An electronic device includes a housing including a first plate facing in a first direction, a second plate facing in a second direction, and a side member surrounding a space between the first plate and the second plate, a support member interposed between the first plate and the second plate and including a metallic structure, an antenna structure mounted on the support member and including a first surface facing in a third direction toward the side member, and a polymer structure disposed in a space surrounded by the first plate, the support member, the side member, and the first surface of the antenna structure, and coupled to the metallic structure. The coupled metallic structure and polymer structure includes a groove bounded by the first surface, a second surface on the polymer structure forming an acute angle with the first surface, and a third surface substantially perpendicular to the second surface.