US Patent 9117572 Foamed coaxial cable and multicore cable

A foamed axial cable includes a pair of signal conductors, an insulation covering a periphery of the signal conductor and formed of a foamed material, a skin layer covering a periphery of the insulation and formed of a non-foamed material, and a shield conductor on a periphery of the skin layer. An outer surface of the skin layer or an inner surface of the shield conductor includes a fine groove formed thereon so as to have a void between the skin layer and the shield conductor.