| CPC H01P 3/08 (2013.01) [H05K 1/0237 (2013.01)] | 20 Claims |

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1. A transmission line to transmit a high-frequency signal, the transmission line comprising:
a laminated body including a structure in which a plurality of insulator layers is laminated in a laminated body up-down direction, the laminated body including a first section, a second section, and a third section, the first section, the second section, and the third section being arranged in this order in a transmission direction of the high-frequency signal;
a first signal conductor layer in the first section;
a second signal conductor layer in the first section, the second section, and the third section;
a third signal conductor layer in the third section;
a first interlayer connection conductor that penetrates the insulator layer in the laminated body up-down direction in the first section and electrically connects the first signal conductor layer and the second signal conductor layer to each other; and
a second interlayer connection conductor that penetrates the insulator layer in the laminated body up-down direction in the third section and electrically connects the second signal conductor layer and the third signal conductor layer to each other; wherein
the second signal conductor layer defines a coplanar line structure in the second section;
a thickness of the second section in the laminated body up-down direction is smaller than a thickness of the first section in the laminated body up-down direction and a thickness of the third section in the laminated body up-down direction;
a center of the second section in the laminated body up-down direction is above, in the laminated body up-down direction, a center of the first section in a laminated body up-down direction and a center of the third section in the laminated body up-down direction;
a distance between the second signal conductor layer and a neutral plane of the second section in the laminated body up-down direction is shorter than a distance between the first signal conductor layer and the neutral plane of the second section in the laminated body up-down direction and a distance between the third signal conductor layer and the neutral plane of the second section in the laminated body up-down direction;
a position of the second signal conductor layer in the laminated body up-down direction is above, in the laminated body up-down direction, a position of the first signal conductor layer in the laminated body up-down direction and a position of the third signal conductor layer in the laminated body up-down direction;
a length of the second signal conductor layer between the first interlayer connection conductor and the second interlayer connection conductor is equal to or less than about ½ of a wavelength of the high-frequency signal;
the plurality of insulator layers include a first layer that is an outermost layer in the laminated body up-down direction;
the first layer is included in each of the first section, the second section, and the third section; and
a portion of the first layer included in the second section is above, in the laminated body up-down direction, a portion of the first layer in the first section and a portion of the first layer in the third section.
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