1. Field of the Invention
This invention relates to electrical cable connectors. More particularly, the invention relates to a flat inner conductor coaxial connector with improved passive intermodulation distortion (PIM) electrical performance and mechanical interconnection characteristics.
2. Description of Related Art
Coaxial cable connectors are used, for example, in communication systems requiring a high level of precision and reliability.
During systems installation, rotational forces may be applied to the installed connector, for example as the attached coaxial cable is routed towards the next interconnection, maneuvered into position and/or curved for alignment with cable supports and/or retaining hangers. Rotation of the coaxial cable and coaxial connector with respect to each other may damage the connector, the cable and/or the integrity of the cable/connector inter-connection. Further, once installed, twisting, bending and/or vibration applied to the interconnection over time may degrade the connector to cable interconnection and/or introduce PIM.
PIM is a form of electrical interference/signal transmission degradation that may occur with less than symmetrical interconnections and/or as electro-mechanical interconnections shift or degrade over time, for example due to mechanical stress, vibration, thermal cycling, oxidation formation and/or material degradation. PIM is an important interconnection quality characteristic, as PIM from a single low quality interconnection may degrade the electrical performance of an entire Radio Frequency (RF) system.
Prior coaxial cables typically have a coaxial configuration with a circular outer conductor evenly spaced away from a circular inner conductor by a dielectric support such as polyethylene foam or the like. The electrical properties of the dielectric support and spacing between the inner and outer conductor define a characteristic impedance of the coaxial cable. Circumferential uniformity of the spacing between the inner and outer conductor prevents introduction of impedance discontinuities into the coaxial cable that would otherwise degrade electrical performance.
A stripline is a flat conductor sandwiched between parallel interconnected ground planes. Striplines have the advantage of being non-dispersive and may be utilized for transmitting high frequency RF signals. Striplines may be cost effectively generated using printed circuit board technology or the like. However, striplines may be expensive to manufacture in longer lengths/larger dimensions. Further, where a solid stacked printed circuit board type stripline structure is not utilized, the conductor sandwich is generally not self supporting and/or aligning, compared to a coaxial cable, and as such may require significant additional support/reinforcing structure.
Competition within the RF cable industry has focused attention upon reducing materials and manufacturing costs, electrical characteristic uniformity, defect reduction and overall improved manufacturing quality control.
Therefore, it is an object of the invention to provide a coaxial cable and method of manufacture that overcomes deficiencies in such prior art.
The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and, together with a general description of the invention given above, and the detailed description of the embodiments given below, serve to explain the principles of the invention.
The inventors have recognized that the prior accepted coaxial cable design paradigm of concentric circular cross section design geometries results in unnecessarily large coaxial cables with reduced bend radius, excess metal material costs and/or significant additional manufacturing process requirements.
The inventors have further recognized that the application of a flat inner conductor, compared to conventional circular inner conductor configurations, enables precision tunable capacitive coupling for the elimination of PIM from inner conductor connector interface interconnections.
An exemplary stripline RF transmission cable 1 is demonstrated in
The dimensions/curvature of the edge sections 20 may be selected, for example, for ease of manufacture. Preferably, the edge sections 20 and any transition thereto from the top and bottom sections 10, 15 is generally smooth, without sharp angles or edges. As best shown in
The desired spacing between the inner conductor 5 and the outer conductor 25 may be obtained with high levels of precision via application of a uniformly dimensioned spacer structure with dielectric properties, referred to as the dielectric layer 30, and then surrounding the dielectric layer 30 with the outer conductor 25. Thereby, the cable 1 may be provided in essentially unlimited continuous lengths with a uniform cross section at any point along the cable 1.
The inner conductor 5 metallic strip may be formed as solid rolled metal material such as copper, aluminum, steel or the like. For additional strength and/or cost efficiency, the inner conductor 5 may be provided as copper coated aluminum or copper coated steel.
Alternatively, the inner conductor 5 may be provided as a substrate 40 such as a polymer and/or fiber strip that is metal coated or metalized, for example as shown in
The dielectric layer 30 may be applied as a continuous wall of plastic dielectric material around the outer surface of the inner conductor 5. The dielectric layer 30 may be a low loss dielectric formed of a suitable plastic such as polyethylene, polypropylene, and/or polystyrene. The dielectric material may be of an expanded cellular foam composition, and in particular, a closed cell foam composition for resistance to moisture transmission. Any cells of the cellular foam composition may be uniform in size. One suitable foam dielectric material is an expanded high density polyethylene polymer as disclosed in commonly owned U.S. Pat. No. 4,104,481, titled “Coaxial Cable with Improved Properties and Process of Making Same” by Wilkenloh et al, issued Aug. 1, 1978, hereby incorporated by reference in the entirety. Additionally, expanded blends of high and low density polyethylene may be applied as the foam dielectric.
