Transmission line device comprising a plurality of substrates each having signal and ground conductor patterns thereon that are joined to each other

A transmission line device comprising:

• a plurality of substrates each including a respective transmission line including a respective insulating base material and a corresponding conductor pattern provided on the respective insulating base material, and the respective transmission line of one of two adjacent substrates of the plurality of substrates being connected to the respective transmission line of another of the two adjacent substrates;
• wherein
• the conductor patterns each include a respective signal conductor pattern, a respective signal electrode pad electrically connected to the respective signal conductor pattern, a respective ground conductor pattern, and corresponding ground electrode pads electrically connected to the respective ground conductor pattern or being a portion of the respective ground conductor pattern;
• the insulating base materials each include a resist film provided on a surface of the respective insulating base material;
• the resist films each include a respective first opening that is spaced away from an outer edge of the respective signal electrode pad in a surface direction in which the surface of the respective insulating base material extends and exposes the respective signal electrode pad, and respective second openings that define outer edges of the corresponding ground electrode pads and expose the respective ground conductor pattern;
• the plurality of substrates have an elongated shape including a length direction and a width direction;
• the respective signal electrode pad is sandwiched between the corresponding ground electrode pads in the length direction;
• and
• the respective signal electrode pad of one of the two adjacent substrates is joined to the respective signal electrode pad of another of the two adjacent substrates, and the corresponding ground electrode pads of one of the two adjacent substrates are joined to the corresponding ground electrode pads of another of the two adjacent substrates.