U.S. patent application number 10/611478 was filed with the patent office on 2004-08-05 for coaxial cable having wide continuous usable bandwidth.
Invention is credited to Blew, Douglas J., Gialenios, Michael, Story, Christopher Alan, Wessels, Robert A. JR., Wyatt, Frank B. II.
Application Number | 20040151446 10/611478 |
Document ID | / |
Family ID | 34062341 |
Filed Date | 2004-08-05 |
United States Patent
Application |
20040151446 |
Kind Code |
A1 |
Wyatt, Frank B. II ; et
al. |
August 5, 2004 |
Coaxial cable having wide continuous usable bandwidth
Abstract
A coaxial cable includes: a metallic inner conductor formed of a
first material and having a first thickness; a dielectric layer
circumferentially surrounding the inner conductor formed of a
second material and having a second thickness; a metallic outer
conductor circumferentially surrounding the dielectric layer formed
of a third material and having a third thickness; and a polymeric
jacket circumferentially surrounding the outer conductor formed of
a fourth material and having a fourth thickness.
Inventors: |
Wyatt, Frank B. II;
(Hickory, NC) ; Wessels, Robert A. JR.; (Hickory,
NC) ; Story, Christopher Alan; (Hickory, NC) ;
Blew, Douglas J.; (Mooresville, NC) ; Gialenios,
Michael; (Charlotte, NC) |
Correspondence
Address: |
MYERS BIGEL SIBLEY & SAJOVEC
PO BOX 37428
RALEIGH
NC
27627
US
|
Family ID: |
34062341 |
Appl. No.: |
10/611478 |
Filed: |
July 1, 2003 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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10611478 |
Jul 1, 2003 |
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10192215 |
Jul 10, 2002 |
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Current U.S.
Class: |
385/100 ;
348/E7.07; 348/E7.094; 385/123 |
Current CPC
Class: |
H01B 11/1878 20130101;
H04N 7/17309 20130101; H04N 21/6118 20130101; H01B 11/1895
20130101; H01B 11/22 20130101; H04N 7/22 20130101 |
Class at
Publication: |
385/100 ;
385/123 |
International
Class: |
G02B 006/44 |
Claims
That which is claimed is:
1. A coaxial cable, comprising: a metallic inner conductor formed
of a first material and having a first thickness; a dielectric
layer circumferentially surrounding the inner conductor formed of a
second material and having a second thickness; a metallic outer
conductor circumferentially surrounding the dielectric layer formed
of a third material and having a third thickness; and a polymeric
jacket circumferentially surrounding the outer conductor formed of
a fourth material and having a fourth thickness; wherein at least
one of the first material, first thickness, second material, second
thickness, third material, third thickness, fourth material and
fourth thickness is selected so that the cable has: (a) a usable
bandwidth between about 5 MHz and the cut-off frequency of the
cable; (b) a minimum bend radius of less than about 5 times the
jacket outer diameter; and (c) a velocity of propagation of greater
than about 88.
2. The coaxial cable defined in claim 1, wherein at least one of
the first material, first thickness, second material, second
thickness, third material, third thickness, fourth material and
fourth thickness is further selected so that the cable has a
continuous usable bandwidth above about 1.0 GHz.
3. The coaxial cable defined in claim 1, wherein at least one of
the first material, first thickness, second material, second
thickness, third material, third thickness, fourth material and
fourth thickness is further selected so that the cable has a
continuous bandwidth above about 3.0 GHz.
4. The coaxial cable defined in claim 1, wherein at least one of
the first material, first thickness, second material, second
thickness, third material, third thickness, fourth material and
fourth thickness is further selected so that the cable has a return
loss of at least about -15 db.
5. The coaxial cable defined in claim 1, wherein at least one of
the first material, first thickness, second material, second
thickness, third material, third thickness, fourth material and
fourth thickness is further selected so that the cable has a return
loss of at least about -25 db.
6. The coaxial cable defined in claim 1, wherein at least one of
the first material, first thickness, second material, second
thickness, third material, third thickness, fourth material and
fourth thickness is further selected so that the cable has a
nominal impedance of 75 ohms.
7. The coaxial cable defined in claim 1, wherein at least one of
the first material, first thickness, second material, second
thickness, third material, third thickness, fourth material and
fourth thickness is further selected so that the cable has a
nominal impedance of 50 ohms.
8. The coaxial cable defined in claim 1, wherein at least one of
the first material, first thickness, second material, second
thickness, third material, third thickness, fourth material and
fourth thickness is further selected so that the cable has an
attenuation spike due to return loss within the usable
bandwidth.
9. The coaxial cable defined in claim 1, wherein the cable has a
length of at least 1,000 feet.
10. The coaxial cable defined in claim 1, wherein the first
material is selected from the group consisting of: copper; aluminum
and steel clad with copper; and aluminum, copper and steel clad
with silver.
11. The coaxial cable defined in claim 1, wherein the second
material is a foamed polymeric material.
12. The coaxial cable defined in claim 11, wherein the dielectric
layer has a density gradient across its cross-section such that
density increases with increasing radial distance from the
conductor.
13. The coaxial cable defined in claim 1, wherein the third
material is selected from the group consisting of solid copper and
solid aluminum.
14. The coaxial cable defined in claim 1, wherein a
corrosion-resistant material is interposed between the outer
conductor and the jacket.
