U.S. patent application number 10/972920 was filed with the patent office on 2005-03-10 for terminal assembly for a coaxial cable.
This patent application is currently assigned to DELPHI TECHNOLOGIES, INC.. Invention is credited to Gladd, Joseph Howard, Hickox, Jeffrey Michael, Ketterer, William C..
Application Number | 20050054237 10/972920 |
Document ID | / |
Family ID | 33158660 |
Filed Date | 2005-03-10 |
United States Patent
Application |
20050054237 |
Kind Code |
A1 |
Gladd, Joseph Howard ; et
al. |
March 10, 2005 |
Terminal assembly for a coaxial cable
Abstract
A terminal for a coaxial cable includes an electrically
conductive core mounted in a dielectric member. The dielectric
member along with the conductive core are positioned within an
electrically conductive ground shield. The ground shield includes
two identical split-barrel housing members which are joined
together. When joined, the housing members form a cylindrical
channel having surfaces which intimately contact an exposed length
of cable outer conductor layer, creating a conductive connection
between the outer conductor layer and the ground shield and
structurally maintaining the outer conductor layer concentric to
the dielectric sheath and inner conductor of the cable.
Inventors: |
Gladd, Joseph Howard;
(Cortland, OH) ; Hickox, Jeffrey Michael;
(Middlefield, OH) ; Ketterer, William C.; (Girard,
OH) |
Correspondence
Address: |
David P. Wood
DELPHI TECHNOLOGIES, INC.
Mail Code: 480-410-202
P.O. Box 5052
Troy
MI
48007-5052
US
|
Assignee: |
DELPHI TECHNOLOGIES, INC.
|
Family ID: |
33158660 |
Appl. No.: |
10/972920 |
Filed: |
October 25, 2004 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
10972920 |
Oct 25, 2004 |
|
|
|
10414165 |
Apr 15, 2003 |
|
|
|
6809265 |
|
|
|
|
Current U.S.
Class: |
439/578 |
Current CPC
Class: |
H01R 13/5045 20130101;
H01R 9/0524 20130101; H01R 4/023 20130101; H02G 15/085
20130101 |
Class at
Publication: |
439/578 |
International
Class: |
H01R 004/26 |
Claims
1. A terminal for an end of a coaxial cable, said coaxial cable
including an inner conductor, an inner dielectric sheath around
said inner conductor, an outer conductor layer having a cylindrical
outer surface and concentrically surrounding said inner dielectric
sheath and inner conductor, and an outer dielectric sheath around
said outer conductor, and in which said coaxial cable end has been
stripped back to expose a tip of said inner conductor, an axial
length of said inner dielectric sheath, and an axial length of said
outer conductor layer outer surface, said terminal comprising: an
electrically conductive core conductor for electrically connecting
with said inner conductor of said coaxial cable; a dielectric
member having a body for receipt therein of said core conductor,
wherein said dielectric member comprises a material comparable to
said inner dielectric sheath; a ground shield comprising first and
second electrically conductive housing members, each said housing
member including a channel comprising a substantially half
cylindrical surface intimately matching the shape of the exposed
length of outer surface of said cable outer conductor layer,
wherein each of said housing members also includes first and second
mating, integral attachment members capable of being joined
together to thereby form said channels into a complete cylinder,
whereby, when said ground shield housing members are joined
together, said channel surfaces intimately contact said exposed
length of outer conductor layer, creating a conductive connection
between said outer conductor layer and said ground shield and
structurally maintaining said outer conductor layer concentric to
said dielectric sheath and said inner conductor.
2. The terminal of claim 1, further comprising a conductive bonding
agent disposed between said ground shield and said exposed length
of outer conductor layer, wherein said conductive bonding agent
comprises epoxy.
