US3055967A - Coaxial cable with low effective dielectric constant and process of manufacture - Google Patents

Description

Sept. 25, 1962 A. BONDON 3,055,967 COAXIAL CABLE WITH LOW EFFECTIVE DIELECTRIC CONSTANT AND PROCESS OF MANUFACTURE Filed May 29, 1961 INVENTOR LEWIS A. BONDON w n Q 2413} A ORNEYS United States Patent Ofiice 3,055,967 Patented Sept. 25, 1962 COAXIAL CABLE WITH LOW EFFECTIV E DIELECTRIC CONSTANT AND PROCESS OF MANUFACTURE Lewis A. Bondon, 90 Yantacaw Brook Road, Upper Montclair, NJ. Filed May 29, 1961, Ser. No. 113,540 6 Claims. (Cl. 174-28) The present invention relates to high frequency coaxial cable and particularly such cable having a very low effective dielectric constant. The present invention also relates to a method of manufacture of coaxial cable, particularly adapted to the coaxial cable of the present invention.

It is contemplated that the present invention will find greatest application in the field of radio frequency coaxial cables and accordingly the features of the present invention will be discussed primarily with reference to this application. It should be understood, however, that the use of the present invention is not limited to radio frequency cables but that the present invention may be applied to other uses in the electrical art.

This application is a continuation-in-part of my related copending application Serial No. 730,345 for Insulated Electrical Conductor and Method of Manufacture, filed April 23, 1958, now Patent 2,998,472, issued August 29, 1961.

Many types of radio frequency cables of the coaxial type are known in the art. A basic problem exists with regard to these coaxial cables which has heretofore escaped satisfactory solution. Such cables have two conductors, an outer conductor generally of annular crosssection and an inner conductor having a common center. that is coaxial with the outer conductor. The spacing between these conductors and the electrical properties of the intermediate material between these conductors has a profound influence upon the electrical characteristics of the cable. It is therefore necessary to support these conductors in such a way that they remain concentric and at the same time utilize the optimum electrical properties of the material in the space between the inner and outer conductors. In the normal case the most desired property for the intermediate material is a lowest dielectric constant. The lowest dielectric constants obtainable are those of a vacuum, air or other gases.

From the foregoing explanation it will be seen that to outer conductors; while to obtain the desired structural properties and thus maintain concentricity, a strong and continuous supporting structure should be provided.

The best solid dielectrics have substantially higher dielectric constants than that of air and other gases and thus produce inferior attenuation properties. so the use of solid dielectrics does not completely solve the structural problem. monly manufactured by extrusion and in the process of extruding the center conductor within the core of solid material it is exceedingly difiicult to maintain the center conductor properly located in the center of the core of dielectric material and in random contact with the dielectric.

A different approach to this problem has been to minimize the supporting structure and to fill the intermediate space between conductors with air or another gas. For example, beads of glass or ceramic material have been utilized in spaced positions along the cable center conductor to support the center conductor within the outer conductor. Helical type supports consisting of a spiraled plastic supporting structure wound on the center con ductor have also been utilized.

Such structures, particularly when bent, often allow the center conductor to move from its concentric position; furthermore, in the case of beads, these are often broken if the cable is bent in the wrong place. All supporting structures in which the supporting elements are spaced periodically along the length of the cable are inclined to have an undesirable frequency sensitivity due to the fact that the frequency response of the cable is affected when the length of spacing between supporting elements correlates with the Wavelength of a radio frequency signal in the operating frequency range of the cable.

Insulated electrical conductors according to the present invention utilize an array of insulating tubes laid about a conductor and pressed into uniform and continuous contact with it to form a symmetrical array wherein the insulating crosssection provides a maximal amount of air space and a minimal amount of dielectric mass. At the same time a high degree of structural integrity is provided so that the resulting arrangement provides the best physical features of solid dielectric while approaching the air dielectric construction optimum electrical properties.

