Characteristic impedance
In
radio communications,
characteristic impedance (
Z0) of a uniform
transmission line is the
impedance of a
circuit that, when connected to the
output terminals of a line of arbitrary length, causes the line to appear infinitely long.
A uniform line terminated in its characteristic impedance will have no standing waves, no reflections from the end, and a constant ratio of voltage to current at a given frequency at every point on the line.
If the line is not uniform, the iterative impedance must be used.
The characteristic impedance of a linear, homogeneous, isotropic, dielectric propagation medium free of electric charge is given by the relation
where μ is the magnetic permeability and ε is the electric permittivity of the
medium. Where the magnetic permeability and electric permittivity of the
vacuum are used, this equation defines a fundamental physical constant, the
characteristic impedance of free space and turns out to be equal to 120π (about 377) ohms.
See also:
Adapted from
Federal Standard 1037C.