Electricity: conductors and insulators – Conduits – cables or conductors – Conductive armor or sheath
Reexamination Certificate
1998-09-15
2001-03-13
Kincaid, Kristine (Department: 2831)
Electricity: conductors and insulators
Conduits, cables or conductors
Conductive armor or sheath
C174S1060SC
Reexamination Certificate
active
06201190
ABSTRACT:
FIELD OF INVENTION
The present invention concerns a coaxial cable having an inner conductor and an outer conductor. The outer conductor utilizes a braidless design having dual foil tapes.
BACKGROUND OF THE INVENTION
Coaxial cables are well-known. A coaxial cable includes a central conductor. A coaxial cable also includes an outer conductor coaxial to and outside the central conductor. The outer conductor can be a metallic tube conductor or a braid conductor or a foil shield conductor. Generally, a dielectric in the form of spacers or a solid continuous extrusion electronically insulates and separates the central conductor from the outer conductor. The central conductor typically transmits very low voltage current in the form of signals. The signals are typically audio signals, data signals, voice signals, video signals, television signals, or other types of signals.
The outer conductor serves three primary functions. First, it is used to prevent external radiation or noise from affecting the signal transmitted on the central conductor. Second, it prevents signal leakage from the central conductor. Third, the outer conductor, normally at ground potential, acts as a return path for the signal (current) passing through the central conductor.
FIELD OF THE INVENTION
Industry recognizes that braided outer conductors of copper or similar materials provide flexibility and durability. The braided shield to provide effective flexibility needs to have a tiny amount of space between the wires of the braid. To eliminate space, fine wire is braided and/or double braid layers are used. The use of fine wire and double layering, however, may make the shield excessively stiff, large or heavy, and laborious to manufacture.
As an alternative to braided design, industry has used foil shielding. Typically the foil shield is made of a foil tape. A known type of foil tape utilizes aluminum bonded to polyester. The foil tape can include an adhesive so the foil tape can bond to the dielectric surrounding the central conductor. Foil shields eliminate the wire spacing problems associated with braids and generally improve shielding coverage over braided designs. Foil shielding, however, suffers from rupture.
To obtain the shielding benefits of foil tape and the durability of a braid, industry has used a foil tape (foil shield) surrounded by a metallic braid. Unfortunately, the use of a braid increases cost because braiding is slow and labor-intensive. Also, the use of the braid results in a heavier cable with a larger diameter than the cables utilizing only a foil shield.
The present invention improves upon the outer conductor of a coaxial cable. The invention utilizes a first foil shield surrounding the central conductor. The first foil shield is not helically wrapped, but rather is applied longitudinally in a cigarette-wrap configuration. A second foil shield surrounds the first foil shield and is also applied longitudinally in a cigarette wrap. The second foil shield contacts the first foil shield. The second foil shield is in electrical conductive contact with the first foil shield. The outer conductor is thus braidless.
The coaxial cable, by eliminating the braid, improves termination ability. An installer, when hooking the cable to a connector, does not have to comb back the braid over the jacket. Eliminating the braid also improves the integrity of the cable-to-connector interface. The elimination of the braid further reduces cost because the second foil shield is more economical to use than a braid. Elimination of the braid has the further advantage of reducing the diameter of the cable from that of cable utilizing a braid, while providing performance as good as a single-foil/single-braid combination.
DESCRIPTION OF THE RELATED ART
Previous coaxial cables (U.S. Pat. Nos. 5,321,202; 5,521,331; 5,414,213) have utilized a second foil shield. However, in these cables the second foil shield is separated from the first foil shield by an intermediate dielectric. The present invention, by eliminating the intermediate dielectric, reduces the cost of the cable. Also, by eliminating the intermediate dielectric, the present cable maintains electrical performance over a greater range of cable stress. Eliminating the dielectric allows the first and second foil shields to be in electrical contact. Having the first and second foil shields in electrical contact assures continuity in case of rupture.
A previous double-shielded electric cable (U.S. Pat. No. 3,340,353) is also known. In this design, the second shield is applied to solve the problem of cable termination. The cables previous to this known cable's design utilized a foil shield bonded to a polymer jacket. Bonding the foil to the jacket, however, made it difficult to terminate the cable to a connector because peeling back the jacket destroyed the foil bonded to the jacket. The double-shielded cable, by applying a second, thinner foil shield to the first foil shield, allows for easier termination. The peeling back of the jacket destroys only the second, thinner foil shield, leaving the first foil shield undisturbed.
The previous double-shielded cable, however, does not disclose or suggest substituting a second foil shield to maintain an outer conductor's electrical performance over a greater range of cable stress. The thinness of the second shield means that it is not installed to add durability to the outer conductor. The second shield, rather, is applied sacrificially for the purpose of being destroyed during termination. Thus, one would not substitute the second foil shield for a braid.
A communication cable (U.S. Pat. No. 3,636,234) having a first foil shield of copper or aluminum and a second foil shield of tinned annealed steel is also known. The second foil shield is helically wrapped. The use of the tinned annealed steel indicates that the cable is designed to increase the range of noise from which the cable is shielded. Aluminum shields it from high-frequency RF waves and steel shields it from low-frequency magnetic waves.
The cable does not disclose or suggest substituting a second foil shield to maintain the outer conductor's shielding ability over a greater range of cable stress. The steel shielding does not provide continuity in the event of micro-fractures in the aluminum tape because the steel tape shields different frequencies. Alternatively, the aluminum tape does not offer continuity in shielding in the event of micro-fractures in the steel tape because the aluminum tape shields different frequencies. Thus, the aluminum/steel double-shielded design discloses increasing the range of shielding but not maintaining shielding continuity over a greater range of cable stress.
Applicant, however, by utilizing dual aluminum tapes, maintains the outer conductor's shielding ability over a greater range of stress. If the inner shield micro-fractures, the outer shield will offer shielding continuity. If the outer shield micro-fractures, the inner shield will offer shielding continuity. If both shields fracture, the micro-fractures will likely not line up. Thus, the fractured portion of the shield will be covered by a non-fractured portion of the adjacent shield. Therefore the shield will have continuity even if both shields micro-fracture.
Also, by utilizing a second longitudinally-wrapped shield rather than a helically-wrapped shield, applicant improves electrical performance. The longitudinally-wrapped shield prevents the inductance caused by the helically-wrapped shield. By eliminating the inductance, applicant improves the integrity of the signal.
BRIEF SUMMARY OF THE INVENTION
Applicant desires to provide a coaxial cable that maintains shielding ability over a greater range of cable stress than a single shield design but does not suffer from the negative side effects of utilizing a braid, which include slow and laborious braiding, large diameter and heavier cable. It is also desired that the cable have the same electrical performance as a single-foil/single-braid design. Accordingly, applicant provides a coaxial cable compose
Belden Wire & Cable Company
Conte Robert F. I.
Kincaid Kristine
Lee Mann Smith McWilliams Sweeney & Ohlson
Mayo III William H.
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