The present invention provides an improvement over the insulated electrical conductor configuration disclosed in my prior copending application Serial No. 730,345, now Patent 2,998,472 issued August 29, 1961, in that portions of the insulating tubes are eliminated in order that the critical volume adjacent to the center conductor be occupied by a higher proportion of air. Thus the effective dielectric constant of the coaxial cable is improved but the physical characteristics of the cable may be maintained substantially unimpaired.

Insulated electrical conductors according to the present invention can be fabricated by a method herein disclosed which is of remarkable simplicity and thereby greatly reduces the labor cost of producing electrical conductors over that of more complicated production methods. The method which will be disclosed hereinafter is also capable of being practiced with very little specially constructed apparatus. For the most part, only simple, well known types of cable-assembly and tube-drawing apparatus are required.

A preferred method of manufacture as later described in more detail consists primarily in assembling insulating tubing having notches in at least one side of each tube and a conductor element in a loose array generally corresponding to the desired final configuration and inserting the insulating tubing and conductors into a length of hard jacket while maintaining the general configuration of the array. Therefore the jacket of metal, organic material or other semi-rigid material, is drawn or otherwise reduced in size with respect to the cross-section of the tubing, or the tubing enlarged radially beyond its dimension at insertion, to cause the insulating tubes and c0nductors to be tightly packed into an array of the desired configuration. As a result the insulating tubing and the conductor or conductors are immovably secured within tubing adjacent the conductor so that a low effective dielectric constant is obtained.

Accordingly, in addition to providing the above described features and advantages, it is an object of the present invention to provide a coaxial cable in which a center conductor is secured within an outer jacket by reason of its placement in a con-figuration of notched insulating tubes which are arranged in a tightly packed array within the jacket with the notches in the insulating tubes adjacent the center conductor.

It is still another object of the present invention to provide a method of fabricating coaxial cables of the above and similar types which is simple in operation, requires a minimum of labor and principally involves the use of only simple conventional cable-assembling and tube-drawing apparatus, together with simple notch cutting apparatus for notching the insulating tubes.

Further objects and advantages will be apparent from a consideration of the following explanation in conjunc tion with the appended drawings, in which:

FIGURE 1 is a perspective cutaway view of a coaxial cable according to the present invention;

FIGURE 2 is a transverse cross-sectional view of the coaxial cable of FIG. 1;

FIGURE 3 is a transverse cross-sectional view of the coaxial cable of FIGS. 1 and 2 as it would appear during the course of manufacture;

FIGURE 4 is a partially cut-away plan view of the coaxial cable of FIGS. 1 and 2;

FIGURE 5 is a sectional partially schematic view of apparatus for assembling the component elements of the cable of FIGS. l-4; and

FIGURE 6 is a sectional view taken in FIG. 5.

Referring now to the drawings, FIG. 1 shows an insulated electrical conductor in the form of a coaxial cable 11. The cable is formed with an external jacket 12 of conductive material such as aluminum or copper alloys. It is preferred that the jacket 12 be of a high-conductivity semi-rigid material, i.e. material often referred to in the trade as semi-flexible and which may be bent and re-formed without deformation or loss of electrical and mechanical advantages. The aluminum tubing of FIG. 1 is merely exemplary and the jacket could be formed of other metals or organic or other materials. Furthermore, the jacket 12 need not be in the form of tubing. It may, for example, be a wound armored type covering such as that utilized in the familiar BX cable, or round wire or hat wire braiding.

concentrically located within the jacket 12 is a center conductor 13. The center conductor 13 may be formed of copper or any other suitable conducting material such as aluminum. The center conductor 13 is shown to be solid in the cable illustrated in FIG. 1; however, the center conductor 13 may be hollow and in some cases this will be desirable to produce a saving of material and weight. The center conductor 13 is rigidly secured within the jacket 12 due to its placement within an array of tubes 14 of non-conducting or insulating material. In FIG. 1 the tubes 14 are formed with relatively thin walls so that the volume between the center conductor 13 and the outer jacket v12 is filled primarily with air or such other 'gas as may be placed within the jacket 12.

