Transmission line

A transmission line comprising:

• a dielectric base body that includes a plurality of dielectric layers stacked on top of one another;
• a first signal conductor and a second signal conductor that are adjacent to or in a vicinity of each other inside the dielectric base body and that extend in a transmission direction of a high-frequency signal;
• a first ground conductor located on a first side with respect to the first signal conductor and the second signal conductor in a thickness direction of the dielectric base body, the first ground conductor overlapping the first signal conductor and the second signal conductor over substantially entire lengths of the first signal conductor and the second signal conductor when viewed in the thickness direction;
• a second ground conductor located on a second side opposite to the first side with respect to the first signal conductor and the second signal conductor in the thickness direction of the dielectric base body, the second ground conductor including:
• a main conductor portion located between the first signal conductor and the second signal conductor when the plurality of dielectric layers are viewed in the thickness direction and extending along the first signal conductor and the second signal conductor;
• a first auxiliary conductor portion connected to the main conductor portion and extending from the main conductor portion to a first-signal-conductor-side lateral surface of the dielectric base body, the first-signal-conductor-side lateral surface extending along the first signal conductor and the second signal conductor;
• and
• a second auxiliary conductor portion connected to the main conductor portion and extending from the main conductor portion to a second-signal-conductor-side lateral surface of the dielectric base body, the second-signal-conductor-side lateral surface extending along the first signal conductor and the second signal conductor;
• a first lateral-surface conductor connecting the first ground conductor and the first auxiliary conductor portion to each other on the first-signal-conductor-side lateral surface;
• and
• a second lateral-surface conductor connecting the first ground conductor and the second auxiliary conductor portion to each other on the second-signal-conductor-side lateral surface.