Coaxial cable
Coaxial cable cutaway
Coaxial cable, or coax, is an electrical cable
with an inner conductor surrounded by a tu-
bular insulating layer typically of a flexible
material with a high dielectric constant, all of
which are surrounded by a conductive layer
(typically of fine woven wire for flexibility, or
of a thin metallic foil), and finally covered
with a thin insulating layer on the outside.
The term coaxial comes from the inner con-
ductor and the outer shield sharing the same
geometric axis. Coaxial cable is used as a
transmission line for radio frequency signals,
in applications such as connecting radio
transmitters and receivers with their anten-
nas, computer network (Internet) connec-
tions, and distributing cable television sig-
nals. One advantage of coax over other types
of transmission line is that in an ideal coaxial
cable the electromagnetic field carrying the
signal exists only in the space between the
inner and outer conductors. This allows
coaxial cable runs to be installed next to met-
al objects such as gutters without the power
losses that occur in other transmission lines,
and provides protection of the signal from ex-
ternal electromagnetic interference.
Coaxial cable should not be confused with
other shielded cable used for carrying lower
frequency signals such as audio signals.
Shielded cable is similar in that it consists of
a central wire or wires surrounded by a tubu-
lar shield conductor, but it is not constructed
with the precise conductor spacing needed to
function efficiently as a radio frequency
transmission line.
History
• 1880 — Coaxial cable patented in England
by Oliver Heaviside, patent no. 1,407.[1]
• 1884 — Siemens & Halske patent coaxial
cable in Germany (Patent No. 28,978, 27
March 1884).[2]
• 1894 — Oliver Lodge demonstrates
waveguide transmission at the Royal
Institution. Nikola Tesla receives U.S.
Patent 0,514,167, Electrical Conductor, on
February 6.
• 1929 — First modern coaxial cable
patented by Lloyd Espenschied and
Herman Affel of AT&T’s Bell Telephone
La