CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is related to commonly owned prior U.S. Patent Nos. 3,797,104, naming
William T. Pote as sole inventor, and 4,758,685 naming William T. Pote and Robert
Landsman as joint inventors thererof, both of which are entitled "Flexible Coaxial
Cable and Method of Making Same," and is an improvement thereon. This application
is also related to the contemporaneously filed, commonly owned, copending U.S. Patent
Application entitled "Method of Making Flexible Coaxial Cable Having Threaded Dielectric
Core," naming William T. Pote as the sole inventor thereof, the contents of which
are specifically incorporated by reference herein in their entirety.
TECHNICAL FIELD
[0002] The present invention relates to improvements in the methods of making flexible coaxial
cables and the resultant improved cables made by such methods.
BACKGROUND ART
[0003] Coaxial cables, such as for microwave transmission, have existed in the prior art
for a considerable period of time. As technology has developed, a need for flexible
coaxial cables whose electrical characteristics do not vary during flexure of the
cable, such as in aerospace utilizations, has developed. In such utilizations, often
the electrical characteristics of the cable are critical and any variation therein
will yield unsatisfactory transmissions via such cables. In order to increase the
flexibility of prior art coaxial cables, corrugated outer conductors, such as disclosed
in U.S. Pat. Nos. 3,582,536; 3,173,990 and 2,890,263 have been utilized. In addition,
other prior art attempts of providing such flexibility have employed a corrugated
outer sheath for the cable rather than a corrugated outer conductor, such as disclosed
in U.S. Pat. No. 3,002,047. Furthermore, this concept of a corrugated outer sheath
has been utilized for standard electrical cables, as opposed to coaxial cables, where
such cables are exposed to considerable flexure, such as disclosed in U.S. Pat. Nos.
2,348,641 and 2,995,616.
[0004] In order to ensure electrical stability for a coaxial cable, the relative location
between the various portions of the outer conductor, the dielectric and the inner
conductor must remain constant during flexure of the cable or the electrical characteristics
may vary. Prior art attempts to ensure this stability have involved the locking of
a corrugated outer conductor to the dielectric surrounding the inner conductor, such
as diclosed in U.S. Pat. No 3,173,990 wherein such inner conductor is a foam polyethylene.
However, such prior art flexible coaxial cables do not have sufficient flexibility
nor do they have sufficient temperature stability, which also affects the electrical
characteristics. These prior art coaxial cables utilize either a tube which is crimped
to provide a corrugated tube or form the outer conductor by means of helically winding
a piece of conductive material, welding the adjacent pieces together to then form
a tube and, thereafter, crimping alternate longitudinal portions so as to provide
a corrugated tube. In both instances, the maximum pitch for the convolutions of the
outer conductor is severly limited. In the first instance, this limitation is primarily
due to rupture of the conductive tube if the crimps are too closely spaced together
whereas, in the second instance, the limitations are primarily due to the inability
to sufficiently control the thickness of the resultant tube which is formed as a thin
enough material cannot be utilized to produce a high pitch. Since the higher the pitch
of the convoluted outer conductor, the greater the flexiblity of the coaxial cable,
these prior art flexible coaxial cables have not been satisfactory where large degrees
of flexure are required together with electrical and temperature stability over a
wide range of flexure.
[0005] Furthermore, these prior art flexible coaxial cable have primarily been of the foam
polythylene or solid dielectric type whereas flexible coaxial cables utilizing spline
dielectrics have not exhibited satisfactory electrical and temperature stability characteristics.
[0006] These disadvantages of the prior art have been overcome to an extent by the prior
invention of U.S. Pat. No 3,797,104 employing a solid dielectric. However, the ability
to provide flexible coaxial cables for certain applications in which a particular
velocity of propagation or lower attenuation was required was somewhat limited as
was the ability to readily change the velocity of propagation of the flexible coaxial
cable to the desired value during manufacture. Moreover, although there have been
prior art attempts to use helically wound dielectrics for coaxial cable, such as disclosed
in U.S. Patent No. 4,346,253; French Patent No. 752,006 and British Patent No. 616,303,
they have not been satisfactorily employed for flexible coaxial cables, particularly
since any change in pitch of the helically wound dielectric during flexing of the
cable wound undesirably change the properties of the cable. These disadvantages of
the prior have been overcome to some extent by the prior invention of U.S. Patent
No. 4,758,685 employing a heat shrinkable dielectric tubing surrounding a helically
wound dielectric beading. However, the process of manufacturing such a flexible coaxial
cable is difficult and necessarily can lend itself to instabilities, such as if the
shrinking were non-uniform thereby resulting in a non-uniform dielectric core which
could cause problems in inserting the core into the outer conductor, and resultant
electrical instability due to the locking of a non-uniform core. These disadvantages
of the prior art are overcome by the present invention which provides an easily controllable
manufacturing process, which yields a highly stable flexible coaxial cable in which
the characteristics of the cable can readily be controlled during the manufacturing
process.