It may be noted that the tubes 14 within the jacket 12 are not circular in shape. This is most readily apparent in FIG. 2. In some cases it might be desirable to form the tubes 14 in a non-circular shape but in the device shown in FIGS. 1 and 2, it is contemplated that the tubes 14 would originally be formed in circular shape and that they together with the center conductor 13 would be placed within the jacket 12 and forceably deformed to the shape shown in FIG. 2. It should further be understood that throughout the specification and claims the word tube is to be construed to include both filled and unfilled tubes and elongated rods whether they behollow or not. For example, cellular rods of foamed plastic or elastomeric material may be used, such as foam rubber, foamed polyethylenes and polyurethanes.

It will be noted, particularly in FIGS. 1 and 4, that the tubes 14 are provided with notches illustrated as triangular in form. As a result approximately one-half of the material of the tubes 14 which would be immediately adjacent the center conductor 13 in the absence of the notches is removed and effectively replaced by gaseous dielectric. Since gaseous dielectric has a substantially lower dielectric constant than the best available solid along lines 66 material for tubes 14, the effective dielectric constant of the cable 11 is substantially improved by provision of the notches 15. The improvement in dielectric constant is substantially greater than would be expected from the amount of material removed due to the fact that the electric field is stronger in the vicinity of the center conductor and thus removal of material from the volume immediately surrounding the center conductor provides a proportionately larger decrease in effective dielectric constant. For example, a material which would provide an effective dielectric constant of 2.3 if extruded or otherwise placed in the cable to completely fill the space between center conductor and jacket may be expected to provide an effective dielectric constant of approximately 1.45 were it to be used in a construction having tubular insulating members without notches. If the tubular insulating members are then provided with notches according to the present invention, a further improvement may be expected to a value of effective dielectric constant of approximately 1.3. The significance of the difference between an effective dielectric constant of 1.3 as compared with an effective dielectric constant of 1.45 is better realized when it is pointed out that the value of 1.45 is 50% farther removed from the optimum value of 1.00 than is the value of approximately 1.30 provided by the present invention.

The coaxial type insulated electrical conductor of FIGS. 1 and 2 is normally used for the transmission of radio frequency electrical energy and in such a case the sizes of the outer conductor or jacket 12 and the inner conductor 13 are of importance in determining the electrical characteristics of the coaxial cable. Also the properties of the material placed between the cent-er conductor 13 and the jacket 12 are of importance in determining the electrical properties of the cable. To a lesser extent the properties of the conductive materials of which the jacket 12 and the center 13 are formed are also important.

The manner in which the various characteristics of the cable such as cut-off frequency, power handling capability, attenuation, characteristic impedance, etc. are controlled by the dimensions and materials of the various elements is well known in the art and will not be discussed here. It will suffice to say that where the cable is to be used for the transmission of radio frequency energy it is generally desirable to provide as low an effective dielectric constant in the space between the inner conductor and the outer conductor as is possible. This is best accomplished by providing the maximum air space or gas space in this area.

When the cable of FIG. 1 is designed for 50 ohms characteristic impedance, a cable of inch nominal outside diameter may be constructed to give a nominal cutoif frequency of 15 kmc./s.; /2 inch O.D. to give 10 krnc./ s. nominal cutoff; /3 inch CD. to give 5000 mc./ s. nominal cutoff, and 1 /3 inch 0D. to give 2800' mc./s. nominal cutoff.

Polyethylene or tetrafluoroethylene polymer, (a product sold under the trade-mark Teflon), tubes may be utilized in the construction of the above described devices. It is obviously desirable to utilize a material for the tubes 14 (where they are to be used in radio frequency transmission cable) which has a minimum dielectric constant while still having sufficient physical strength and other necessary properties. As previously mentioned the tubes 14 may be either hollow, as would usually be the case for radio frequency energy transmission, or in some cases they may be solid. Many diverse types of insulating material can be utilized for the tubes 14 such as natural or synthetic rubber, neoprene, copolymers of butadiene and styrene or acrylonitrile, polyisobutylene, isoprene, polystyrene and vinyl compounds such as polymers and copolymers of vinyl chloride, vinyl acetate and vinylidene compounds. In addition the tubes can be made of reinforced material. For example the tubing can be made of glass fibers impregnated o-r reinforced with any of the above mentioned materials and additionally containing silicone or reinforcing silicone rubber.

