Transmission line member including first and third transmission line portions connected by a second coplanar waveguide portion of reduced thickness and greater width

A transmission line member comprising:

• a base body extending along a transmission direction of a high-frequency signal;
• and
• a first transmission line, a second transmission line, and a third transmission in the base body and sequentially connected along the transmission direction;
• wherein
• the base body includes:
• a first portion in which the first transmission line is provided;
• a second portion in which the second transmission line is provided;
• and
• a third portion in which the third transmission line is provided;
• the first transmission line and the third transmission line include a first signal conductor;
• the second transmission line includes a second signal conductor;
• the second portion is connected between the first portion and the third portion;
• a thickness of the second portion is smaller than a thickness of the first portion and a thickness of the third portion;
• the second transmission line is a coplanar line and includes only a conductor pattern extending more in the transmission direction than in a direction of the thickness;
• and
• a width of the second signal conductor is larger than a width of the first signal conductor.