Abstract: A signal carrying structure comprising a planar conductive member having a major surface, a dielectric layer having a substantially constant thickness, and a conductive track. A first major surface of the dielectric layer is in contact with the major surface of the planar conductive member, and the conductive track is in contact with a second major surface of the dielectric layer. The conductive track is spaced from the major surface of the planar conductive member by the dielectric layer. The dielectric layer has a plurality of apertures which extend between the first and second major surfaces thereof in the region between the conductive track and the planar conductive member. The proportion of dielectric material in the dielectric layer is less in this region than in the other regions of the dielectric layer. The structure is used for propagating microwave electromagnetic radiation, and is applicable to strip line, triplate and phased array antenna applications.