15. The coaxial cable defined in claim 16, wherein the
corrosion-resistant material is a dry material.
16. The coaxial cable defined in claim 1, wherein the cable
withstands at least 5 cycles in reverse bend fatigue tests.
17. The coaxial cable defined in claim 1, wherein the dielectric
layer can be cored from the cable with a conventional coring tool
such that less than a 360 degree residue remains on the inner
surface of the outer conductor.
18. A coaxial cable, comprising: a metallic inner conductor formed
of a first material and having a first thickness; a dielectric
layer circumferentially surrounding the inner conductor formed of a
second material and having a second thickness; a metallic outer
conductor circumferentially surrounding the dielectric layer formed
of a third material and having a third thickness; and a polymeric
jacket circumferentially surrounding the outer conductor formed of
a fourth material and having a fourth thickness; wherein at least
one of the first material, first thickness, second material, second
thickness, third material, third thickness, fourth material and
fourth thickness is selected so that the dielectric layer can be
cored from the cable with a standard coring tool such that less
than a 360 degree residue remains on the inner surface of the outer
conductor and so that the cable has: (a) a usable bandwidth between
about 5 MHz and the cut-off frequency of the cable; and (b) a
minimum bend radius of less than about 5 times the jacket outer
diameter.
19. The coaxial cable defined in claim 18, wherein at least one of
the first material, first thickness, second material, second
thickness, third material, third thickness, fourth material and
fourth thickness is further selected so that the cable has a
continuous usable bandwidth above about 1.0 GHz.
20. The coaxial cable defined in claim 18, wherein at least one of
the first material, first thickness, second material, second
thickness, third material, third thickness, fourth material and
fourth thickness is further selected so that the cable has a
continuous bandwidth above about 3.0 GHz.
21. The coaxial cable defined in claim 18, wherein at least one of
the first material, first thickness, second material, second
thickness, third material, third thickness, fourth material and
fourth thickness is further selected so that the cable has a return
loss of at least about -15 db.
22. The coaxial cable defined in claim 18, wherein at least one of
the first material, first thickness, second material, second
thickness, third material, third thickness, fourth material and
fourth thickness is further selected so that the cable has a return
loss of at least about -25 db.
23. The coaxial cable defined in claim 18, wherein at least one of
the first material, first thickness, second material, second
thickness, third material, third thickness, fourth material and
fourth thickness is further selected so that the cable has a
nominal impedance of 75 ohms.
24. The coaxial cable defined in claim 18, wherein at least one of
the first material, first thickness, second material, second
thickness, third material, third thickness, fourth material and
fourth thickness is further selected so that the cable has a
nominal impedance of 50 ohms.
25. The coaxial cable defined in claim 18, wherein at least one of
the first material, first thickness, second material, second
thickness, third material, third thickness, fourth material and
fourth thickness is further selected so that the cable has an
attenuation spike due to return loss within the usable
bandwidth.
26. The coaxial cable defined in claim 18, wherein the cable has a
length of at least 1,000 feet.
27. The coaxial cable defined in claim 18, wherein the first
material is selected from the group consisting of: copper; aluminum
and steel clad with copper; and aluminum, copper and steel clad
with silver.
28. The coaxial cable defined in claim 18, wherein the second
material is a foamed polymeric material.
29. The coaxial cable defined in claim 28, wherein the dielectric
layer has a density gradient across its cross-section such that
density increases with increasing radial distance from the
conductor.
30. The coaxial cable defined in claim 18, wherein the third
material is selected from the group consisting of solid copper and
solid aluminum.
31. The coaxial cable defined in claim 18, wherein a
corrosion-resistant material is interposed between the outer
conductor and the jacket.
32. The coaxial cable defined in claim 31, wherein the
corrosion-resistant material is a dry material.
33. The coaxial cable defined in claim 18, wherein the cable
withstands at least 5 cycles in reverse bend fatigue tests.
34. A coaxial cable, comprising: a metallic inner conductor formed
of a first material and having a first thickness; a dielectric
layer circumferentially surrounding the inner conductor formed of a
second material and having a second thickness; a metallic outer
conductor circumferentially surrounding the dielectric layer formed
of a third material and having a third thickness; and a polymeric
jacket circumferentially surrounding the outer conductor formed of
a fourth material and having a fourth thickness; wherein at least
one of the first material, first thickness, second material, second
thickness, third material, third thickness, fourth material and
fourth thickness is selected so that the dielectric layer can be
cored from the cable with a standard coring tool such that less
than a 360 degree residue remains on the inner surface of the outer
conductor and so that the cable has: (a) a usable bandwidth between
about 5 MHz and the cut-off frequency of the cable; and (b) a
velocity of propagation of greater than about 88 percent.
35. The coaxial cable defined in claim 34, wherein at least one of
the first material, first thickness, second material, second
thickness, third material, third thickness, fourth material and
fourth thickness is further selected so that the cable has a
continuous usable bandwidth above about 1.0 GHz.
36. The coaxial cable defined in claim 34, wherein at least one of
the first material, first thickness, second material, second
thickness, third material, third thickness, fourth material and
fourth thickness is further selected so that the cable has a
continuous bandwidth above about 3.0 GHz.
37. The coaxial cable defined in claim 34, wherein at least one of
the first material, first thickness, second material, second
thickness, third material, third thickness, fourth material and
fourth thickness is further selected so that the cable has a return
loss of at least about -15 db.
