic impedance of the line conductor21eis preferably set at the predetermined value (e.g., about 50Ω) because of the ground conductors24eand26e. As a result, the characteristic impedance among all of the line conductors is preferably set at the predetermined value (e.g., about 50Ω). Here, the line conductors20eand21edo not overlap with the ground conductors22and24in the z-axis direction. Accordingly, it is conceivable that the line conductors20eand21emight be coupled to metallic bodies, such as the battery pack206, or grounds of external circuits. However, most of the electric-field energy (lines of electric force) of the line conductor20eis coupled to the ground conductors22eand26e. Moreover, most of the electric-field energy (lines of electric force) of the line conductor21eis coupled to the ground conductors24eand26e. Accordingly, the characteristic impedance does not change significantly even if the battery pack206and the signal line20eare placed closer to each other. Thus, transmission loss is significantly reduced or prevented even if some portions of the high-frequency transmission line10are not covered by ground conductors.

First Modification

Hereinafter, a high-frequency transmission line10aaccording to a first modification of a preferred embodiment of the present invention will be described with reference to the drawings.FIG. 13is an exploded oblique view of a portion E1of the high-frequency transmission line10aaccording to the first modification.FIG. 14is an exploded oblique view of a portion E2of the high-frequency transmission line10aaccording to the first modification.FIG. 15is an exploded oblique view of a portion E3of the high-frequency transmission line10aaccording to the first modification.FIG. 16is a cross-sectional structure view of a section A1of the high-frequency transmission line10aaccording to the first modification.FIG. 17is a cross-sectional structure view of a section A2of the high-frequency transmission line10aaccording to the first modification.FIG. 18is a cross-sectional structure view of a section A3of the high-frequency transmission line10aaccording to the first modification.FIG. 19is a cross-sectional structure view of a section A4of the high-frequency transmission line10aaccording to the first modification. For an external oblique view of the high-frequency transmission line10a,FIG. 1will be referenced.

The high-frequency transmission line10adiffers from the high-frequency transmission line10in that openings30and31are provided in the ground conductor24, the signal lines20and21do not have uniform widths, and the ground conductor26is provided only in the crossing portion18b-e. The other features of the high-frequency transmission line10aare the same as the high-frequency transmission line10, and therefore, any descriptions thereof will be omitted.

The main conductors24aand24bof the ground conductor24include a plurality of openings30arranged along the signal line20, as shown inFIGS. 13 and 15. The opening30is shaped such that the dimension in the y-axis direction is greater at the center in the x-axis direction than at either end in the x-axis direction, as shown inFIG. 13. In the following, a section of the opening30that is located at the center in the x-axis direction will be referred to as a “section a1”, a section located on the positive side in the x-axis direction relative to the section a1will be referred to as a “section a2”, and a section located on the negative side in the x-axis direction relative to the section a1will be referred to as a “section a3”. The dimension of the opening30in the y-axis direction is greater in the section a1than both in the section a2and in the section a3. Accordingly, the opening30is cross-shaped, in the shape of a rectangle whose four corners have been cut away in the shape of smaller rectangles.

The openings30, when viewed in a plan view in the z-axis direction, overlap with the signal line20. Portions of the ground conductor24that are positioned between adjacent openings30will be referred to as “bridge portions60”. In this manner, the openings30and the bridge portions60are arranged so as to alternate with each other along the signal line20. Accordingly, the signal line20overlaps alternatingly with the openings30and the bridge portions60. The interval between adjacent bridge portions60is shorter than half the wavelength of a high-frequency signal to be transmitted through the signal line20.

Furthermore, in the high-frequency transmission line10a, a section where the signal line20overlaps with the opening30will be referred to as a “section A1”, and a section where the signal line20overlaps with the bridge portion60will be referred to as a “section A2”. The width W1of the signal line20in the section A1is greater than the width W2of the signal line20in the section A2, as shown inFIG. 13. More specifically, the width W1of the signal line20at the overlap with the opening30is greater than the width W2of the signal line20at the overlap with the bridge portion60.

