Abstract: A low loss leakage transmission line including a cylindrical dielectric tube the wall thickness d.sub.2 of which is selected to satisfy ##EQU1## where .epsilon..sub.1 is the dielectric constant of the internal space within the tube, .epsilon..sub.2 is the dielectric constant of the material which forms the tube, and n is a positive odd integer. A loss layer may be disposed around the cylindrical dielectric tube to capture any lost wave energy. In one embodiment, a plurality of cylindrical dielectric tubes of different dielectric constants are coaxially arranged with the wall thickness of each of the tubes satisfying the above formula.