DISCLOSURE OF THE INVENTION
[0007] An improved method for making a flexible coaxial cable having an inner conductor
to which a dielectric material is secured to form a dielectric core for the coaxial
cable, and a flexible outer conductor, such as a convoluted outer conductor formed
from a strip helically wound conductor, employs a solid dielectric starting material,
such as a spline dielectric, or a cylindrical dieletric, or an expanded dielectrics
which is controllably cut, such as by saw blades, using a desired cutting angle and
blade width, in order to cut away a predetermined amount of the solid dielectric starting
material to provide a shaped dielectric core, such as a spiral or helix, from the
solid dielectric starting material. The resulting shaped core, such as single or double
helix, has a resultant predetermined pitch which provides a desired predetermined
velocity of propagation and impedance for the coaxial cable. The resulting helically
shaped core is inserted into the convoluted outer conductor to produce a fast cable
without any locking of the core to the outer conductor. However, to provide additional
stability to the flexible coaxial cable, the core may be locked to the outer conductor
by any of numerous locking methods, such as by way of example, the mechanical crimping
method of the type described in prior U.S. Patent Nos. 3,797,104 and 4,758,685, or
the threadable locking method of the type described in the aforementioned contemporaenously
filed copending U.S. Patent application entitled "Method of Making Flexible Coaxial
Cable Having Threaded Dielectric Core." By calculating in advance the type of cut
to be made to the solid dielectric starting material and the amount of dielectric
material to be removed, various parameters such as impedance, velocity of propagation
or phase length, attenuation, and VSWR, associated with the resulting flexible coaxial
cable, may be readily controlled using the improved method of the present invention.
BRIEF DESCRIPTION OF THE DRAWINGS
[0008]
FIG. 1 is a diagramatic illustration of the presently preferred dielectric cutting
step in accordance with the presently preferred improved method of the present invention
in which a typical solid cylindrical dielectric starting material is being cut to
form a spiral or helix dielectric core;
FIG. 2 is a diagrammatic illustration of a single helix dielectric core provided by
the cutting step illustrated in FIG. 1 in accordance with the presently preferred
improved method of the present invention;
FIG. 3 is a diagrammatic illustration of a double helix dielectric core provided by
the cutting step illustrated in FIG. 1 in accordance with the presently preferred
improved method of the present invention;
FIG. 4 is a diagrammatic illustration of the insertion step for inserting the cut
dielectric core into the convoluted outer conductor in accordance with the presently
preferred improved method of the present invention;
FIG. 5 is a diagrammatic illustration of a typical mechanical crimping step, such
as disclosed in U.S. Patent No. 3,797,104, for mechanically locking the inserted cut
dielectric core to the convoluted outer conductor in accordance with the improved
method of the present invention;
FIG.6 is a cross-sectional view of a preferred embodiment of a flexible coaxial cable
produced by the improved method of the present invention in which the mechanical locking
step of FIG. 5 has been employed;
FIGS. 7 and 8 are diagrammatic illustrations of a typical threadable locking step,
such as disclosed in the commonly owned contemporaneously filed copending U.S. Patent
application entitled "Method of Making Flexible Coaxial Cable Having Threaded Dieletric
Core," for threadably locking the inserted dielectric core to the convoluted outer
conductor in accordance with the improved method of the present invention;
FIG. 9 is a cross sectional view of a preferred embodiment of a flexible coaxial cable
produced by the improved method of the present invention, in which the threadable
locking step of FIGS. 7 and 8 has been employed and the pitch of the cut dielectric
core is the same as the pitch of the convoluted outer conductor;
FIG. 10 is a cross sectional view of a preferred embodiment of a flexible coaxial
cable produced by the improved method of the present invention, in which the threadable
locking step of FIGS. 7 and 8 has been employed and the pitch of the cut dielectric
core is different from the pitch of the convoluted outer conductor;
FIG. 11 is a diagrammatic illustration of a typical spline dilectric which has been
cut in accordance with the improved method of the present invention to form a helix
dielectric core;
FIG. 12 is a diagrammatic illustration of the step of temperature cycling the flexible
coaxial cable between at least a pair of predetermined temperature extremes in accordance
with the improved method of the present invention;
FIG. 13 is a graphical illustration of an impedance trace for a typical flexible coaxial
cable produced in accordance with the improved method of the present invention in
which a solid dielectric has been controllably cut to form a spiral or helix dielectric
core which has been locked to the convoluted outer conductor;
FIG. 14 is a graphical illustration, similar to FIG. 13, of an impedance trace for
a typical flexible coaxial cable in which the solid dielectric core has not been cut
and has not been locked to the convoluted outer conductor;
FIG. 15 is a graphical illustration, similar to FIGS. 13 and 14, which superimposes
the graphs of FIGS. 13 and 14 to illustrate the changes in impedance and velocity
of propagation which occur in the cable of FIG. 14 when the improved method of the
present invention is employed to produce the cable of FIG. 13;
FIG. 16 is a graphical illustration, similar to FIG. 14, of an impedance trace for
a different typical flexible coaxial cable in which the solid dielectric core has
not been cut;
FIG. 17 is a graphical illustration of the VSWR curve for the cable of FIG. 16.