As described above, no openings are provided in the main conductors22aand22b, and the openings30are provided in the main conductors24aand24b, so that the overlap of the ground conductor24with the signal line20is smaller in area than the overlap of the ground conductor22with the signal line20.

Furthermore, the main conductors24cand24dof the ground conductor24include a plurality of openings31arranged along the signal line21, as shown inFIGS. 14 and 15. The opening31is shaped such that the dimension in the y-axis direction is greater at the center in the x-axis direction than at either end in the x-axis direction, as shown inFIG. 14. In the following, a section of the opening31that is located at the center in the x-axis direction will be referred to as a “section a4”, a section located on the positive side in the x-axis direction relative to the section a4will be referred to as a “section a5”, and a section located on the negative side in the x-axis direction relative to the section a4will be referred to as a “section a6”. The dimension of the opening31in the y-axis direction is greater in the section a4than both in the section a5and in the section a6. Accordingly, the opening31is cross-shaped, in the shape of a rectangle whose four corners have been cut away in the shape of smaller rectangles.

The openings31, when viewed in a plan view in the z-axis direction, overlap with the signal line21. Portions of the ground conductor24that are positioned between adjacent openings31will be referred to as “bridge portions61”. In this manner, the openings31and the bridge portions61are arranged so as to alternate with each other along the signal line21. Accordingly, the signal line21overlaps alternatingly with the openings31and the bridge portions61. The interval between adjacent bridge portions61is shorter than half the wavelength of a high-frequency signal to be transmitted through the signal line21.

Furthermore, in the high-frequency transmission line10a, a section where the signal line21overlaps with the opening31will be referred to as a “section A3”, and a section where the signal line21overlaps with the bridge portion61will be referred to as a “section A4”. The width W1of the signal line21in the section A3is greater than the width W2of the signal line21in the section A4, as shown inFIG. 14. More specifically, the width W1of the signal line21at the overlap with the opening31is greater than the width W2of the signal line21at the overlap with the bridge portion61.

As described above, no openings are provided in the main conductors22cand22d, and the openings31are provided in the main conductors24cand24d, so that the overlap of the ground conductor24with the signal line21is smaller in area than the overlap of the ground conductor22with the signal line21.

In this manner, the characteristic impedances of the signal lines20and21in the high-frequency transmission line10aare mainly determined by the opposed areas of the signal lines20and21and the ground conductor22and the distances therebetween, as well as by the relative permittivities of the dielectric sheets18ato18c. Therefore, in the case where the characteristic impedance of each of the signal lines20and21is preferably set to about 50Ω, for example, the characteristic impedance of each of the signal lines20and21preferably is designed to become about 55Ω, slightly higher than about 50Ω, for example, because of the influence of the signal lines20and21and the ground conductor22. Moreover, the ground conductor24is shaped such that the characteristic impedance of each of the signal lines20and21becomes about 50Ω because of the influence of the signal lines20and21and the ground conductors22and24. In this manner, the ground conductor22plays the role of a reference ground conductor for the signal lines20and21.

On the other hand, the ground conductor24is a ground conductor that doubles as a shield for the signal lines20and21. Moreover, the ground conductor24is designed to make final adjustments such that the characteristic impedance of each of the signal lines20and21is preferably set to about 50Ω, as described above. More specifically, the sizes of the openings30and31, the widths of the bridge portions60and61, etc., are designed. In this manner, the ground conductor24plays the role of an auxiliary ground conductor for the signal lines20and21.

Furthermore, the distance D1between each of the signal lines20and21and the ground conductor22in the z-axis direction is greater than the distance D2between each of the signal lines20and21and the ground conductor24in the z-axis direction, as shown inFIGS. 16 through 19. The distance D1is equal or approximately equal to the thickness of the dielectric sheet18a, and the distance D2is equal or approximately equal to the thickness of the dielectric sheet18b.