Although various advantages and features of the insulated electrical conductors according to the present invention have been previously mentioned in general, pa-rticular advantages of the embodiment of FIGS. 1 and 2 are now explained in more detail.

It will be noted that notches 15 extend to only a limited extent into tubes 14 so that the virtual wall described above is maintained intact and the notches 15 provide access only to the interior of tubes 14 which is still separated -from the jacket 12 by the outer wall of tubes 14. In the event that tubes 14 are made solid rather than hollow, notches such as 15 need not necessarily be limited to one side of the tube 14 so long as a smooth surface is provided or other suitable means along the sides of the insulating tubes 14 where they are in mutual contact to avoid the existence of an air gap between jacket 12 and CI1ta conductor '13.

It will be noted that in the embodiment of FIGS. l-4 there is an uncut section of tube between each adjacent pair of notches 15 which is almost equal to one-half of the pitch or the distance between notches. This distance can be reduced until the notches are virtually adjacent at the outer surface of the tube and the integrity of the tube is maintained by the inner part of the tube wall.

While there will obviously be more or less weakening of the tubes 14 by virtue of the notches 15, this will in general not be critical and in any event can be compensated by increasing the wall thickness of tubes 14. The advantage in reduction of dielectric constant achieved by notches 15 will be far greater than any slight increase in eifective dielectric constant due to slight increase in the wall thickness of tubes 14.

Those skilled in the art will appreciate that as the frequency of transmission increases in cables, as illustrated in FIGS. l-4, the wavelength will diminish to the point where the notches 15 are no longer very small compared to a wavelength and an undesirable frequency sensitivity will be introduced. This will not affect the operation of the cable for lower radio frequencies and is not as serious as might be expected for the higher frequencies for several reasons. First, the cable has an inherent cut-off frequency, and in many cases the notches 15 can be sufliciently closely spaced so that they produce no appreciable effect below the inherent cut-off frequency of the cable. For example the effective pitch of the notches can be made substantially less than the effective spacing between the surfaces Since the notches can be quite closely spaced, for example While the notches 15 have been illustrated as triangular in section, other shapes may be preferred in particular instances and the notches could be rectangular, semicircular, or of other shape within the scope of the invention.

It should be further noted that the usual installation of cable of the type shown in FIGS. 1 and 2 requires that bends be made in the cable, and in any event, the cable is normally wound on a reel for shipping and. unwound for use at the destination. With cable accord ing to the present invention there is little or no tendency for the center conductor 13 to be dislodged from its center position in the jacket 12 and even if temporarily slightly dislodged due to coiling, it tends to be selfcentering upon reassuming a straight line. At all times, relative longitudinal movement between the inner and outer conductors is restricted to a minimum. Obviously when a metal jacket such as aluminum is utilized in a configuration such as that shown in FIGS. 1 and 2, the cable has a very high resistance to crushing due both to the strength of the jacket and also to the spoke-like array of tubes therewithin.

The cable of this invention is easily cut, dressed and handled without the necessity for special preparation or special tools. No bulky flaring tools, hot knives or irons are required as in the case of wedged or laminated membrane type supporting elements which require special treatment and handling where the outer jacket is removed.

Referring now to FIGS. 5 and 6, apparatus is shown, partially schematically, for assembling the elements of the coaxial cable to form a cable according to the present invention. In FIG. 5 reels 21 are schematically illustrated for supplying insulator tubing to be assembled into the cable. In the apparatus of FIGS. 5 and 6 it is contemplated that the tubing on reels 21 will be as yet unnotched. Reel 22 is provided to supply center conductor 13 for the assembly.