38. The coaxial cable defined in claim 34, wherein at least one of
the first material, first thickness, second material, second
thickness, third material, third thickness, fourth material and
fourth thickness is further selected so that the cable has a return
loss of at least about -25 db.
39. The coaxial cable defined in claim 34, wherein at least one of
the first material, first thickness, second material, second
thickness, third material, third thickness, fourth material and
fourth thickness is further selected so that the cable has a
nominal impedance of 75 ohms.
40. The coaxial cable defined in claim 34, wherein at least one of
the first material, first thickness, second material, second
thickness, third material, third thickness, fourth material and
fourth thickness is further selected so that the cable has a
nominal impedance of 50 ohms.
41. The coaxial cable defined in claim 34, wherein at least one of
the first material, first thickness, second material, second
thickness, third material, third thickness, fourth material and
fourth thickness is further selected so that the cable has an
attenuation spike due to return loss within the usable
bandwidth.
42. The coaxial cable defined in claim 34, wherein the cable has a
length of at least 1,000 feet.
43. The coaxial cable defined in claim 34, wherein the first
material is selected from the group consisting of: copper; aluminum
and steel clad with copper; and aluminum, copper and steel clad
with silver.
44. The coaxial cable defined in claim 34, wherein the second
material is a foamed polymeric material.
45. The coaxial cable defined in claim 44, wherein the dielectric
layer has a density gradient across its cross-section such that
density increases with increasing radial distance from the
conductor.
46. The coaxial cable defined in claim 34, wherein the third
material is selected from the group consisting of solid copper and
solid aluminum.
47. The coaxial cable defined in claim 34, wherein a
corrosion-resistant material is interposed between the outer
conductor and the jacket.
48. The coaxial cable defined in claim 47, wherein the
corrosion-resistant material is a dry material.
49. The coaxial cable defined in claim 34, wherein the cable
withstands at least 5 and cycles in reverse bend fatigue tests.
50. A hybrid fiber cable (HFC) network, comprising: two coaxial
cables as defined in one of claims 1, 18 and 34; and an optical
fiber in communication with the coaxial cable, wherein together the
coaxial cable and the optical fiber define a transmission path.
51. The HFC network defined in claim 50, wherein the optical fiber
has a zero dispersion wavelength of about 1310 nm, a loss at 1385
nm that is less than its loss at 1310 nm and a chromatic dispersion
of between 1.5 and 8.0 ps/nm-km in the 1.4 .mu.m wavelength
region.
52. The HFC network defined in claim 50, further comprising a
multiplexer in communication with the optical fiber.
53. The HFC network defined in claim 50, further comprising a
wave-division multiplexer in communication with the optical
fiber.
54. The HFC network defined in claim 50, wherein the optical fiber
extends at least 10 kilometers along the travel path.
55. A hybrid fiber cable (HFC) network, comprising: two coaxial
cables as defined in one of claims 1, 18 and 34; and an optical
fiber in communication with the coaxial cable, wherein together the
coaxial cable and the optical fiber define a transmission path, and
wherein the optical fiber is in communication with the coaxial
cables at a node.
56. The HFC network defined in claim 50, wherein the coaxial cable
is a nominal 75 ohm coaxial cable.
Description
RELATED APPLICATIONS
[0001] This application is a continuation-in-part of U.S.
application Ser. No. 10/192,215, filed Jul. 10, 2002, the
disclosure of which is hereby incorporated herein in its
entirety.
FIELD OF THE INVENTION
[0002] The present invention is directed generally to coaxial
cables, and more specifically to coaxial cables with high
bandwidth.
BACKGROUND OF THE INVENTION
[0003] A coaxial cable is typically an excellent medium for
transmitting video and data signals because it can resist
electromagnetic interference (EMI) and can support high bandwidth
transmissions. Coaxial cables commonly used today for transmission
of RF signals, such as television signals, for example, typically
include a core containing an inner conductor and a metallic sheath
surrounding the core and serving as an outer conductor. A
dielectric material surrounds the inner conductor and electrically
insulates it from the surrounding metallic sheath. In some types of
coaxial cables, air is used as the dielectric material, and
electrically insulating spacers are provided at spaced locations
throughout the length of the cable for holding the inner conductor
coaxially within the surrounding sheath. In other known coaxial
cable constructions, an expanded foamed polymeric dielectric
surrounds the inner conductor and fills the spaces between the
inner conductor and the surrounding metallic sheath.
[0004] One important attribute of coaxial cable is its ability to
propagate a signal with as little attenuation as possible. One
method of measuring signal propagation is expressed as a percentage
of the speed of light, commonly known as velocity of propagation
(V.sub.P). Coaxial cables of the "air dielectric" type of
construction have very good signal propagation characteristics,
with V.sub.P values typically 90% or higher. However, these coaxial
cables unfortunately have relatively limited bending
characteristics and are typically susceptible to buckling,
flattening or collapsing of the outer sheath, which may adversely
affect the electrical properties of the cable and/or render it
unusable. Consequently, air dielectric type coaxial cables
typically require very careful handling during installation to
avoid such damage. Additionally, they may not be recommended for
use in installations requiring small radius bends or frequent
reverse bends. Note that they typically have structural return loss
(SRL) peaks corresponding to the disk separation distance (the
disks being included along the length of the cable to support the
conductor within the shield), which is usually designed to be above
the standard operating bandwidth (i.e., greater than 1 GHz).
