A coaxial line consists of two concentric cylindrical conductors (see Figure 4.2), where *R*_{i} and *R*_{o} are the inner and outer radius, respectively. The two conductors are separated by a homogeneous dielectric material with a relative permittivity of ε_{r}. The voltage *U* between the inner and outer conductor corresponds to a radial electric field strength *E*_{R} and the current *I* in the conductors produces a circulating magnetic field strength *H*_{φ}.

In the following sections we will derive the transmission line parameters of a coaxial line. The cylindrical symmetry of the problem allows a mathematically quite simple treatment using cylindrical coordinates. In our considerations we employ our knowledge of electromagnetic theory from Chapter 2 and the definitions from the transmission line theory in Chapter 3.

Let us consider a loss-less transmission line. We can calculate the characteristic impedance *Z*_{0} from the inductance per unit length *L*′, the material parameters ε_{r} and μ_{r} and the light speed in vacuum *c*_{0} (see Equation 3.69).

Technical transmission lines commonly use dielectric, non-magnetic materials. Hence, we set μ ...

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