A waveguide is provided that includes an elongate dielectric inner region, and an electrically conducting outer region spaced apart from the dielectric inner region. The dielectric inner region may be arranged to be flexible, and in some examples may be formed from powdered dielectric contained in a polymer tube or matrix, or in other examples may be formed from a plurality of segments. In some examples of the waveguide, each segment may be formed to have lenticular end faces, and may be formed from sintered BaTi4O9.