A flexible cable for carrying RF signals and method of manufacturing same. The cable includes an elongate base substrate including a dielectric layer with an upper metal layer deposited on one side and a lower metal layer deposited on its other side. It further includes two parallel spaced-apart series of vias formed along the length of the base substrate, each via electrically interconnecting the upper metal layer and the lower metal layer, whereby a rectangular cross-sectional waveguide is provided between the upper metal layer, the lower metal layer and the two series of vias.