Stem

1. A stem, comprising: a stem body that has a first surface to be placed on a flexible substrate, a second surface opposite to the first surface, and a through hole passing through the first surface and the second surface; a cylindrical body that is fitted into the through hole of the stem body; and a lead that is inserted into the cylindrical body and fixed to the cylindrical body with a fixing member and that has an end portion protruding from the first surface of the stem body, wherein the cylindrical body has a protrusion that protrudes toward the flexible substrate from the first surface of the stem body, surrounds an outer circumferential surface of the end portion of the lead, and separates, with the stem body placed on the flexible substrate, a gap between the stem body and the flexible substrate, and the outer circumferential surface of the end portion of the lead, and a length of the protrusion, in a direction extending perpendicularly from the first surface of the stem body, defines a width of the gap, in the direction extending perpendicularly from the first surface of the stem body, between the stem body and the flexible substrate on which the stem body is placed, wherein, with the stem body placed on the flexible substrate, the protrusion directly contacts the flexible substrate.

2. The stem according to claim 1 , wherein the protrusion is to be bonded to a grounding pattern of the flexible substrate.

3. The stem according to claim 1 , wherein the cylindrical body has an air layer that is not filled with the fixing member between the protrusion and the outer circumferential surface of the end portion of the lead.

4. The stem according to claim 1 , wherein

the lead transmits a high frequency signal, and

the fixing member has a relative dielectric constant lower than a relative dielectric constant of another fixing member that fixes another lead different from the lead.