In the high-frequency transmission line10athus configured, the characteristic impedance of the signal line20repeatedly fluctuates between two adjacent bridge portions60in such a manner as to increase in the order: minimum value Z3, intermediate value Z2, and maximum value Z1and thereafter, decrease in the order: maximum value Z1, intermediate value Z2, and minimum value Z3. More specifically, large capacitance is created between the signal line20and the ground conductor24in the section A2where the signal line20overlaps with the bridge portion60. Accordingly, in the section A2, capacitance (C) property is dominant in the characteristic impedance of the signal line20. Therefore, in the section A2, the characteristic impedance of the signal line20is at the minimum value Z3.

Furthermore, in the signal line20, the dimension of the opening30in the y-axis direction is at the maximum value in the section a1. As a result, small capacitance is created between the signal line20and the ground conductor24in the section a1. Accordingly, in the section a1, inductance (L) property is dominant in the characteristic impedance of the signal line20. Therefore, in the section a1, the characteristic impedance of the signal line20is at the maximum value Z1.

Furthermore, in the signal line20, the dimension of the opening30in the y-axis direction is less than the maximum value both in the section a2and in the section a3. As a result, in the sections a2and a3, medium capacitance is created between the signal line20and the ground conductor24. Accordingly, in the sections a2and a3, both inductance (L) and capacitance (C) properties are dominant in the characteristic impedance of the signal line20. Therefore, in the sections a2and a3, the characteristic impedance of the signal line20is at the intermediate value Z2.

Here, the sections between adjacent bridge portions60are arranged in the order: A2, a3, a1, a2, and A2, from the negative side to the positive side in the x-axis direction. Accordingly, the characteristic impedance of the signal line20fluctuates between adjacent bridge portions60in the order: minimum value Z3, intermediate value Z2, maximum value Z1, intermediate value Z2, and minimum value Z3. Moreover, the bridge portions60and the openings30alternatingly overlap along the signal line20. Therefore, the characteristic impedance of the signal line20increases and decreases cyclically. Note that the maximum value Z1preferably is, for example, about 70Ω, the intermediate value Z2preferably is, for example, about 55Ω, and the minimum value Z3preferably is, for example, about 30Ω. Further, the high-frequency transmission line10apreferably is designed such that the average characteristic impedance of the entire signal line20is about 50Ω, for example. Note that the characteristic impedance of the signal line21fluctuates in the same manner as the characteristic impedance of the signal line20.

As with the high-frequency transmission line10, the high-frequency transmission line10athus configured is significantly reduced in thickness of the dielectric element assembly12at the crossing portions of the signal lines20and21.

Further, as with the high-frequency transmission line10, the high-frequency transmission line10arenders it possible to significantly reduce or prevent crosstalk between the signal lines20and21.

Furthermore, the high-frequency transmission line10ais significantly thinner. More specifically, in the high-frequency transmission line10a, the signal line20, when viewed in a plan view in the z-axis direction, does not overlap with the ground conductor24in the section A1. Accordingly, little capacitance is created between the signal line20and the ground conductor24. Therefore, even if the distance between the signal line20and the ground conductor24in the z-axis direction is reduced, the capacitance created between the signal line20and the ground conductor24does not become excessively large. As a result, the characteristic impedance of the signal line20becomes less likely to deviate from a predetermined value (e.g., about 50Ω). Thus, it is possible to make the high-frequency transmission line10athinner while keeping the characteristic impedance of the signal line20at the predetermined value. Note that for the same reason, it is possible to make the high-frequency transmission line10athinner while keeping the characteristic impedance of the signal line21at the predetermined value. Reducing the thickness of the high-frequency transmission line10aallows the high-frequency transmission line10ato be bent more readily.