3. A ground shield for an end of a coaxial cable, said coaxial
cable including an inner conductor, an inner dielectric sheath
around said inner conductor, an outer conductor layer having a
cylindrical outer surface and concentrically surrounding said inner
dielectric sheath and inner conductor, and an outer dielectric
sheath around said outer conductor, and in which said coaxial cable
end has been stripped back to expose an axial length of said outer
conductor layer outer surface, said ground shield comprising: first
and second electrically conductive, rigid ground shield housing
members, each said housing member including a channel comprising a
substantially half cylindrical surface intimately matching the
shape of the exposed length of outer surface of said cable outer
conductor layer, said housing members capable of being joined
together to thereby form said channels into a complete cylinder,
whereby, when said ground shield housing members are joined
together, said channel surfaces intimately contact said exposed
length of outer conductor layer, creating a conductive connection
between said outer conductor layer and said ground shield and
structurally maintaining said outer conductor layer concentric to
said dielectric sheath and said inner conductor, wherein said rigid
ground shield housing members comprises a nickel plated zinc alloy.
Description
TECHNICAL FIELD
[0001] The present invention relates to electrical terminals for
connection to coaxial cable and more particularly relates to a
terminal having a two-piece ground shield.
BACKGROUND OF THE INVENTION
[0002] A typical coaxial cable for signal transmission includes a
center conductive core or inner conductor surrounded by an inner
dielectric sheath. An outer conductor or conductive shield
surrounds the inner dielectric sheath and typically is a metal
braid. The conductive shield is surrounded by an outer dielectric
sheath of the cable.
[0003] Electrical terminals are known for terminating a coaxial
cable so that the cable can be connected to another connecting
device, such as a complementary mating connector, a printed circuit
board, and the like. Such terminals typically include a core
conductor or contact for mechanically and electrically connecting
to an end of the inner conductor of the cable, a dielectric sleeve
therearound, and an outer conductor or ground shield for
mechanically and electrically connecting to the outer conductor of
the cable.
[0004] The terminal must be configured and connected to the coaxial
cable in such a manner as to minimize voltage standing wave ratio
(VSWR), insertion losses, and radio frequency (RF) leakage.
Commonly, the largest component of insertion loss is reflection due
to impedance discontinuities. Energy reflected at impedance
discontinuities does not reach the load. Such discontinuities
result from variations in the radial distance between the outer
surface of the inner conductor and the inner surface of the outer
conductor. Such discontinuities include changes in diameter in
either conductor or deformation of either conductor. RF leakage
results from radiation loss through holes or seams in the terminal
or cable.
[0005] Electrical and mechanical connection of the core conductor
of the terminal to the inner conductor of the cable is commonly
established by axially inserting the inner conductor into the core
conductor and then radially crimping and/or soldering the core
conductor of the terminal to the inner conductor of the cable. It
is also common for such electrical and mechanical connection of the
ground shield to the outer conductor of the cable to be established
by a method that includes stripping the end of the coaxial cable,
sliding a ferrule onto the cable, folding the outer conductor
braiding back over the outer dielectric sheath, inserting the
stripped end of the coaxial cable into the ground shield, unfolding
the braiding over the ground shield, sliding the ferrule over the
braiding and ground shield, then crimping the ferrule to the
braiding thereby pressing the braiding against the ground
shield.
[0006] U.S. Pat. No. 3,854,003 to Duret discloses a ground shield
terminal assembly comprising two elastic half-shell conductive
housing members having chamfered ends. The assembled housing
members are surrounded by a threaded metallic sleeve which enables
a nut to cooperate with the threads to press a ring having an
inclined surface over the chamfered ends to deform the housing
members, thereby pressing them against the outer conductor of a
coaxial cable.
[0007] Such known methods for assembling a terminal to a coaxial
cable are labor intensive and technique sensitive. These methods
require significant manual manipulation of the shielding braid
which deforms the outer conductor causing reflection and insertion
loss. Crimping also deforms the outer conductor causing reflection
and insertion loss. Variation in assembly technique impacts the
integrity of the connection and results in variation in
performance.