Extended frequencies beyond 1 GHz can cause the disk spacing to
become much closer, thus increasing V.sub.p, attenuation, and
cost.
[0005] Coaxial cables of the "foam dielectric" type of
construction, on the other hand, ordinarily possess significantly
better bending properties than air dielectric cables. They can be
more easily installed without undue concern over buckling,
flattening or collapsing of the outer sheath and they can be used
in environments where air dielectric type cables are unsuitable.
However, they can be hampered by a somewhat lower velocity of
propagation than air dielectric type cables. This reduction in VP
and increase in attenuation loss may be attributable to the foam
dielectric.
[0006] In addition, foam dielectric cables typically present more
difficulties with attachment of the cable to connectors and
couplings. "Connectorization" can be important to the operator
making the connection, as on some occasions the connection process
may be carried out in inconvenient locations (e.g., under a house
or while perched on a telephone pole or the like). Ordinarily,
prior to fitting a cable to a connector, a short length of the
dielectric material is removed from the end of the cable with a
coring tool, which leaves the core and shield of the cable free to
contact and connect to the connector or coupling. It is important
to remove a sufficient amount of the dielectric material from the
core and sheath (i.e., leaving little to no dielectric material
remaining) so that the electrical connection between the cable and
the connector is sound. In most instances, the dielectric material
is bonded to the core and sheath with an adhesive, which can
further complicate the coring process.
[0007] Other properties of coaxial cable that can be important to
performance of the cable include usability across a wide bandwidth
spectrum (at least 1.0 GHz, and perhaps as much as 5.0 GHz), good
return loss characteristics (for example, at least -20 db, and
preferably at least -30 db), flexibility, ruggedness and/or
durability relative to the surrounding environment, and
manufacturability. In particular, it would be desirable for a
coaxial cable to have a wide usable bandwidth spectrum with
acceptable attenuation characteristics that has a nominal 75.OMEGA.
impedance (which is commonly used when attenuation characteristics
are of primary concern) or 50.OMEGA. impedance (which is typically
used when power transfer is of primary concern), and which meets at
least some of the other performance characteristics of
interest.
SUMMARY OF THE INVENTION
[0008] In view of the foregoing, the present invention is directed
to a coaxial cable that can address some of these issues. As a
first aspect, embodiments of the invention are directed to a
coaxial cable comprising: a metallic inner conductor formed of a
first material and having a first thickness; a dielectric layer
circumferentially surrounding the inner conductor formed of a
second material and having a second thickness; a metallic outer
conductor circumferentially surrounding the dielectric layer formed
of a third material and having a third thickness; and a polymeric
jacket circumferentially surrounding the outer conductor formed of
a fourth material and having a fourth thickness. A least one of the
first material, first thickness, second material, second thickness,
third material, third thickness, fourth material and fourth
thickness is selected so that the cable has: a usable bandwidth
between about 5 MHz and the cut-off frequency of the cable; a
minimum bend radius of less than about 5 times the jacket outer
diameter; and a velocity of propagation of greater than about 88
percent.
[0009] As a second aspect, embodiments of the invention are
directed to a coaxial cable comprising: a metallic inner conductor
formed of a first material and having a first thickness; a
dielectric layer circumferentially surrounding the inner conductor
formed of a second material and having a second thickness; a
metallic outer conductor circumferentially surrounding the
dielectric layer formed of a third material and having a third
thickness; and a polymeric jacket circumferentially surrounding the
outer conductor formed of a fourth material and having a fourth
thickness. A least one of the first material, first thickness,
second material, second thickness, third material, third thickness,
fourth material and fourth thickness is selected so that the
dielectric layer can be cored from the cable with a standard coring
tool such that less than a 360 degree residue remains on the inner
surface of the metallic shield and so that the cable has: a usable
bandwidth between about 5 MHz and the cut-off frequency of the
cable; and a minimum bend radius of less than 5 times the jacket
outer diameter.
[0010] As a third aspect, embodiments of the invention are directed
to a coaxial cable comprising: a metallic inner conductor formed of
a first material and having a first thickness; a dielectric layer
circumferentially surrounding the inner conductor formed of a
second material and having a second thickness; a metallic outer
conductor circumferentially surrounding the dielectric layer formed
of a third material and having a third thickness; and a polymeric
jacket circumferentially surrounding the outer conductor formed of
a fourth material and having a fourth thickness. A least one of the
first material, first thickness, second material, second thickness,
third material, third thickness, fourth material and fourth
thickness is selected so that the dielectric layer can be cored
from the cable with a standard coring tool such that less than a
360 degree residue remains on the inner surface of the metallic
shield and so that the cable has: a usable bandwidth between about
5 MHz and the cut-off frequency of the cable; and a velocity of
propagation of greater than about 88 percent.
[0011] As a fourth aspect, embodiments of the invention are
directed to a hybrid fiber cable (HFC) network, comprising any
coaxial cable as described above and an optical fiber in
communication with the coaxial cable to define a transmission path.
In some embodiments, the optical fiber has a zero dispersion
wavelength of about 1310 nm, a loss at 1385 nm that is less than
its loss at 1310 nm and a chromatic dispersion of between 1.5 and
8.0 ps/nm-km in the 1.4 .mu.m wavelength region, and in other
embodiments a multiplexer is in communication with the optical
fiber.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] FIG. 1 is a cutaway perspective view of a coaxial cable of
the present invention.