Furthermore, in the high-frequency transmission line10a, transmission loss in the signal line20is significantly reduced or prevented. More specifically, in the section A1, the signal line20overlaps with the opening30, so that little capacitance is created between the signal line20and the ground conductor24. Therefore, even if the width W1of the signal line20in the section A1is set greater than the width W2of the signal line20in the section A2, the characteristic impedance of the signal line20does not become excessively lower in the section A1than in the section A2. As a result, the high-frequency transmission line10arenders it possible to reduce the resistance of the signal line20while keeping the characteristic impedance of the signal line20at a predetermined value. Thus, the high-frequency transmission line10arenders it possible to reduce transmission loss in the signal line20. Note that for the same reason, transmission loss in the signal line21is significantly reduced or prevented as well.

Furthermore, the high-frequency transmission line10arenders it possible to significantly reduce or prevent the adverse effect of spurious radiation from the signal line20. More specifically, in the high-frequency transmission line10a, the openings30are arranged along the signal line20. Accordingly, the characteristic impedance of the signal line20is higher in the section A1where the signal line20overlaps with the opening30than in the section A2where the signal line20overlaps with the bridge portion60. Since the openings30and the bridge portions60alternatingly overlap with the signal line20, the characteristic impedance of the signal line20fluctuates cyclically. In such a case, a standing wave occurs between two adjacent sections A1, resulting in spurious radiation. Therefore, by setting the interval between adjacent openings30less than or equal to half the wavelength of a high-frequency signal to be used by the electronic device200, it is rendered possible to keep the frequency of spurious radiation from the signal line20outside the frequency band for high-frequency signals to be used by the electronic device200. Thus, the adverse effect of spurious radiation from the signal line20on the electronic device200is significantly reduced or prevented. Note that for the same reason, the adverse effect of spurious radiation from the signal line21on the electronic device200is significantly reduced or prevented as well.

Furthermore, in the high-frequency transmission line10a, the dimension of the opening30in the y-axis direction is greater in the section a1than both in the section a2and in the section a3. Accordingly, the distance between the signal line20and the ground conductor24is greater in the section a1than in the sections a2and a3. Moreover, the signal line20and the bridge portion60overlap with each other in the section A2. Accordingly, the distance between the signal line20and the ground conductor24is greater in the sections a2and a3than in the section A2. Therefore, in the section between adjacent bridge portions60, the distance between the signal line20and the ground conductor24increases gradually, and thereafter, decreases gradually, through the course from the negative side to the positive side in the x-axis direction.

Here, a magnetic field becomes more likely to be generated around the signal line20as the distance between the signal line20and the ground conductor24increases. Accordingly, in the section between adjacent bridge portions60, the magnetic field generated by the signal line20increases gradually, and thereafter, decreases gradually, through the course from the negative side to the positive side in the x-axis direction. As a result, the intensity of the magnetic field is prevented from changing sharply at the boundaries of the sections a1to a3and A2. Therefore, reflection of a high-frequency signal at the boundaries of the sections a1to a3and A2is significantly reduced, so that occurrence of a standing wave in the signal line20is prevented. Thus, in the high-frequency transmission line10a, spurious radiation from the signal line20is significantly reduced or prevented. Note that for the same reason, spurious radiation from the signal line21is significantly reduced or prevented as well.

Furthermore, in the high-frequency transmission line10a, the openings30are provided in the ground conductor24, so that the characteristic impedance of the signal line20fluctuates cyclically. Therefore, when the high-frequency transmission line10ais bent, the characteristic impedance of the signal line changes to a smaller degree compared to a high-frequency transmission line in which the characteristic impedance of a signal line is constant. Here, the high-frequency transmission line in which the characteristic impedance of a signal line is constant is intended to mean a high-frequency transmission line including, for example, either a solid ground conductor or aground conductor with a slit-shaped opening.