[0008] Known coaxial cable connectors commonly include a threaded,
cylindrical ground shield which has an axially extending bore.
These known ground shields commonly include plating on outside
surfaces and on inside surfaces which define the bore. It is
difficult to apply a uniform plating to inside surfaces of such a
design. Plating voids thereby result which increase reflection and
leakage losses.
[0009] As the use of high frequency systems such as digital
satellite radio, Global Positioning Systems (GPS), cell phones, and
mobile television continues to grow there is an increasing need for
coaxial cable connectors which meet the radio frequency performance
needs of such systems, offer consistent performance, and are easy
and inexpensive to assemble.
SUMMARY OF THE INVENTION
[0010] The present invention provides advantages and alternatives
over the prior art by providing a terminal for connection to a
coaxial cable, together with a ground shield and a method for
assembling the ground shield to a coaxial cable. The terminal
comprises a two-piece ground shield capable of being connected to
an outer conductor of the cable without the need to deform the
outer conductor either by dressing it over the ground shield or by
crimping it to the ground shield. Importantly, the terminal is
capable of being used to carry high frequency signals such as those
used by communication and entertainment systems in automotive and
other applications.
[0011] According to a preferred embodiment of the present invention
disclosed herein, a terminal assembly for a coaxial cable is
provided which includes a ground shield with surfaces defining an
internal passageway. In the preferred embodiment, the ground shield
includes a strain relief portion having protruding ribs for
engaging an outer dielectric sheath of the coaxial cable and a
contact portion for electrically and mechanically bonding an outer
conductor of the coaxial cable to the ground shield. As a result,
it is not necessary to crimp the outer conductor to the ground
shield.
[0012] In the preferred embodiment, the ground shield is comprised
of two identical shield halves joined at a plane extending along an
axis of the internal passageway. Each of the shield halves is
constructed using a die cast process enabling strain relief
features, internal component retention features, and shapes that
optimize radio frequency performance to be easily produced. The
two-piece design enables the ground shield to have a uniform
plating. Each of the shield halves is easier to reliably plate than
a complete shield having a bore.
[0013] A method is provided for assembling the ground shield of the
present invention to a coaxial cable. The method enables automated
assembly of the ground shield to the cable.
[0014] These and other features and advantages of the present
invention will become apparent from the following brief description
of the drawings, detailed description, and appended drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0015] The present invention will now be described, by way of
example, with reference to the accompanying drawings, in which:
[0016] FIG. 1 is an exploded perspective view of a preferred
embodiment of a terminal according to the present invention;
[0017] FIG. 2 is a side elevation view of a coaxial cable with
various internal layers exposed;
[0018] FIG. 3 is a perspective view of the terminal of FIG. 1;
[0019] FIG. 4 is a view taken along line 4-4 of FIG. 3;
[0020] FIG. 5 is a flow diagram of a method of the present
invention; and
[0021] FIG. 6 is an exploded perspective view an aspect of the
terminal of FIG. 1, but with a cable in place to illustrate the
elements identified in FIG. 5.
DETAILED DESCRIPTION OF THE INVENTION
[0022] Referring to the figures wherein like numerals refer to like
elements throughout the several views, FIGS. 1, 3, and 4 illustrate
a preferred embodiment of an electrical terminal 10 of the present
invention. The terminal 10 includes an electrically conductive core
conductor 12, a dielectric member 14, a conductive ground shield
16, and a split ring support 18. The ground shield 16 is an
assembly of two identical ground shield halves or housing members
20a, 20b. When joined, the ground shield housing members 20a, 20b
define the completed ground shield 16. Each ground shield housing
member 20a, 20b is preferably a rigid die cast member constructed
of a nickel plated zinc alloy.
