A triangular stepped helical aerial, that is a helical aerial in which the axial length varies in discrete steps rather than continuously, has the same relative wideband radiation and impedance characteristics of a conventional axial-mode helical aerial, despite its discontinuous structure. The observed radiation and impedance characteristics of an equilateral-triangular stepped helix radiating in the axial mode are reported.The method of deriving the far field of such an aerial is outlined, assuming an unattenuated travelling wave along the length of the conductor.