Furthermore, in the high-frequency transmission line10a, the openings31are provided in the ground conductor22, so that the characteristic impedance of the signal line21fluctuates cyclically. Therefore, when the high-frequency transmission line10ais bent, the characteristic impedance of the signal line changes to a smaller degree compared to a high-frequency transmission line in which the characteristic impedance of a signal line is constant.

Furthermore, the high-frequency transmission line10arenders it possible to prevent the characteristic impedance of each of the signal lines20and21from changing from a predetermined value. More specifically, the top surface of the dielectric element assembly12(more precisely, the protective layer14) is in contact with the battery pack206. In addition, the dielectric element assembly12and the battery pack206are fixed by an adhesive or other suitable material. Therefore, the ground conductor22in a solid form free of openings is positioned between the signal lines20and21and the battery pack206. As a result, capacitance is prevented from being created between each of the signal lines20and21and the battery pack206. Thus, the characteristic impedance of each of the signal lines20and21is prevented from changing from the predetermined value.

Second Modification

Hereinafter, a high-frequency transmission line10baccording to a second modification of a preferred embodiment of the present invention will be described with reference to the drawings.FIG. 20is an exploded oblique view of a portion E3of the high-frequency transmission line10baccording to the second modification. For an external oblique view of the high-frequency transmission line10b,FIG. 1will be referenced.

The high-frequency transmission line10bdiffers from the high-frequency transmission line10ain the following aspects. The first difference is that the high-frequency transmission line10bdoes not include the ground conductor26. The second difference is that the signal line21is positioned in its entirety on the dielectric sheet18b. The third difference is that a dielectric sheet18eis additionally provided, so that the line conductor20eis positioned on the top surface of the dielectric sheet18e. The fourth difference is that the ground conductor24is positioned between the line conductors20a,20b,20f,20g,21cto21e,21h, and21iand the line conductor20ein the z-axis direction.

In the high-frequency transmission line10b, the line conductors20a,20b,20f,20g,21cto21e,21h, and21iare positioned on the top surface of the dielectric sheet18bbetween the ground conductors22and24in the z-axis direction, as shown inFIG. 20. Moreover, the line conductor20eis positioned on the top surface of the dielectric sheet18e. Accordingly, the portion of the signal line20that crosses the signal line21(i.e., the line conductor20e) is positioned on the negative side in the z-axis direction relative to the ground conductor24. Therefore, in the high-frequency transmission line10b, the crossing conductor24eis a portion of the ground conductor24that overlaps with the crossing portions of the signal lines20and21.

In the high-frequency transmission line10bthus configured, the crossing conductor24e, which is kept at a ground potential, is positioned between the line conductors20eand21e. That is, the crossing conductor24efunctions as an intermediate ground conductor. Thus, as with the high-frequency transmission line10, the high-frequency transmission line10brenders it possible to significantly reduce or prevent crosstalk between the signal lines20and21.

Furthermore, in the high-frequency transmission line10b, the signal line21is positioned in its entirety on the top surface of the dielectric sheet18b, and therefore, does not extend to any dielectric sheet other than the dielectric sheet18bthrough via-hole conductors or suchlike. Accordingly, the characteristic impedance of the signal line21is more resistant to fluctuations. Therefore, the signal line20can be used as a signal line with a wider range of allowable fluctuations in characteristic impedance, and the signal line21can be used as a signal line with a narrower range of allowable fluctuations in characteristic impedance. Thus, the high-frequency transmission line10bcan be configured in accordance with the characteristics required of signal lines.

Furthermore, the high-frequency transmission line10bincludes the two ground conductors22and24but no ground conductor26. Thus, the high-frequency transmission line10brenders it possible to reduce the number of ground conductors.

Note that in the high-frequency transmission line10b, the line conductor20eof the signal line20is positioned on the negative side in the z-axis direction relative to the signal line21eand the intermediate ground conductor (i.e., the crossing conductor24e), but the line conductor20ecan be positioned on the positive side in the z-axis direction relative to the signal line21e. In such a case, a crossing conductor to serve as an intermediate ground conductor is provided so as to be positioned on the positive side in the z-axis direction relative to the signal line21eand also on the negative side in the z-axis direction relative to the signal line20e.