[0023] FIG. 2 illustrates a coaxial cable 200 which includes an
inner conductor 202, an inner dielectric sheath 204 around the
inner conductor 202, an outer conductor layer 206 having a
cylindrical outer surface and concentrically surrounding the inner
dielectric sheath 204 and the inner conductor 202, and an outer
dielectric sheath 208 around the outer conductor layer 206. The
coaxial cable 200 is shown stripped back with an exposed tip of the
inner conductor 202, an exposed axial length of the inner
dielectric sheath 204, and an exposed axial length of the outer
conductor layer 206.
[0024] Referring back to FIGS. 1, 3, and 4, the core conductor 12
includes a body portion 30 and a contact portion 32. Preferably,
the core conductor 12 is formed from sheet metal which is
preferably gold plated brass which is stamped and then rolled to
form the generally cylindrical shape of the core conductor 12. The
contact portion 32 includes two spring members 34 which extend from
the body portion 30 and terminate at distal ends 36. The spring
members 34 have opposing surfaces which define a pin-receiving bore
38. The body portion 30 includes an inner surface which defines an
inner conductor receiving bore 40.
[0025] The dielectric member 14 has a generally cylindrical shape
and is preferably made of Teflon or a material comparable to the
inner dielectric sheath 204. An inner surface 50 of the dielectric
member 14 defines an axially extending bore 52. The inner surface
50 includes a first portion 54 for containing the body portion 30
of the core conductor 12. An annular gap 118 extends between the
first portion 54 of the inner surface 50 of the dielectric member
14 and body portion 30 of the core conductor 12 to allow room for
protrusions (not shown) in the body portion 30 caused by crimping.
The inner surface 50 also includes a second portion 56 for
retaining the contact portion 32 of the core conductor 12. The
inner surface 50 further includes a third portion 57 which
surrounds the spring members 34 of the core conductor 12. The inner
surface 50 of the dielectric member 14 holds the core conductor 12
in axial alignment within the terminal 10. The dielectric member 14
further includes an outer surface 58. The outer surface 58 includes
a large diameter portion 60, a reduced diameter portion 62, and a
transition portion 64 therebetween. The outer surface 58 also
includes an annular groove 66.
[0026] The ground shield 16 includes an inner surface 70 and an
outer surface 72. The inner surface 70 defines an axially extending
passageway 74. The ground shield 16 includes a rearward strain
relief portion 76 for contact with the outer dielectric sheath 208
of the coaxial cable 200, a contact portion 78 for electrical
connection with the outer conductor layer 206 of the coaxial cable
200, a support portion 80 which retains the dielectric member 14,
and a forward mating portion 82 for connection with a complementary
ground of a mating connector (not shown). Each of the two ground
shield housing members 20a, 20b generally have a split barrel shape
and are aligned along a plane P of separation running parallel to a
longitudinal axis A of the ground shield 16. The ground shield 16
includes an enlarged rearward outer portion 84 which serves as a
processing aid. Enlarged diameter portions 86 on a mid-portion of
the outer surface 72 align with features on a complementary coaxial
cable connector housing (not shown).
[0027] The inner surface 70 of the strain relief portion 76
includes a plurality of spaced strain relief ribs 88 each extending
partially around a circumference of the inner surface 70 for
gripping the outer dielectric sheath 208 of the coaxial cable
200.
[0028] The contact portion 78 of the inner surface 70 of the ground
shield 16 is shaped to intimately match the shape of the outer
surface of the exposed length of the outer conductor layer 206.
When the ground shield housing members 20a, 20b are joined together
over the exposed length of the outer conductor layer 206, a
conductive connection is created between the ground shield 16 and
the outer conductor layer 206. The inner surface 70 of the ground
shield 16 structurally maintains the outer conductor layer 206
concentric to the dielectric sheath 204 and the inner conductor 202
without the need to deform the outer conductor layer 206 either by
dressing it over the ground shield 16, by crimping it to the ground
shield 16, or by tightening the ground shield 16 around the outer
conductor layer 206.