Although the dielectric layer 30 generally consists of a uniform layer of foam material, the dielectric layer 30 can have a gradient or graduated density varied across the dielectric layer 30 cross section such that the density of the dielectric increases and/or decreases radially from the inner conductor 5 to the outer diameter of the dielectric layer 30, either in a continuous or a step-wise fashion. Alternatively, the dielectric layer 30 may be applied in a sandwich configuration as two or more separate layers together forming the entirety of the dielectric layer 30 surrounding the inner conductor 5.
The dielectric layer 30 may be bonded to the inner conductor 5 by a thin layer of adhesive. Additionally, a thin solid polymer layer and another thin adhesive layer may be present, protecting the outer surface of the inner conductor 5 for example as it is collected on reels during cable manufacture processing.
The outer conductor 25 is electrically continuous, entirely surrounding the circumference of the dielectric layer 30 to eliminate radiation and/or entry of interfering electrical signals. The outer conductor 25 may be a solid material such as aluminum or copper material sealed around the dielectric layer as a contiguous portion by seam welding or the like. Alternatively, helical wrapped and/or overlapping folded configurations utilizing, for example, metal foil and/or braided type outer conductor 25 may also be utilized.
If desired, a protective jacket 35 of polymer materials such as polyethylene, polyvinyl chloride, polyurethane and/or rubbers may be applied to the outer diameter of the outer conductor. The jacket 35 may comprise laminated multiple jacket layers to improve toughness, strippability, burn resistance, the reduction of smoke generation, ultraviolet and weatherability resistance, protection against rodent gnaw through, strength resistance, chemical resistance and/or cut-through resistance.
The flattened characteristic of the cable 1 has inherent bend radius advantages. As best shown in
Electrical modeling of stripline-type RF cable structures with top and bottom sections with a width similar to that of the inner conductor (as shown in
To obtain the materials and structural benefits of the stripline RF transmission cable 1 as described herein, the electric field strength and corresponding current density may be balanced by increasing the current density proximate the mid-section 7 of the inner conductor 5. The current density may be balanced, for example by modifying the dielectric constant of the dielectric layer 30 to provide an average dielectric constant that is lower between the inner conductor edges 3 and the respective adjacent edge sections 20 than between a mid-section 7 of the inner conductor 5 and the top and the bottom sections 10, 15. Thereby, the resulting current density may be adjusted to be more evenly distributed across the cable cross section to reduce attenuation.
The dielectric layer 30 may be formed with layers of, for example expanded open and/or closed cell foam, dielectric material where the different layers of the dielectric material have a varied dielectric constant. The differential between dielectric constants and the amount of space within the dielectric layer 30 allocated to each type of material may be utilized to obtain the desired average dielectric constant of the dielectric layer 30 in each region of the cross section of the cable 1.
The materials selected for the dielectric layer 30, in addition to providing varying dielectric constants for tuning the dielectric layer cross section dielectric profile for attenuation reduction, may also be selected to enhance structural characteristics of the resulting cable 1.
Alternatively and/or additionally, the electric field strength and corresponding current density may also be balanced by adjusting the distance between the outer conductor 25 and the mid-section 7 of the inner conductor 5. For example as shown in
A capacitivly coupled flat conductor connector 43 for terminating a flat inner conductor stripline RF transmission cable 1 is demonstrated in
As best shown in
A “molecular bond” as utilized herein is defined as an interconnection in which the bonding interface between two elements utilizes exchange, intermingling, fusion or the like of material from each of two elements bonded together. The exchange, intermingling, fusion or the like of material from each of two elements generates an interface layer where the comingled materials combine into a composite material comprising material from each of the two elements being bonded together.
One skilled in the art will recognize that a molecular bond may be generated by application of heat sufficient to melt the bonding surfaces of each of two elements to be bonded together, such that the interface layer becomes molten and the two melted surfaces exchange material with one another. Then, the two elements are retained stationary with respect to one another, until the molten interface layer cools enough to solidify.
The resulting interconnection is contiguous across the interface layer, eliminating interconnection quality and/or degradation issues such as material creep, oxidation, galvanic corrosion, moisture infiltration and/or interconnection surface shift.
The inner conductor 5 extends through the bore 45 for capacitive coupling with a mating conductor 55, such as an inner conductor trace on a printed circuit board 60, supported by a female connector body 65. Because the inner conductor 5 and mating conductor 55 are generally flat, the capacitive coupling between the inner conductor 5 and the mating conductor 55 is between two planar surfaces. Thereby, alignment and spacing to obtain the desired level of capacitive coupling may be obtained by adjusting the overlap and/or offset between the capacitive coupled surfaces.