[0013] FIG. 2 is a section view of the coaxial cable of FIG. 1.
[0014] FIG. 3 is a schematic view of a hybrid fiber-cable network
of the present invention.
DETAILED DESCRIPTION OF THE INVENTION
[0015] The present invention now will be described more fully
hereinafter with reference to the accompanying drawings, in which
preferred embodiments of the invention are shown. This invention
may, however, be embodied in many different forms and should not be
construed as limited to the embodiments set forth herein. Instead,
these embodiments are provided so that this disclosure will be
thorough and complete, and will fully convey the scope of the
invention to those skilled in the art. It will be understood that
when an element (e.g., coaxial cable or cable jacket) is referred
to as being "connected to" another element, it can be directly
connected to the other element or intervening elements may also be
present. In contrast, when an element is referred to as being
"directly connected to" another element, there are no intervening
elements present. Like numbers refer to like elements throughout.
Some dimensions and thicknesses may be exaggerated for clarity.
[0016] Referring now to the drawings, a coaxial cable, designated
broadly at 20, is illustrated in FIGS. 1 and 2. The coaxial cable
20 includes a central inner conductor 22, a dielectric layer 24, an
outer conductor 26, and an outer jacket 28. These components are
described in detail below.
[0017] The conductor 22 is typically formed of solid wire. It can
be formed of any material that can conduct an electrical signal,
but is preferably formed of solid copper, copper-clad aluminum
(CCA) or copper-clad steel (CCS), with any of these materials being
optionally plated with tin, silver or gold. Such plating can reduce
the resistance of the inner conductor 22. In some embodiments,
tempering of the copper, aluminum or steel under specific
conditions during their formation can be carried out to enhance
performance and/or impact conductivity. Also, when copper is
employed as either the core material or as a cladding material, it
may be preferred to use so-called "oxygen-free" copper, which is a
commercially pure, high conductivity copper that has been produced
in such a manner that it contains virtually no oxides or residual
deoxidants.
[0018] It is preferred that the inner conductor 22 have a diameter
or thickness of between about 0.022 and 0.710 inches. Typically,
the inner conductor diameter will vary depending on the desired
impedance rating (e.g., a nominal 50.OMEGA. or 75.OMEGA. cable,
which typically carries a tolerance of .+-.2.OMEGA.), the
dielectric constant of the dielectric layer 24, and the overall
size and/or attenuation desired in the cable 20. As an example, for
a 50.OMEGA. cable that employs foamed polyethylene as the
dielectric material and an outer conductor diameter of 0.540 inch,
the diameter of the inner conductor may be about 0.201 inch. Other
impedance levels for the same outer conductor diameter can be
achieved with other combinations of inner conductor size and
materials of construction (for 75.OMEGA. cable examples, see
Examples supra). Typically, signal attenuation can be reduced in a
coaxial cable by proportionally increasing the size of the inner
and outer conductors 22, 26 (assuming constant properties of the
dielectric layer 24).
[0019] The dielectric layer 24 circumferentially surrounds the
inner conductor 22. The dielectric layer 24 is typically formed of
a low dielectric loss polymeric material, such as polyethylene or
fluorinated polyethylene, with foamed versions of these materials
being preferred. In some embodiments, a mixture of high and low
density polyethylene (for example, in a 75:25 or 85:15 mixture) may
be employed. In particular, it is preferred that the material
provide a low dissipation factor (such as 0.0001) to the cable 20;
such is characteristic of certain polyethylene materials that are
largely free of contaminants and that have relatively uniform
polymer chain lengths. The material comprising the dielectric layer
24 will typically include additives, such as antioxidants and other
stabilizers, that can maintain the integrity of the polymer over
time.
[0020] The dielectric layer 24 typically has a thickness of between
about 0.100 and 1.95 inches and a ratio of its thickness to the
diameter of the inner conductor 22 of between about 2 and 4,
depending on the desired characteristic impedance. The dielectric
layer 24 may also have a density gradient about its cross-section
(either gradually or as a "step" change) in which the density
increases with radial distance from the inner conductor 22. This
configuration, which can improve the outer support of the
dielectric layer 24 and, in turn, the bending properties of the
coaxial cable 20, is described in U.S. Pat. Nos. 6,037,545 to Fox
et al. and 5,959,245 and 6,137,058 to Moe et al., the disclosures
of which are hereby incorporated herein in their entireties. This
gradient can be achieved though a two-step extrusion process with
two different materials, or can be formed in a single step by
"overfoaming" the layer 24 and collapsing the peripheral regions of
the foam or by other methods known in this art.
[0021] If, as described above, a foamed polymeric material is
employed in the dielectric layer 24, it may be formed in a manner
that produces an expanded cell foam. This expansion of cell size
(which can cause the foam to have a lower density, with
accompanying dielectric behavior improvement, that more closely
resembles that of air while retaining the structural advantages of
foam) can be achieved by including nucleating agents (i.e.,
components that cause foaming in polymeric pellets) that have been
subjected to little or no heat history (for example, the nucleating
agent may be protected with a thermoplastic resin binder and
applied as a coating to the polymeric pellets). Alternatively,
foaming may be carried out through the injection of nitrogen or
another gas into the molten polymer at high pressure; when the
polymer is extruded, foaming occurs after the release of the
pressure. Exemplary nucleating agents and foaming procedures are
described in Fox et al., supra, and need not be described in detail
herein.