Third Modification

Hereinafter, a high-frequency transmission line10caccording to a third modification of a preferred embodiment of the present invention will be described with reference to the drawings.FIG. 21is an external oblique view of the high-frequency transmission line10caccording to the third modification.FIG. 22is an exploded oblique view of the high-frequency transmission line10caccording to the third modification.FIG. 23is a cross-sectional structure view of the high-frequency transmission line10caccording to the third modification.

The high-frequency transmission line10cdiffers from the high-frequency transmission line10ain that the signal lines20and21are at least partially parallel or substantially parallel to each other.

The dielectric element assembly12extends in the x-axis direction and is divided into two branches at the end on each of the positive and negative sides in the x-axis direction, as shown inFIG. 21. The dielectric element assembly12is a flexible laminate preferably formed by laminating the protective layer14and the dielectric sheets18ato18din this order from the positive side to the negative side in the z-axis direction, as shown inFIG. 22. In the following, the principal surface of the dielectric element assembly12that is located on the positive side in the z-axis direction will be referred to as a top surface, and the principal surface of the dielectric element assembly12that is located on the negative side in the z-axis direction will be referred to as a bottom surface.

The dielectric sheets18ato18d, when viewed in a plan view in the z-axis direction, have the same shape as the dielectric element assembly12. The dielectric sheets18ato18dpreferably are made of a flexible thermoplastic resin such as liquid crystal polymer or polyimide. Each of the dielectric sheets18ato18dpreferably has a thickness of, for example, about 25 μm to about 200 μm after lamination. In the following, the principal surface of each of the dielectric sheets18ato18dthat is located on the positive side in the z-axis direction will be referred to as atop surface, and the principal surface of each of the dielectric sheets18ato18dthat is located on the negative side in the z-axis direction will be referred to as a bottom surface.

The signal line20is provided in the dielectric element assembly12, and includes line conductors20a,20b, and20e, as shown inFIGS. 22 and 23. The line conductors20aand20bare linear conductors positioned on the top surface of the dielectric sheet18c, so as to extend in the x-axis direction. The line conductor20ais positioned on the negative side in the x-axis direction relative to the line conductor20band also on the negative side in the y-axis direction relative to the line conductor20b.

The line conductor20eis a linear conductor positioned on the top surface of the dielectric sheet18d, and is inclined with respect to the x-axis toward the positive side in the x-axis direction so as to point toward the positive side in the y-axis direction. The end of the line conductor20athat is located on the positive side in the x-axis direction overlaps with the end of the line conductor20ethat is located on the negative side in the x-axis direction. In addition, the end of the line conductor20athat is located on the positive side in the x-axis direction is connected to the end of the line conductor20ethat is located on the negative side in the x-axis direction by a via-hole conductor. The end of the line conductor20bthat is located on the negative side in the x-axis direction overlaps with the end of the line conductor20ethat is located on the positive side in the x-axis direction. In addition, the end of the line conductor20bthat is located on the negative side in the x-axis direction is connected to the end of the line conductor20ethat is located on the positive side in the x-axis direction by a via-hole conductor. The signal line20preferably is made of a metal material mainly composed of silver or copper and having a low specific resistance, for example.

The signal line21is provided in the dielectric element assembly12, and includes line conductors21c,21d, and21e, as shown inFIGS. 22 and 23. The line conductors21cand21dare linear conductors positioned on the top surface of the dielectric sheet18c, so as to extend in the x-axis direction. The line conductor21cis positioned on the negative side in the x-axis direction relative to the line conductor21dand also on the positive side in the y-axis direction relative to the line conductor21d. Accordingly, the line conductors20aand21care parallel or substantially parallel to each other. In addition, the line conductors20band21dare parallel to each other.