[0029] In the preferred embodiment, a conductive bonding agent 90
is disposed on the contact portion 78 of the inner surface 70 of
the ground shield 16 and the outer conductor layer 206 of the
coaxial cable 200. Solder is the preferred bonding agent. However,
conductive epoxy or other bonding agents may also be used. The
conductive bonding agent 90 bonds the outer conductor layer 206 to
the ground shield 16 and fills in voids and discontinuities between
the outer conductor layer 206 and the ground shield 16. The
conductive bonding agent 90 also bonds the first ground shield
housing member 20a to the second ground shield housing member 20b.
At a distal end 207 of the exposed axial length of outer conductor
206, the inner surface 70 of the ground shield transitions to a
first reduced diameter portion 91. The exposed axial length (shown
at 92) of inner dielectric 204 presses against the first reduced
diameter portion 91 of the ground shield 16 preventing the
conductive bonding agent 90 from contacting the exposed axial
length of inner conductor 202 or the core conductor 12. An aperture
94 extends through the contact portion 78 of each ground shield
housing member 20a, 20b enabling visual inspection of the
conductive bonding agent 90.
[0030] In some alternate embodiments, no conductive bonding agent
90 is used and the ground shield housing members 20a, 20b are
joined together by welding, by form fit, or by another attachment
mechanism known to those skilled in the art. Once so attached, the
inner surface 70 of the ground shield 16 intimately contacts the
exposed layer of outer conductor layer 206 providing an electrical
connection between the ground shield 16 and the outer conductor
layer 206.
[0031] The dielectric support portion 80 includes a second reduced
inner diameter portion 96 which surrounds the reduced diameter
portion 62 of the dielectric member 14. The dielectric support
portion 80 also includes an annular rib 98 on the inner surface 70
for engaging the annular groove 66 in the dielectric member 14.
[0032] The forward mating portion 82 includes four spaced contact
beams 100 which extend forwardly from the dielectric support
portion 80. Inside surfaces of the four contact beams 100 form an
opening 102 for receiving a complementary mating ground shield (not
shown). The split ring support 18 extends around the outside
surface of the contact beams 100 to provide a normal force when a
complementary ground (not shown) is mated to the ground shield
16.
[0033] Prior to assembly, each ground shield housing member 20a,
20b defines an axially extending open-ended trough or channel 104.
The channel 104 has an open side such that a cross-section of the
channel 104 forms substantially one-half of a cylindrical surface
of the passageway 74. In the preferred embodiment, each ground
shield housing member 20a, 20b includes a coating 106 of the
conductive bonding agent 90 disposed on the channel 104 surface in
an area that forms the contact portion 78 of the completed ground
shell 16. The coating 106 is preferably a solder paste.
Alternately, other conductive coatings or claddings can be used.
Each ground shield housing member 20a, 20b can also be provided
without a coating 106 or cladding.
[0034] Each of the ground shield housing members 20a, 20b include
mateable, integral attachment members which include a protruding
rail 108 and a complementary slot 110 which extend longitudinally
along opposing edges 112, 114 of each ground shield housing member
20a, 20b. When the housing members 20a, 20b are assembled into the
completed ground shield 16, the rail 108 and the slot 110 are
positioned such that the rail 108 on each ground shield housing
member 20a, 20b is received in the slot 110 of the other ground
shield housing member 20b, 20a. In the preferred embodiment, a
notched portion 116 of channel 104 provides room for a braiding of
the outer conductor layer 206 to fan out. This helps to prevent a
loose braiding strand from lodging between the two ground shield
housing members 20a, 20b.
[0035] FIGS. 1, 3, and 4 illustrate a female configuration of the
terminal 10 of the present invention. Male configurations of the
terminal of the present invention may also be produced in a manner
well known to those skilled in the art.