[0022] The dielectric layer 24 is typically secured to the inner
conductor 22 with an adhesive (not shown), as the inclusion of an
adhesive can improve the bending characteristics of the cable 20.
The dielectric layer 24 may be extruded directly onto the conductor
22, or may be formed separately and adhered in a subsequent step.
The adhesive should be selected to provide a uniform bonding layer
between the conductor 22 and the dielectric layer 24, and is
typically applied in as thin a layer as possible. In some
embodiments, it is desirable that the adhesive preferentially
adhere to the dielectric layer 24 and release the conductor 22 (for
example, this characteristic may improve the coring process during
attachment of the cable 20 to a connector--such adhesives are
generally termed as "controlled" adhesives, as opposed to
"aggressive" adhesives, which are not intended to release
preferentially). Controlled formulations may be diluted in a
solvent (such as water or an organic or polymeric solvent) to as 10
percent by weight or lower; aggressive adhesives may have no
solvent or may be diluted to a much lesser degree (for example, 25
or 50 percent). Some formulations may include blocking agents, like
waxes or oils, that can assist with release properties.
[0023] The adhesive may be applied as a "precoat" on the conductor
22 or applied separately before or during the addition of the
dielectric layer 24. Exemplary adhesives include low density
polyethylene, ethylene acrylic acid (EAA) and ethylene
methylacrylate (EMA) and mixtures and formulations thereof.
[0024] The shield 26 circumferentially surrounds the dielectric
layer 24 and is formed of a conductive material, which may be the
same as or different from that of the inner conductor 22. Exemplary
conductive materials include aluminum and copper (either bare,
tinned, silvered, or, in the case of aluminum, plated with copper).
The outer conductor 26 may be in solid tube, welded tube, foil or
braided form, or in combinations of these forms, although for high
performance cables solid tube or welded tube shields are preferred.
In foil form, the outer conductor 26 may comprise thin sheets of
conductive material bonded to opposite sides of a polypropylene or
polyester tape, or may comprise a solid layer. In braided form, the
outer conductor 26 comprises flexible wire woven or spirally served
around the dielectric layer 24. Irrespective of its configuration,
the outer conductor 26 should have good elongation and fatigue life
to enable it to withstand repeated bending. Tempering and other
processing steps in the manufacture of the material of the outer
conductor 26 can improve and/or enhance these characteristics.
[0025] In some embodiments, the outer conductor 26 is attached to
the dielectric layer 24 with an adhesive (not shown), which can
improve the bending properties of the cable 20. Exemplary adhesives
include EAA, EMA and mixtures and formulations thereof. The
adhesive may be applied via co-extrusion with the dielectric layer
24 or may be applied separately. To improve the coring process, it
may be preferable for the adhesive to preferentially bond to the
dielectric layer 24 and release from the outer conductor 26.
[0026] The outer conductor 26 typically has a thickness of between
about 0.006 and 0.040 inches. In some embodiments the outer
conductor 26 is constructed so that its ratio of wall thickness to
total diameter (the T/D ratio) is less than about 2.5 percent.
[0027] The outer conductor 26 is typically applied to the
dielectric layer 24 through one of two application processes:
swaging and/or welding. In the welding process, a thin flat sheet
of shielding material is bent into a cylinder and welded at the
resulting seam. In the swaging process, a tubular blank of
conducting material is extruded to a length somewhat shorter than
the length of cable desired. The blank is pulled in its axial
direction to cause it to lengthen; in doing so, its diameter
shrinks, such that the resulting outer conductor fits snugly onto
the dielectric layer 24. In some embodiments, a welded outer
conductor will undergo a swaging step in order to fit the outer
conductor 26 onto the dielectric layer 24.
[0028] In some cable embodiments, an additional corrosion-resistant
layer may be present between the outer conductor 26 and the jacket
28, particularly when the cable 20 is to be buried in use (this is
typically tested with an industry-standard salt fog test under
ASTM-B117 and SCTE IPS TP-017). The corrosion-resistant material
may take the form of a tar or flowable gel (often termed a
"floodant"), or may comprise a dry material. Dry
corrosion-resistant materials may be preferred in some embodiments
in that they may permit the jacket 28 to be bonded to the outer
conductor 26, which bonding can improve bending and flexural
properties of the cable 20, eliminate concerns with messy
floodants, and enable the cable 20 to be used in multiple
installation situations (e.g., direct buried, aerial, duct, and the
like). Exemplary dry corrosion-resistant materials include
sulphonate salts, carboxylate salts, amine salts, silicates, and
phosphates.
[0029] The jacket 28 circumferentially surrounds the outer
conductor 26 and is typically formed of a polymeric material, which
may be the same as or different from that of the dielectric layer
24. Exemplary materials include polyvinylidene fluoride,
polyethylene, polyvinylchloride, and copolymers and blends thereof.
The jacket 28 should be formed of a material that can protect the
internal components from external elements (such as water, dirt,
dust and fire) and from physical abuse. The material of the jacket
28 may include additives, such as carbon black, which can provide
UV resistance. Ordinarily, the jacket 28 has a thickness of between
about 0.020 and 0.070 inches. In some embodiments, the jacket 28 is
bonded to the outer conductor 26 with an adhesive (not shown);
exemplary adhesives are as described above.