The line conductor21eis a linear conductor positioned on the top surface of the dielectric sheet18b, and is inclined with respect to the x-axis toward the positive side in the x-axis direction so as to point toward the negative side in the y-axis direction. The end of the line conductor21cthat is located on the positive side in the x-axis direction overlaps with the end of the line conductor21ethat is located on the negative side in the x-axis direction. In addition, the end of the line conductor21cthat is located on the positive side in the x-axis direction is connected to the end of the line conductor21ethat is located on the negative side in the x-axis direction by a via-hole conductor. The end of the line conductor21dthat is located on the negative side in the x-axis direction overlaps with the end of the line conductor21ethat is located on the positive side in the x-axis direction. In addition, the end of the line conductor21dthat is located on the negative side in the x-axis direction is connected to the end of the line conductor21ethat is located on the positive side in the x-axis direction by a via-hole conductor. Moreover, the line conductors20eof the signal line20and the line conductor21eof the signal line21cross each other when viewed in a plan view in the z-axis direction. The signal line21preferably is made of a metal material mainly composed of silver or copper and having a low specific resistance, for example.

The ground conductor22is provided in the dielectric element assembly12so as to be positioned on the positive side in the z-axis direction relative to the line conductors20a,20b,21c, and21d, as shown inFIGS. 22 and 23, and more specifically, the ground conductor22is positioned on the top surface of the dielectric sheet18a. The ground conductor22, when viewed in a plan view in the z-axis direction, has the same or approximately the same shape as the dielectric element assembly12, and overlaps with the signal lines20and21. More specifically, the ground conductor22overlaps with the signal line21at opposite ends of the line conductor21ebut not at other portions. The ground conductor22preferably is made of a metal material mainly composed of silver or copper and having a low specific resistance, for example.

The ground conductor24is provided in the dielectric element assembly12so as to be positioned on the negative side in the z-axis direction relative to the line conductors20a,20b,21c, and21d, as shown inFIGS. 21 and 22, and more specifically, the ground conductor24is positioned on the top surface of the dielectric sheet18d. The ground conductor24, when viewed in a plan view in the z-axis direction, has the same or approximately the same shape as the dielectric element assembly12, and overlaps with the signal lines20and21. More specifically, the ground conductor24has an opening Op2provided therein. The line conductor20eis positioned within the opening Op2. Accordingly, the ground conductor24does not overlap with the line conductor20e. The ground conductor24preferably is made of a metal material mainly composed of silver or copper and having a low specific resistance, for example.

Here, the ground conductor24preferably includes a plurality of rectangular or substantially rectangular openings30and a plurality of rectangular or substantially rectangular openings31provided therein, as shown inFIG. 22. The openings30, when viewed in a plan view in the z-axis direction, overlap with the signal line20, and are arranged along the signal line20. The openings31, when viewed in a plan view in the z-axis direction, overlap with the signal line21, and are arranged along the signal line21.

The ground conductor26is provided in the dielectric element assembly12so as to be positioned on the same surface of the dielectric sheet18con which the line conductors20a,20b,21c, and21dare positioned, as shown inFIGS. 21 and 22. The ground conductor26, when viewed in a plan view in the z-axis direction, has the same or approximately the same shape as the dielectric element assembly12. More specifically, the ground conductor26includes openings Op3to Op6provided therein. In addition, the line conductors20a,20b,21c, and21dare positioned within the openings Op3to Op6, respectively. Accordingly, the ground conductor26does not overlap with the line conductors20a,20b,21c, and21d. The ground conductor26, when viewed in a plan view in the z-axis direction, is positioned between the line conductors20eand21ein the z-axis direction, so as to overlap with the signal conductors20eand21e. The ground conductor26preferably is made of a metal material mainly composed of silver or copper and having a low specific resistance, for example.

