Electricity: conductors and insulators – Conduits – cables or conductors – Conductive armor or sheath
Reexamination Certificate
2000-01-25
2002-01-29
Nguyen, Chau N. (Department: 2831)
Electricity: conductors and insulators
Conduits, cables or conductors
Conductive armor or sheath
C174S126200
Reexamination Certificate
active
06342677
ABSTRACT:
TECHNICAL FIELD
The present invention relates to high-frequency cables, and more particularly to a multi-layer high-frequency or coaxial cable and a method for manufacturing the same.
BACKGROUND ART
Coaxial cables and other high frequency cables are known in the art for transmitting, for example, television signals and other communication signals. As shown in
FIG. 1
, a conventional coaxial cable
100
is formed out of an inner tube
102
, a dielectric material
103
, and an outer tube
104
. The two tubes
102
,
104
are made of metal or another electrically conductive material and are disposed concentrically with the dielectric material
103
sandwiched in between the two tubes. The conductivity of the material used to form the tubes
102
,
104
and the relative permittivity and dissipation factor of the dielectric material
103
will determine the RF attenuation of the resulting coaxial cable. As is known in the art, at radio frequencies the current flowing through the tubes
102
,
104
in the cable
100
tends to flow only in and directly beneath the surfaces of the conducting tubes. This is commonly known as a “skin effect”. More particularly, current flows through and directly beneath an inside surface of the outer tube
102
and an outside surface of the inner tube
104
.
Each tube
102
,
104
is manufactured by bending a flat strip of conductive tape into a round tube and welding the longitudinal edges of the tape together to form a seam. To minimize manufacturing costs, the material selected for forming the tubes
102
,
104
is preferably one that is easy to form and weld. However, the materials that provide the best manufacturing characteristics do not necessarily offer the conductivity required for minimizing RF attenuation.
There is a need for a coaxial cable that has high conductivity, to minimize RF attenuation, and yet preserves the ease of manufacture and welding provided by less conductive materials.
SUMMARY OF THE INVENTION
Accordingly, the present invention is directed to a coaxial cable apparatus and method having a dual-layer structure for both its inner and outer tubes. Each tube is formed out of a flat strip having a base layer and a high conductivity layer disposed on the base layer. In a preferred embodiment, the high conductivity layer is disposed on less than the entire surface of the base layer, leaving the margins on the longitudinal edges of the base layer free of high conductivity material to form edge clearances. The flat strip is then bent to form a tube, with the edges of the tube being welded together. The edge clearances allow the edges of the base layer to be welded together without the weld joint touching the high conductivity layer, thereby avoiding potential problems associated with welding materials having different metallurgical properties. The preferred coaxial cable structure is arranged so that the high conductivity layer is on the outer surface of the inner tube and on the inner surface of the outer tube, following the normal current flow pattern in coaxial cables. By providing a separate high conductivity layer for each tube, the inventive dual-layer structure improves the RF attenuation characteristics of the coaxial cable while preserving the ease of manufacture provided by the material used in the base layer.
REFERENCES:
patent: 3340353 (1967-09-01), Mildner
patent: 3715453 (1973-02-01), Aupoix et al.
patent: 4439633 (1984-03-01), Grooten
patent: 4510346 (1985-04-01), Bursh, Jr. et al.
patent: 5111002 (1992-05-01), Hollander
patent: 6010788 (2000-01-01), Kebabjian et al.
patent: 6246008 (2001-06-01), Fluckiger et al.
Nguyen Chau N.
Rader & Fishman & Grauer, PLLC
Trilogy Communications, Inc.
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