A dielectric waveguide and/or a cable for transmission of millimeter-wave signals. The dielectric waveguide and/or the cable comprises an inner core having a dielectric medium adapted to transmit a millimeter-wave signal by carrying an electromagnetic field along the dielectric waveguide and/or the cable. The dielectric medium is a dielectric material having dielectric properties adapted to confine the propagating electromagnetic field to the inner core, while adding low transmission loss at signal frequencies in a millimeter-wave frequency range. The dielectric medium may be provided as a core of solid dielectric material, one or more bundles of fibers that extend along the length of the inner core, or as powder and/or granulate of dielectric material that fills the volume of the inner core. The dielectric material may be quartz or alumina.