A guider 23 is provided with spaced openings 24 for insulator tubes 14 together with a central opening 25 to guide the center conductor 13. The apertures 24 for insulator tubes 14 are spaced to a substantially greater extent in guider die 23 than will be the tubes 14 when initially assembled in the jacket 12. Room is thereby provided for a cutting mechanism including a stud 26 on which there is rotatably mounted a fly cutter blade 28 integrally formed with a pulley 27.

As will be seen in FIG. 6, a belt 31 resides in a channel 29 of pulley 27 and a further pulley 30 connected to a suitable source of power (not shown) serves to drive the fly cutter blade 28.

Pitch of the notches 15 cut in tubes 14 is preferably controlled by synchronizing the speed of rotation of slide cutter blade 28 with the movement of tubes 14, for example, by synchronizing the drive pulley 30 with the pay off rate of reels 21. It will be noted that the arrangement of FIG. 5 inherently causes the notches 15 in the various tubes 14 to be staggered relative to one another, thus providing the advantage with respect to frequency sensitivity previously described. While it is assumed that frequency sensitivity is generally undesirable, it is not impossible that frequency sensitivity might be desired in special cases, in which case the notches could be arranged to provide the desired sensitivity.

The particular notching mechanism illustrated in FIG. 5 is given purely by way of example and it will be appreciated that other notching mechanisms with rotating or reciprocating cutters could be provided to carry out the method of manufacture herein described.

It should further be noted that the notches in tubes 14 need not be cut in conjunction with the assembly operation but rather may be formed by cutting or otherwise in a preliminary operation in which case the tubing would feed off of reels 21 with the notches already provided. In such a case a guiding mechanism would preferably be provided to assure that the notches 15 are placed toward the center of the cable configuration. Also metering reels having teeth mating with notches 15 may be provided and interlinked to provide any desired relative position between notches of respective ones of the tubes 14.

In the specific form of apparatus illustrated in FIG. 5, tubes 14 and center conductor 13 continue through the apparatus to a secondary guiding die 32 which causes the tubes 14 and conductor 13 to be smoothly guided into a jacket 12 which is slightly larger than the combined dimension of tubes 14 and conductor 13 (for example, by a factor of 10 to 15%). It will be appreciated that with 10 to 15% extra room within jacket 12 the tubes 14 and conductor 13 may readily be drawn into a long length of jacket 12 with comparatively little force required. The force for pulling tubes 14 and conductor 13 may be provided by a winch or any other suitable means connected to a cable 35 which may be secured by means of a clamp 34 and a woven wire harness 33 to the ends of tubes 14 and conductor 13.

By the apparatus illustrated in FIG. lengths of coaxial cable up to 1000 feet or more may be assembled without difliculty.

After the internal elements have initially been drawn into the tube jacket 12 the cross-section of the cable will appear as shown in FIG. 3. It will be noted that very little clearance and a minimum of longitudinal drag need be allowed to draw the arrayed internal elements consisting of tubes 14 and inner conductor 13 into the jacket 12. This is a particular advantage of the present arrangement which allows the cable to be fabricated by a simple procedure which does not require excessive reduction in cross-section of the outer jacket 12. The present procedure thus results in relatively little longitudinal molecular orientation or work-hardening of the metal jacket. Once the internal elements have been assembled within the outer jacket 12, the jacket 12 is reduced in diameter by drawing, roll swaging, or any suitable process to the desired diameter. Apparatus such as drawing benches and dies for reducing tubing is well known and is accordingly not illustrated. Other techniques may be used to envelop the array of tubes within the jacket, e.g. by extruding the metal of the jacket around the array as in conventional lead or aluminum press techniques.

As previously explained, FIG. 2 shows the cross-section of the elements of FIG. 3 after the jacket 12 has been reduced to the desired diameter. Although substantial deformation has been made in the tubes 14 in FIG. 2, it is obvious that a lesser amount of deformation may be made. It is only necessary that the array of insulating tubes 14 and the inner conductor 13 be securely held to retain the inner conductor 13 in position in the center of the jacket 12. Additional advantages accrue from making the insulating tubes 14 of readily deformable material in that the reduced diameter of the outer jacket is considerably less critical and any variation on the intended diameter is easily absorbed by more or less deformation of the insulating tubes 14.

