## Characteristic Impedance

This page explains basics of **characteristic impedance** and provides equations of characteristic impedance of various transmission lines
which include parallel line,coaxial line,shielded parallel line,stripline and so on.

Wen the reflected wave in a transmission line is zero,
the ratio of V(z)/I(z) in the direction of propagation(z) is called
characteristic impedance. It is denoted by symbol Z_{0}.

Characteristic impedance(Z_{0}) = SQRT(Z/Y) = SQRT(R+jWL/G+jWC)

Characteristic impedance of a lossy **transmission line**:

Zo = SQRT( R+jwL / G+jwC)

Characteristic impedance of a lossless transmission line:

Zo = SQRT(L/C)

### Characteristic Impedance of Transmission Lines

**Characteristic Impedance for Parallel Line**

Zo = (276/sqrt(ε))* log(2*S/d)

Where S is the spacing between two conductors and d is the diameter of the conductor.
ε is the dielectric constant between the conductors.

**Characteristic Impedance for coaxial Line**

Zo = (138/sqrt(ε))* log(D/d)

Where, D is the diameter of the outer conductor and
d is the diameter of the inner conductor.

**Characteristic Impedance for shielded parallel Line**

Zo = (276/sqrt(ε))* log (2A *(1-B^{2}/1+B^{2}))

Where,

A=s/d and B = s/D

**Characteristic Impedance for stripline**

Zo = (377/sqrt(ε) )*(T/W)

Where,

T is the thickness of the dielectric material(PCB), W is the width of the line to be etched.

### RELATED LINKS

Types and basics of microstrip line

Types and basics of transmission line

Types and basics of coaxial line

RF Terminologies

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