[0030] The materials and dimensions thereof should be selected so
as to provide the cable 20 with desired high-performance
properties. For example, the cable 20 may have a usable bandwidth,
or even a continuous usable bandwidth, from about 5.0 MHz to at
least 1.0 GHz, 3.0 GHz, 3.5 GHz, 4.0 GHz, 4.5 GHz, 5.0 GHz, or even
up to the theoretical cut-off frequency of the cable 20 (as
measured by Equation 1 below)
Freq.sub.cutoff=7.51 V.sub.p/(D+d) (Equation 1)
[0031] wherein Freq.sub.cutoff is the cut-off frequency, Vp is the
velocity of propagation, D is the inner diameter of the outer
conductor, and d is the outer diameter of the center conductor.
[0032] This usable bandwidth may be continuous or may have some
attenuation spikes at certain frequencies of transmission. The
cable 20 may also have a return loss of -15 db, -20 db, -25 db, -30
db, -45 db or more. The cable 20 may have a nominal impedance of
50.OMEGA. (preferred for power transfer performance), 75.OMEGA.
(preferred for attenuation performance) or some other desired
impedance level. The cable 20 may also have a velocity of
propagation (V.sub.P) of 88 percent, or even 90 percent or more, as
measured by ASTM 4566-1.
[0033] Mechanically, the cable 20 may have very desirable
performance properties. For example, the cable 20 may have a
minimum bend radius (as measured by SCTE IPS TP-108) that is less
than about 10 times the outer diameter of the jacket 28, and in
some embodiments less than 5 times the jacket outer diameter. As
another example, the cable 20 may exhibit improved reverse bend
performance (as measured by repeatedly bending the cable over a
mandrel having a radius of twenty times the diameter of the outer
conductor of the cable), such that it may endure 5 to 100 cycles
prior to failure (failure being defined as buckling or ovality of
the cable 20; see CommScope, Inc. HFC Upgrade Manual, Volume 1,
Coax (1998). The cable 20 may also exhibit improved cyclic or
expansion loop fatigue resistance (as measured by fatiguing the
cable by expansion loop fatigue testing described in Improved Plant
Life through Longer Lasting Trunk and Distribution Cable, available
at www.nadrew.com), such that it can withstand 5,000 to over 20,000
cycles prior to failure.
[0034] The cable 20 may also be configured such that it
"connectorizes" suitably. For example, the materials of the cable
20 (and in particular the materials of the dielectric material and
the adhesives attaching the dielectric layer 24 to the core 22 and
outer conductor 26) may be selected such that, when a conventional
coring tool is employed on the cable 20, less than a 360 degree
residue of dielectric material remains on the inner surface of the
outer conductor 26. In some embodiments, it is preferred that no
residue remain on the inner surface of the outer conductor 26 in
the cored region. Conventional coring tools are exemplified by
Lemco XQ 715, available from Lemco Tool Corporation, Cogan Station,
Pa., Cablematic QRT 715, available from Ripley Co., Cromwell,
Conn., and CablePrep SCT 715QR, available from CablePrep, Chester,
Conn., and their configurations and use will be understood by those
skilled in this art.
[0035] The cable 20 may be employed in a variety of applications,
particularly those that can benefit from a high performance cable.
Exemplary applications for the cable 20 include cable television
cables, security cameras and video devices, video-on demand
devices, high-speed Internet access systems, high frequency
satellite transmission and reception devices, data communication
systems, computer networks, and residential telecommunication
systems. The cable 20 may also be used in hybrid fiber cable (HFC)
networks in conjunction with optical fiber, particularly optical
fiber using dense wavelength division multiplexing (DWDM) and/or
zero water peak (ZWP) or low water peak (LWP) enhanced fiber
systems. For descriptions of exemplary optical fibers and HFC
networks, see U.S. Pat. No. 6,205,268 to Chraplyvy et al. and
co-pending and co-assigned U.S. patent application Ser. No.
10/192,215, filed Jul. 25, 2000, the disclosures of each of which
are hereby incorporated by reference herein.
[0036] In some embodiments, the cable 20 may have a length of no
more than about 150 feet; in such embodiments, the structural
return loss characteristics of the cable 20 may be less stringent
(for example, about -15 db) than with other applications because of
the relatively short signal path. The cable 20 may also be
constructed in standardized lengths (e.g., 1000 feet) or in a
customized length as desired.
[0037] When constructed as described, a cable 20 of the present
invention can provide the user a variety of premium physical and
electrical properties. As such, a single cable type can be employed
in different applications. For example, if the desired electrical
and mechanical properties are present in a single cable 20, it can
be used in buried, aerial and duct applications, each of which have
different performance requirements (as an example, a buried cable
needs corrosion-resistance, whereas a duct cable likely would not,
but needs flexibility in order to be strung through ductwork that
may change direction sharply). The use of a single cable type can
simplify construction of a cable network, as often two or more of
these types of applications will be present within the same
network. Use of a single cable type reduces the amount of matching
of cable performance that might otherwise be necessary.