As best shown in
Where the inner conductor 5 and the mating conductor 55 are retained parallel to and aligned one above the other with respect to width, the surface area between the capacitivly coupled surfaces is determined by the amount of longitudinal overlap applied between the two. With the offset provided as a constant (the thickness of the selected spacer 70), the overlap may be adjusted to tune the capacitive coupling for a desired frequency band of the RF signals to be transmitted along the cable 1.
Precision alignment of the inner conductor 5 and the mating conductor 55 may be facilitated by an alignment insert 75, for example as shown in
The alignment between the alignment insert 75 and the alignment receptacle 77 may be further enhanced by applying the ramp surface 79 and angled groove 81 to both sides of the alignment insert 75 and alignment receptacle 77, as best shown in
As best shown in
The conductor seat 87 may also be used as a guide for cable end preparation. By test fitting the alignment insert 75 against the male connector body 50 with the inner conductor 5 extending over the conductor seat 87, the connector end of the conductor seat 87 demonstrates the required trim point along the inner conductor 5 for correct fit of the inner conductor 5 into the conductor seat 87 and thereby the length of the inner conductor 5 necessary to obtain the desired overlap.
Application of a transverse trough 89 at the connector end of the conductor seat 87, as best shown in
As best shown in
One skilled in the art will appreciate that, because the overlap may be defined by the conductor seat 87 dimensions, the capacitive coupling may be quickly precision tuned for a range of different frequency bands by selection between a plurality of alignment inserts 75, each of the alignment inserts 75 provided with conductor seats 87 of varied longitudinal length, for example as shown in
As best shown in
One skilled in the art will appreciate that the cable 1 and capacitive coupling connector 43 provide numerous advantages over a conventional circular cross section coaxial cable and connector embodiments. Because the desired inner conductor surface area is obtained in the cable 1 without applying a solid or hollow tubular inner conductor, a metal material reduction of one half or more may be obtained. Further, the flat inner conductor 5 configuration enables a direct transition to planar elements, such as traces on printed circuit boards and/or antennas. The capacitive coupling connector 43 may eliminate PIM with respect to the inner conductor 5 and is easily assembled for operation with a range of different frequency bands via simple exchange of the alignment insert 75.
Where in the foregoing description reference has been made to ratios, integers or components having known equivalents then such equivalents are herein incorporated as if individually set forth.
While the present invention has been illustrated by the description of the embodiments thereof, and while the embodiments have been described in considerable detail, it is not the intention of the applicant to restrict or in any way limit the scope of the appended claims to such detail. Additional advantages and modifications will readily appear to those skilled in the art. Therefore, the invention in its broader aspects is not limited to the specific details, representative apparatus, methods, and illustrative examples shown and described. Accordingly, departures may be made from such details without departure from the spirit or scope of applicant's general inventive concept. Further, it is to be appreciated that improvements and/or modifications may be made thereto without departing from the scope or spirit of the present invention as defined by the following claims.
This application is a continuation-in-part of commonly owned co-pending U.S. Utility patent application Ser. No. 13/240,344, titled “Connector and Coaxial Cable with Molecular Bond Interconnection” filed Sep. 22, 2011 by Kendrick Van Swearingen and James P. Fleming, hereby incorporated by reference in its entirety, which is a continuation-in-part of commonly owned co-pending U.S. Utility patent application Ser. No. 12/951,558, titled “Laser Weld Coaxial Connector and Interconnection Method”, filed Nov. 22, 2010 by Ronald A. Vaccaro, Kendrick Van Swearingen, James P. Fleming, James J. Wlos and Nahid Islam, hereby incorporated by reference in its entirety. This application is also a continuation-in-part of commonly owned co-pending U.S. Utility patent application Ser. No. 13/294,586, titled “Tabbed Connector Interface” filed 11 Nov. 2011 by Kendrick Van Swearingen, hereby incorporated by reference in its entirety. This application is also a continuation-in-part of commonly owned co-pending U.S. Utility patent application Ser. No. 13/208,443, titled “Stripline RF Transmission Cable” filed 12 Aug. 2011 by Frank A. Harwath, hereby incorporated by reference in its entirety. This application is also a continuation-in-part of commonly owned co-pending U.S. Utility patent application Ser. No. 13/427,313, titled “Low Attenuation Stripline RF Transmission Cable” filed 22 Mar. 2012 by Frank A. Harwath, hereby incorporated by reference in its entirety, which is a continuation-in-part of U.S. Utility patent application Ser. No. 13/208,443.
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Parent | 13427313 | Mar 2012 | US |
Child | 13571073 | US | |
Parent | 13208443 | Aug 2011 | US |
Child | 13427313 | US | |
Parent | 13240344 | Sep 2011 | US |
Child | 13208443 | US | |
Parent | 12951558 | Nov 2010 | US |
Child | 13240344 | US | |
Parent | 13571073 | US | |
Child | 13240344 | US | |
Parent | 13294586 | Nov 2011 | US |
Child | 13571073 | US |