From the foregoing description of the method of manufacture of the coaxial cable it will be seen that a particularly simple method is provided. A primary advantage of the method is that no particular precautions for accurate positioning of the inner conductor within its supporting elements are necessary due to the face that the inner conductor is automatically centered in its jacket 12 when the jacket is reduced due to the fact that the stresses in the various insulating tubes 14 will equalize themselves to center the inner conductor 13. This follows from the fact that the various tubes surrounding the inner conductor 13 are substantially identical and are uniform throughout their length. This is not a particularly critical condition however, and reasonable variations in the tubing 14 can be tolerated without producing an undue eccentricity of the center conductor 13.

Obviously many variations can be made in the particularly described method of manufacture. As an example the internal elements can be assembled in a desired configuration before or as they are placed in the jacket. Furthermore, an armored type jacket can be wound over the internal elements rather than compressing a solid tube jacket on the elements as desired.

Other methods may be used for contraction of the elements for placement within the jacket such as stretching or forceably elongating the non-conductive tubes to cause them to contract in effective cross-section. This is applicable in the case where they are formed of extensible material. Furthermore, in any of the suggested methods heat treatment or chemical treatment such as partial 'or complete vulcanization may be utilized to set the expandable or deformable non-conductive elements after they are properly arranged within the jacket. Other variations in the particular method described will be obvious to those in the art.

While the particular form of cable shown by way of illustration in the drawings comprises six insulating tubes 14 arranged around a center conductor 13, all of substantially equal diameter, it will be appreciated that such a configuration will provide only a limited range of outer conductor diameter to inner conductor diameter ratios. Considerably more variation in such ratios is desirable in order to provide a range of characteristic impedances for coaxial cables. This is accomplished by utilizing a greater or lesser number of insulating tubes 14 (not less than three such tubes). As a fewer number of tubes are utilized a progressively smaller diameter center conductor 13 is provided so that irrespective of the number of insulating tubes 14 the uncompressed array of insulating tubes 14 together with a central center conductor 13 forms a stable array of elements which will necessarily be deformed to symmetric configuration upon reduction in the diameter of jacket 12. To describe this relation differently it may be stated that the size of the insulating elements with respect to the conductor element is such that in the undeformed condition of the array the size of the elements is such to place each of the elements in contact with at least three other of the elements, regardless of the number of insulating tubes in the array.

The advantage of the above described size relationship resides in the fact that the ultimate configuration of the array after deformation is definitely predetermined with virtually no opportunity for the center conductor to be asymmetrically located due to accidental displacement preliminary to the compression of the jacket 12.

It should further be noted that while the illustrated embodiment of the invention shows only a single ring of insulating tubes surrounding a center conductor, two or more such rings of tubes could be provided within the scope of the invention and this expedient may also be utilized to provide different outer conductor to inner conductor diameter ratios.

From the foregoing explanation it will be seen that the present invention provides a number of types of coaxial cables which are suitable for various applications and have many advantageous features, among which are simplicity of manufacture, ready availability ofcom ponents, physical strength and superior electrical char-' acteristics, particularly low effective dielectric constant. A method of manufacture of great efficiency is also provided.

Although a number of variations and modifications to the illustrated embodiments have been suggested, it is obvious that numerous other variations of the invention may be made by those skilled in the art.

Accordingly theinvention is not to be construed to be limited to the particular embodiments shown or suggested, but is to be considered to be limited solely by the appended claims.

What is claimed is:

1. An insulated electrical conductor assembly comprising a hollow substantially cylindrical jacket and a plurality of elongated elements within said jacket, one of said elongated elements being a conductor element and at least three of which are substantially deformed non-conductive elements of normally equal circular crosssection when in undeformed condition, said non-conductive elements being formed of resiliently deformable material, said elements being placed in a tightly packed array with non-conductive elements being the outermost elements of said array and with said conductor element in the center of said array, said conductor element being surrounded by non-conductive elements having their respective surfaces in continuous intimate contact with at least two adjacent non-conductive elements thereby avoiding any internal free path between conductive components of said assembly, each said non-conductive element having a series of substantially transverse notches extending the length of said non-conductive element and located adjacent said conductor element, said jacket having an inside transverse dimension less than the maximum said array of elements in undeformed condition, and the size of said non-conductive elements being when in undeformed condition substantially the size which would place each of said elements in contact with at least three other of said elongated elements while they are in said array in undeformed condition.