[0038] Referring now to FIG. 3, a communications system, designated
broadly at 200, is illustrated therein. The communications system
200 includes one or more transmitters 202 and one or more receivers
204 that are interconnected with an HFC network 210. The HFC
network 210 includes an optical fiber portion 212 that includes
optical fiber, preferably of the type described above, and a
coaxial cable portion 214 that includes coaxial cable as described
above. In the illustrated system 200, the optical fiber portion 212
is connected to the transmitter 202 and travels to a node 216
located near the receiver 204, where the signal is converted from
an optical signal to an electrical signal by techniques known to
those skilled in this art. The coaxial cable portion 214 travels
from the node 216 to the receiver 204.
[0039] The optical fiber portion 212, although illustrated as a
single transmission line, more typically includes a number of
discrete optical fiber lengths that travel either (a) from the
transmitter 202 to an intermediate node or hub, (b) between
intermediate nodes or hubs, or (c) from an intermediate node or hub
to the node 216. The presence of the intermediate nodes can provide
significant flexibility to the system for operation, maintenance,
modification, and enhancement. It will also be understood by those
skilled in this art that other components, such as amplifiers,
multiplexers, demultiplexers, wave-division multiplexers and
demultiplexers, splitters, and the like may also be included in the
optical fiber portion 212. It should also be noted that, although
only a single transmitter 202 is illustrated herein, in many
embodiments multiple transmitters 202 will feed signals into the
HFC network 210. Also, in some embodiments a single transmitter 202
may feed multiple signals into the optical fiber portion 212, or
may feed a signal of multiple bandwidths into the optical fiber
portion 212.
[0040] In traveling from the node 216 to the receiver 204, the
coaxial cable portion 214 typically has a relatively short travel
path (ordinarily on the order of 1,000 to 6,000 feet); for example,
it may only travel from a central location within a neighborhood.
It should be noted that, although only a single coaxial cable
portion 214 is illustrated herein, in many embodiments multiple
coaxial cable portions will extend from the node 216 to multiple
receivers 204, and that multiple receivers 204 may also receive
signals from a common coaxial cable portion 214.
[0041] Exemplary devices that may serve as transmitters 202 include
broadband video devices, cable television devices and modems,
telephony devices, data distribution devices, Internet servers, and
the like. Exemplary devices that may serve as receivers 204 include
the types of devices that would typically receive signals from
these transmitters, including televisions, cable television boxes
and modems, telephones, wireless networks, personal computers,
handheld devices, interactive gaming devices, and the like. It
should also be understood that, although the transmitters 202 is
illustrated as a transmitter and the receiver 204 described as
receivers, signals can be processed in either direction between the
transmitter 202 and the receiver 204.
[0042] The invention will be described in greater detail in the
following non-limiting examples.
EXAMPLE 1
[0043] A cable can be constructed according to the parameters set
forth in Table 1.
1 TABLE 1 Component Material Size (in.) Conductor CCA 0.166 OD
Dielectric Layer 85% HDPE/15% LDPE 0.686 OD density .ltoreq. 0.215
g/cc Adhesive Aggressive Shield Aluminum 0.715 OD Jacket MDPE and
carbon black 0.785 OD
[0044] This cable has the following properties set forth in Table
2.
2 TABLE 2 Property Value Nominal Impedance 75 .OMEGA. .+-. 2
.OMEGA. Attenuation 1.52 db/100 ft @ 1 GHz Reverse Bending 69
cycles to failure Minimum Bend Radius 5 in. Cyclic Expansion Loop
Fatigue 23,500 cycles Velocity of Propagation 89 percent
EXAMPLE 2
[0045] A cable can be constructed according to the parameters set
forth in Table 3.
3 TABLE 3 Component Material Size (in.) Conductor CCA 0.166 OD
Insulator 85% HDPE/15% LDPE 0.686 OD density .ltoreq. 0.215 g/cc
Adhesive Controlled Shield Aluminum 0.715 OD Jacket MDPE and carbon
black 0.785 OD
[0046] This cable has the following properties set forth in Table
4.
4 TABLE 4 Property Value Nominal Impedance 75 .OMEGA. .+-. 2
.OMEGA. Reverse Bending 69 cycles Minimum Bend Radius Approximately
3 in. Cyclic expansion Loop Fatigue 23,500 cycles Coring Cored
cleanly Velocity of Propagation 89 percent
EXAMPLE 3
[0047] A cable can be constructed according to the parameters set
forth in Table 5.
5 TABLE 5 Component Material Size (in.) Conductor CCA 0.166 OD
Insulator 85% HDPE/15% LDPE 0.686 OD density .ltoreq. 0.215 g/cc
Adhesive Controlled Shield Aluminum 0.715 OD Jacket MDPE and carbon
black 0.785 OD
[0048] This cable has the following properties set forth in Table
6.
6 TABLE 6 Property Value Nominal Impedance 75 .OMEGA. .+-. 2
.OMEGA. Attenuation 1.52 db/100 ft @ 1 GHz Coring Cored cleanly
Velocity of Propagation 89 percent
[0049] The foregoing is illustrative of the present invention and
is not to be construed as limiting thereof. Although a few
exemplary embodiments of this invention have been described, those
skilled in the art will readily appreciate that many modifications
are possible in the exemplary embodiments without materially
departing from the novel teachings and advantages of this
invention. Accordingly, all such modifications are intended to be
included within the scope of this invention as defined in the
claims. The invention is defined by the following claims, with
equivalents of the claims to be included therein.
* * * * *
References