WHY COAXIAL CABLES?
A coaxial cable consists of two concentric conductors, which are seperated by a dielectric and by a screen. Fields of applocation for coaxial cables are video technology, electrical measurement as well as applications, where radio signals have to be transferred without loss.
A double screened coaxial cable is presented here
Structure of a double screened coaxial cable:
1 = inner conductor – solid wire or stranded wires (1b)
2 = dielectric / isolation
3a = braid or foil
3b = braid or foil
4 = outer sheath
more information about the structure of such cables: Structure coaxial cable
The wave impedance is only depending on the outer diameter of the inner conductor, the inner diameter of the outer conductor and the dielectric constant of the intermediate dielectric. A vacuum is the best dielectric.