2. An insulated electrical conductor assembly comprising a hollow substantially cylindrical jacket, and a plurality of elongated elements within said jacket, one of said elongated elements being a conductor element with a peripherally continuous cross-section and at least three of which are substantially deformed hollow nonconductive elements of normally equal circular crosssection when in undeformed condition, said non-conductive elements being formed of resiliently deformable material, said elements being placed in a transversely ordered tightly-packed array with non-conductive elements being the outermost elements of said array and with said conductor element in the center of said array, said conductor element being surrounded by non-conductive elements having their respective surfaces in continuous intimate contact with at least two adjacent non-conductive elements thereby avoiding any internal free path between conductive components of said assembly, each said nonconductive element having a series of substantially transverse notches extending the length of said non-conductive element and located adjacent said conductor element, said jacket having an inside transverse dimension less than the maximum transverse dimension of said array of eletransverse dimension of undeformed condition substantially the size which would place each of said elements in contact with at least three other of said elongated elements While they are in said array in undeforrned condition.

3. An assembly as claimed in claim 2, wherein the notches of each said non-conductive element are staggered in position with respect to notches of other non-conductive elements.

4. An assembly as claimed in claim 2, wherein the effective pitch of said series of notches is less than the effective spacing between the surfaces of said jacket and said conductor element.

5. The method of manufacturing a coaxial cable as sembly comprising the steps of placing a plurality of elongated elements into a hollow elongated jacket of permanently deformable material, said elongated elements including at least one conductor element and at least three substantially equal-diameter cylindrical resiliently deformable non-conductive elements, each said non-conductive element having a series of substantially transverse notches extending the length of said non-conductive element, the placing of said non-conductive elements in said jacket being with said notches of said non-conductive elements toward the center of said jacket and said conductor element arranged in the center of said non-conductive elements, said elongated elements being placed into said jacket in an array in which each elongated element may simultaneously be placed in tangential contact with at least three other elongated elements Without substantial deformation of any said elements, the inside dimension of said jacket being larger than said array of elongated elements; and progressively reducing the transverse dimension of said jacket throughout its length to cause said elongated elements progressively along the length of the jacket to be placed in a stable array of predetermined form with each of said elongated elements in tangential contact with at least three other of said elements and to cause said non-conductive elements to be deformed by the progressive reduction of said jacket dimension.

6. The method of manufacturing an insulated conductor assembly comprising the steps of guiding a plurality of elongated elements into a transversely spaced array, said elongated elements including a conductor element in the center of said array and at least three substantially equal diameter resiliently deformable non-conductive elements arranged around and spaced from said conductor element; passing said elongated elements by a cutter to cut a series of transverse notches throughout the length of said nonconductive elements, said notches being on the surface of said non-conductive elements facing said conductor element; drawing said elongated elements into a compact array maintaining the relative position of said elements and the notches thereon; placing said elongated elements into a hollow elongated jacket of permanently deformable material, said elongated elements being placed into said jacket in an array in which each elongated element may simultaneously be placed in tangential contact with at least three other elongated elements without substantial deformation of any of said elements, the inside dimension of said jacket being larger than said array of elongated elements, and progressively reducing the transverse dimension of said jacket throughout its length to cause said elongated elements progressively along the length of the jacket to be placed in a stable array of predetermined form with each of said elongated elements in tangential contact with at least three other of said elements with the notches of said non-conductive elements located adjacent said conductor element and to cause said non-conductive elements to be deformed by the progressive reduction of said jacket dimension.

References Cited in the file of this patent UNITED STATES PATENTS

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