A balun may include series-coupled balanced-signal lines. In some examples, a balun may include a first transmission line having a first unbalanced signal port on which an unbalanced signal may exist relative to circuit ground; a second transmission line having a first balanced-signal port may be connected in series with a third transmission line having a second balanced-signal port. In some examples, a fourth transmission line may be coupled to the first transmission line and have a third balanced-signal port. A fifth transmission line may be connected in series with the fourth transmission line and have a fourth balanced-signal port. In some examples, the transmission lines may be coaxial. Balanced signals may exist between the first and second balanced-signal ports and between the third and fourth balanced-signal ports. Series-connected coaxial transmission lines may be formed of a single coaxial line with a gap in the outer conductor separating the two coaxial transmission lines.