High-frequency signal transmission line and electronic apparatus

1. An electronic apparatus comprising a high-frequency signal transmission line and a metal article that are disposed in a casing, the high-frequency signal transmission line comprising:

a laminate that is obtained by laminating insulating layers and has a first main surface and a second main surface;

a linear signal line disposed in the laminate;

a first ground conductor that is disposed in the laminate, faces the signal line via one of the insulating layers, and continuously extends along the signal line, wherein in a portion of the first ground conductor facing the signal line substantially, no opening is disposed and wherein the first ground conductor is located near the first main surface with respect to the signal line; and

a second ground conductor that is disposed in the laminate, faces the first ground conductor via the signal line sandwiched therebetween, and has a plurality of openings arranged along the signal line, wherein the second ground conductor is located near the second main surface with respect to the signal line;

wherein the linear signal line, the first ground conductor and the second ground conductor define a stripline having a triplate structure;

wherein a main surface of the high-frequency signal transmission line near the first ground conductor with respect to the signal line is in contact with the metal article; and

wherein a main surface of the high-frequency signal transmission line near the second ground conductor with respect to the signal line is opposed to the casing at a specified distance.

2. The electronic apparatus according to claim 1 , wherein the first main surface is fixed to the article.

3. The electronic apparatus according to claim 1 , wherein the first ground conductor is electrically connected to the metal article.

4. The electronic apparatus according to claim 1 ,

wherein the first ground conductor is disposed on one of the insulating layers nearest to the first main surface; and

wherein the second ground conductor is disposed between ones of the insulating layers.

5. The electronic apparatus according to claim 1 , wherein the laminate further includes a protection layer covering the first ground conductor.

6. The electronic apparatus according to claim 1 , further comprising a connector that is attached to the laminate and includes a signal terminal electrically connected to the signal line and a ground terminal electrically connected to the first ground conductor and the second ground conductor.

7. The electronic apparatus according to claim 1 , wherein the plurality of openings are arranged at regular intervals.

8. The electronic apparatus according to claim 1 ,

wherein the second ground conductor has a ladder shape obtained by alternately forming the plurality of openings and bridge portions along the signal line; and

wherein a characteristic impedance of the signal line changes between two adjacent ones of the bridges in such a manner that, with increasing distance from one of the two adjacent bridge portions and with decreasing distance to the other bridge portion, the characteristic impedance increases in an order of a minimum value, a first intermediate value, and a maximum value and then decreases in an order of the maximum value, a second intermediate value, and the minimum value.

9. The electronic apparatus according to claim 1 , wherein the laminate has flexibility.

10. The electronic apparatus according to claim 1 , further comprising:

an adhesive layer formed on the first main surface; and

a cover layer releasably attached to the adhesive layer;

wherein the high-frequency signal transmission line is fixed to the article via the adhesive layer from which the cover layer has been detached.

11. The electronic apparatus according to claim 10 ,

wherein the first ground conductor is disposed on the first main surface; and

wherein the adhesive layer is made of a conductive adhesive, and is formed on the first ground conductor.

12. The electronic apparatus according to claim 11 ,

wherein the article has a conductive portion; and

wherein the first ground conductor is electrically connected to the conductive portion of the article via the adhesive layer.

13. The electronic apparatus according to claim 11 , wherein the metal article is maintained at a ground potential.

14. An electronic apparatus comprising a high-frequency signal transmission line and a metal article that are disposed in a casing, the high-frequency signal transmission line comprising:

an element assembly having a first main surface and a second main surface; a linear signal line disposed in the element assembly;

a linear signal line disposed in the element assembly;

a first ground conductor that is disposed on a side of the first main surface with respect to the signal line in the element assembly and faces the signal line, wherein in a portion of the first ground conductor facing the signal line, substantially no opening is disposed; and

a second ground conductor that faces the first ground conductor via the signal line sandwiched therebetween in the element assembly, and has an opening arranged along the signal line, wherein the second ground conductor is located near the second main surface with respect to the signal line; and

an adhesive layer formed on the first main surface;

wherein the linear signal line, the first ground conductor and the second ground conductor define a stripline having a triplate structure;

wherein the high-frequency signal transmission line is fixed to the article via the adhesive layer; and

wherein a main surface of the high-frequency signal transmission line near the second ground conductor with respect to the signal line is opposed to the casing at a specified distance.