A flexible dielectric waveguide for transmission of millimeter-wave signals, comprising an inner core comprising a dielectric medium adapted to transmit a millimeter-wave signal by carrying an electromagnetic field along the dielectric waveguide; wherein the dielectric medium comprises a powder and/or a granulate of a dielectric material that fills a volume of the inner core, said 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; and a cladding made of a polymer material having a loss tangent lower than 0.001 at frequencies in said millimeter-wave frequency range that is directly adjacent to said inner core and surrounds the inner core so as to reinforce the confinement of the electromagnetic field to the inner core at frequencies in said millimeter-wave frequency range; wherein the dielectric material of said powder and/or granulate is quartz with a dielectric constant higher than 4.0 and a loss tangent lower than 0.0001 in said millimeter-wave frequency range or an alumina with a dielectric constant of about 9.0 and a loss tangent lower than 0.0007 at frequencies around 100 GHz; said dielectric medium comprising said powder and/or granulate of dielectric material is characterized by an effective dielectric constant higher than 3.0 and a loss tangent lower than 0.001 at signal frequencies in said millimeter-wave frequency range; and said cladding is made of polytetrafluoroethylene having a dielectric constant of about 2.1 and a loss tangent of 0.00015 at 10 GHz or a combination of polytetrafluoroethylene and polyethylene. an inner core comprising a dielectric medium adapted to transmit a millimeter-wave signal by carrying an electromagnetic field along the dielectric waveguide; wherein the dielectric medium comprises a powder and/or a granulate of a dielectric material that fills a volume of the inner core, said 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; and a cladding made of a polymer material having a loss tangent lower than 0.001 at frequencies in said millimeter-wave frequency range that is directly adjacent to said inner core and surrounds the inner core so as to reinforce the confinement of the electromagnetic field to the inner core at frequencies in said millimeter-wave frequency range; wherein the dielectric material of said powder and/or granulate is quartz with a dielectric constant higher than 4.0 and a loss tangent lower than 0.0001 in said millimeter-wave frequency range or an alumina with a dielectric constant of about 9.0 and a loss tangent lower than 0.0007 at frequencies around 100 GHz; said dielectric medium comprising said powder and/or granulate of dielectric material is characterized by an effective dielectric constant higher than 3.0 and a loss tangent lower than 0.001 at signal frequencies in said millimeter-wave frequency range; and said cladding is made of polytetrafluoroethylene having a dielectric constant of about 2.1 and a loss tangent of 0.00015 at 10 GHz or a combination of polytetrafluoroethylene and polyethylene.