High-frequency signal transmission line
A flexible high-frequency signal transmission line includes a dielectric body including laminated flexible dielectric layers. A signal line is provided in the dielectric body. A grounding conductor is arranged in the dielectric body to be opposed to the signal line via one of the dielectric layers. The grounding conductor is of a ladder structure including a plurality of openings and a plurality of bridges arranged alternately along the signal line. A characteristic impedance of the signal line changes between two adjacent ones of the plurality of bridges such that the characteristic impedance of the signal line rises from a minimum value to an intermediate value and to a maximum value and falls from the maximum value to the intermediate value and to the minimum value in this order.
1. A high-frequency signal transmission line comprising:
a dielectric body composed of laminated dielectric layers;
a linear signal line provided in the dielectric body; and
a first grounding conductor provided in the dielectric body so as to be opposed to the signal line via one of the dielectric layers, the first grounding conductor being of a ladder structure comprising a plurality of openings and a plurality of bridges alternately arranged in an extending direction of the signal line; wherein
the signal line has characteristic impedance that changes between two adjacent bridges such that the characteristic impedance rises from a minimum value to a first intermediate value
and to a maximum value and falls from the maximum value to a second intermediate value and to the minimum value in this order with increasing distance from one of the adjacent bridges and with decreasing distance from the other adjacent bridge; and
the signal line has a smaller width in portions opposed to the bridges than in portions having the maximum value of characteristic impedance.
2. A high-frequency signal transmission line according to claim 1 , wherein the dielectric layers are flexible.
3. A high-frequency signal transmission line according to claim 1 , wherein each of the openings has a shape that is symmetrical with respect to the signal line.
4. A high-frequency signal transmission line according to claim 1 , wherein the first grounding conductor has no other openings between two adjacent ones of the openings.
5. A high-frequency signal transmission line according to claim 1 , wherein each of the openings has a continuously decreasing width from a center of the opening to both ends in the extending direction of the signal line.
6. A high-frequency signal transmission line according to claim 1 , wherein each of the openings includes a first width in an area where the impedance of the signal line exhibits the maximum value, and includes a second width smaller than the first width in an area where the impedance of the signal line exhibits the first intermediate value, the first and second widths being dimensions in a direction perpendicular to the extending direction of the signal line.
7. A high-frequency signal transmission line according to claim 6 , wherein each of the openings has a length greater than the first width, the length being a dimension in the extending direction of the signal line.
8. A high-frequency signal transmission line according to claim 1 , further comprising a second grounding conductor arranged in the dielectric body in a position opposed to the first grounding conductor such that the signal line is sandwiched between the first grounding conductor and the second grounding conductor.
9. A high-frequency signal transmission line according to claim 8 , further comprising a via-hole conductor that pierces through the dielectric layers and that connects the first grounding conductor and the second grounding conductor to each other.
10. A high-frequency signal transmission line according to claim 8 , wherein the signal line is located closer to the first grounding conductor than to the second grounding conductor with respect to a thickness direction of the dielectric body.