The protective layer14covers approximately the entire top surface of the dielectric sheet18a. Accordingly, the ground conductor22is covered by the protective layer14. The protective layer14is made of, for example, a flexible resin such as a resist material.

The other features of the high-frequency transmission line10care the same as the high-frequency transmission line10a, and therefore, any descriptions thereof will be omitted.

The high-frequency transmission line10cis preferably used in a manner as will be described below.FIG. 24illustrates an electronic device200provided with the high-frequency transmission line10cas viewed in a plan view in the z-axis direction.

The electronic device200includes the high-frequency transmission line10c, circuit boards202aand202b, a battery pack (metallic body)206, a housing210, and an antenna212.

The housing210accommodates the high-frequency transmission line10c, the circuit boards202aand202b, the battery pack206, and the antenna212, as shown inFIG. 24. The circuit board202aincludes, for example, a transmission or reception circuit provided thereon. The circuit board202bincludes, for example, a power circuit (a radio frequency integrated circuit: RFIC) provided thereon. The battery pack206is, for example, a lithium-ion secondary battery, and the surface thereof is wrapped by a metal cover. The circuit board202a, the battery pack206, and the circuit board202bare arranged in this order, from the negative side to the positive side in the x-axis direction. Moreover, the antenna212is connected to the circuit board202a.

The high-frequency transmission line10cconnects the circuit boards202aand202b. Moreover, the top surface of the dielectric element assembly12(more precisely, the protective layer14) is in contact with the battery pack206. The battery pack206is fixed on the top surface of the dielectric element assembly12by an adhesive or suchlike.

The high-frequency transmission line10cthus configured has the ground conductor26provided between the line conductors20eand21e. Therefore, as with the high-frequency transmission line10a, the high-frequency transmission line10crenders it possible to significantly reduce or prevent crosstalk between the signal lines20and21.

Further, the ground conductor26is positioned at least partially between the line conductors20aand21cand also between the line conductors20band21d. Thus, crosstalk between the signal lines20and21is further significantly reduced or prevented.

Other Preferred Embodiments

The present invention is not limited to the high-frequency transmission lines10and10ato10caccording to the above preferred embodiments, and variations can be made within the spirit and scope of the present invention.

Further, the configuration of the high-frequency transmission lines10and10ato10cmay be used in combination, for example.

Note that the electronic device200is not limited to mobile communication terminals, such as cell phones, tablet computers, and notebook computers, and encompasses any device including a signal line for high-frequency signal transmission, such as digital cameras and desktop computers.

Further, the high-frequency transmission lines10and10ato10cmay be used to connect matching circuits for high-frequency signals, rather than to connect antennas and power circuits. In addition, each of the high-frequency transmission lines10and10ato10cmay be used to connect two high-frequency circuit boards.

Still further, through-hole conductors obtained by plating inner circumferential surfaces of through-holes may be used in the high-frequency transmission lines10and10ato10cin place of the via-hole conductors as described above.

Yet further, in the high-frequency transmission lines10and10ato10c, the ground conductors22and24preferably are provided in the dielectric element assembly12, for example, but they may be provided either on the top surface or the bottom surface of the dielectric element assembly12.

Note that the high-frequency transmission lines10and10ato10cmay be used on RF circuit boards such as antenna front end modules.

Further, the connectors100ato100ddo not have to be mounted on the high-frequency transmission lines10and10ato10c. In such a case, the high-frequency transmission lines10and10ato10care connected at the ends to circuit boards by soldering or suchlike. Alternatively, the connectors100ato100dmay be mounted on some ends of the high-frequency transmission lines10and10ato10c.

Still further, the connectors100ato100dare mounted on the top surfaces of the high-frequency transmission lines10and10ato10, but they may be provided on the bottom surfaces. Alternatively, for example, the connectors100aand100bmay be mounted on the top surfaces of the high-frequency transmission lines10and10ato10c, and the connector100cand100dmay be mounted on the bottom surfaces of the high-frequency transmission lines10and10ato10c.