[0036] Referring now to FIG. 5, a flowchart 300 illustrates a
preferred embodiment of a method for electrically connecting the
ground shield 16 to the coaxial cable 200. FIG. 6 illustrates the
terminal 10 along with the coaxial cable 200 to depict the elements
identified in the flowchart of FIG. 5. Referring back to FIG. 5, in
step 302 the coaxial cable 200 is provided including an inner
conductor 202, an inner dielectric sheath 204 around said inner
conductor 202, an outer conductor layer 206 having a cylindrical
outer surface and concentrically surrounding said inner dielectric
sheath 204 and inner conductor 202, and an outer dielectric sheath
208 around said outer conductor 206.
[0037] In step 304, an end portion 210 of the coaxial cable 200 is
stripped leaving an exposed tip of inner conductor 202, an exposed
axial length of inner dielectric 204, and an exposed axial length
of outer conductor layer 206. Optionally, the end portion 210 of
the coaxial cable 200 may be stripped without leaving the exposed
axial length of inner dielectric 204. However, it is preferable to
have an exposed axial length of inner dielectric 204 to prevent the
conductive bonding agent 90 from contacting the exposed inner
conductor 202.
[0038] In step 306, the conductive ground shield 16 is provided,
the ground shield 16 includes the first housing member 20a and the
second housing member 20b, each of the housing members 20a, 20b
includes a channel 104 defined by a substantially half cylindrical
surface having a contact portion 78 which intimately matches the
shape of the exposed axial length of the outer conductor layer 206,
each of the housing members 20a, 20b also include mating, integral
attachment members capable of being joined together to form the
channels 104 into a complete cylinder. Preferably, the mating
integral attachment member includes the protruding rail 108 and the
complementary slot 110 which extend longitudinally along the
opposing edges 112, 114 of each ground shield housing member 20a,
20b. Each rail 108 fits closely within a respective slot 110. The
channel 104 of each housing member 20a, 20b may also include the
coating 106 of conductive bonding agent 90 provided in the contact
portion 78 of each of the housing members 20a, 20b.
[0039] In step 308, the end portion of the coaxial cable 200 is
placed into the channel 104 of the first housing member 20a,
aligning the exposed axial length of the outer conductor layer 206
with the contact portion 78.
[0040] Then, in step 310, the second housing member 20b is placed
in contact with the first housing member 20a mating the integral
attachment members which preferably include the rail 108 and the
complementary slot 110. The channels 104 thereby form a cylinder
surrounding and electrically contacting the exposed axial length of
outer conductor layer 206. The contact portion 78 of the second
housing member 20b aligns with the exposed axial length of the
outer conductor layer 206. In a preferred embodiment of the method,
the coating 106 of the conductive bonding agent 90 is provided in
the contact portion 78 of each of the housing members 20a, 20b, and
the conductive bonding agent 90 is heated until it flows between
the housing members 20a, 20b forming a both a mechanical bond
between the housing members 20a, 20b and the conductor layer 206
between when the conductive bonding agent 90 cools. Bonding agent
90 can also flow into the seam between the housing members 20a and
20b and directly mechanically bond them together. Also in the
preferred embodiment of the method, the conductive bonding agent 90
is heated in the same heating step until it flows between the
housing members 20a, 20b and the outer conductor layer 206 forming
a conductive bond between the housing members 20a, 20b and the
outer conductor layer 206 when the conductive bonding agent cools.
In an alternate embodiment, each of the housing members 20a, 20b
are provided with corresponding form fit features, and the two
housing members 20a, 20b are mechanically attached by pressing the
two housing members 20a, 20b together. In another alternate
embodiment, the two housing members 20a, 20b are attached using a
welding process. In yet another alternate embodiment, a bonding
agent such as solder is injected into the passageway 74 or
otherwise applied to the housing members 20a, 20b to bond them
together.
[0041] This invention has been described with reference to a
preferred embodiment and modifications thereto. Further
modifications and alterations may occur to others upon reading and
understanding the specification. It is intended to include all such
modifications and alterations insofar as they come within the scope
of the invention.
* * * * *