# Characteristic impedance vs Wave impedance

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#### mig-11101

##### Junior Member level 3 Hi,

Could anyone help me on this question -

What is difference between characteristic and wave impedance for a transmission line?

As I do understand, both are defined as voltage/current(or E and H vectors) amplitude relation, but wave impedance is given for infinite transmission line, while characteristic impedance - for finite. Is this correct?

Thanks!

#### tony_lth Wave impedance - Wikipedia, the free encyclopedia
The wave impedance of an electromagnetic wave is the ratio of the transverse components of the electric and magnetic fields (the transverse components being those at right angles to the direction of propagation). For a transverse-electric-magnetic (TEM) plane wave traveling through a homogeneous medium, the wave impedance is everywhere equal to the intrinsic impedance of the medium. In particular, for a plane wave travelling through empty space, the wave impedance is equal to the impedance of free space. The symbol Z is used to represent it and it is expressed in units of ohms. The symbol η (eta) may be used instead of Z for wave impedance to avoid confusion with electrical impedance.

Characteristic impedance - Wikipedia, the free encyclopedia
The characteristic impedance or surge impedance of a uniform transmission line, usually written Z0, is the ratio of the amplitudes of a single pair of voltage and current waves propagating along the line in the absence of reflections. The SI unit of characteristic impedance is the ohm. The characteristic impedance of a lossless transmission line is purely real, that is, there is no imaginary component (Z0 = | Z0 | + j0). Characteristic impedance appears like a resistance in this case, such that power generated by a source on one end of an infinitely long lossless transmission line is transmitted through the line but is not dissipated in the line itself. A transmission line of finite length (lossless or lossy) that is terminated at one end with a resistor equal to the characteristic impedance (ZL = Z0) appears to the source like an infinitely long transmission line.

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