FIG. 18 is a graphical illustration of the attentuation curve for the cable of FIG.
16;
FIG. 19 is a graphical illustration, similar to FIG. 13, of an impedance trace for
a different typical flexible coaxial cable produced in accordance with the improved
method to the present invention in which the solid dielectric has been controllably
cut to form a spiral cut dielectric core;
FIG. 20 is a graphical illustration of the VSWR curve for the cable of FIG. 19; and
FIG. 21 is a graphical illustration of the attenuation curve for the cable of FIG.
19.
BEST MODE FOR CARRYING OUT THE INVENTION
[0009] Referrring now to the drawings in detail, and initially to FIGS. 1-12, the presently
preferred improved method of the present invention shall be described. As discussed
in commonly owned U.S. Patent No. 4,758,685, a spiral or helix type dielectric core
for a flexible coaxial cable enables the velocity of propagation, by way of example,
to be readily controlled during manufacture in accordance with the pitch of the helix,
which also affects the impedance of the dielectric core. However, the method employed
in U.S. Patent No. 4,758,685, for providing this dielectric core involves the use
of a heat shrinkable dieletric tubing over a helically wound dielectric beading which
can result in a non-uniform dielectric core. As shown and preferred in FIGS. 1 and
2, by way of example, the spiral or helix dielectric core 30 in the present invention,
is preferably formed from a solid dielectric starting material 32 which is preferably
cut by adjustable saw blades 34 at a predetermined cutting angle ϑ, using saw baldes
34 of a predetermined cutting width α which effectively determines the web width β
for the resultant spiral dilectric core 30. The dielectric starting material 30 is
preferably initally provided with a conventional inner conductor 36 which comprises
the center conductor 36 for the resultant flexible coaxial cable 38. The dielectric
starting material 30 is preferably secured to the inner conductor 36, such as by bonding
during the extrusion process, so that it is locked to the inner conductor 36.
[0010] As shown by way of example in FIGS. 1 and 2, the solid dielectric starting material
is cylindrical in shape although it can be any desired shape such as, for example,
triangular, and may even comprise a spline 40, such as shown in FIG. 11, which is
then cut to provide the spiral or helix dielectric core 30 which is comprised of the
spiral web 42 of web width β, by way of example, of a predetermined pitch determined
by the cutting angle ϑ and cutting width α. These parameters determine the amount
of dielectric material which is cut away or removed from the solid dielectric 32 which
effectively changes the impedance Z and the velocity of propagation V, as well as
the VSWR and attentuation, such as shown in FIGS. 13-21 to be described in greater
detail hereinafter.
[0011] For example, with respect to the single helix dielectric core 30a illustrated in
FIG. 2, for a dielectric starting material 32 having an initial outer diameter of
0.126 inches, and a starting impedance of 42.1 ohms, the resultant impedance of the
spiral dielectric core 30a is controllably changed to 50.9 ohms by employing the method
of the present invention by utilizing a cutting width α of 0.128 inches for the saw
blades 34, adjusted at a cutting angle ϑ of 36°10', to provide a web width β of 0.50
inches, with a pitch of 0.214 inches and a pitch diameter of 0.095 inches. It should
be noted that the shape of the cut produced by saw blades 34 affects the frequency
range and whether or not moding occurs which would result in high VSWR peaks or spikes
at certain high frequencies, with the effect on VSWR being illustrated by way of example
in FIGS. 17 and 20 which shows a lower VSWR after the controlled spiral cut (FIG.
20) than before (FIG. 17).
[0012] Of course, if it is desired to extend the frequency range of the resultant flexible
coaxial cable 38 and decrease the possibility of moding at higher frequencies, a double
shaped spiral or helix 30b, such as illustrated in FIG.3, can be employed in place
of the single spiral 30a of FIG. 2 for the spiral cut dielectric core 30. In this
instance, the method of the present invention is still basically the same with the
saw blades 34 instead being adjusted to cut a double helix 30b from the solid dielectric
starting material 32. In the example shown in FIG.3, using the same diemeter dielectric
starting material 32 as in FIG. 2, and a starting impedance of 44.1 ohms, the resultant
impedance of the double helix spiral dielectric core 30b is controllably changed to
51.5 ohms by employing the method of the present invention by utilizing a cutting
width α' of 0.075 inches for the saw blades 34, adjusted at a cutting angle ϑ' of
45°30', to provide a web width β' of 0.046 inches, with a pitch of 0.297 inches and
a pitch diameter of 0.108 inches.
[0013] In both instances, in carrying out the preferred method of the present invention,
the saw blades 34 are preferably circular jewelers saw blades which may be used to
cut a solid dielectric starting material of Teflon, TFE, FEP or polyolefin, by way
of example, and are conventionally motor driven by a motor 40, such as at a rate of
approximately 3600 rpm, while the solid dielectric starting material 32 is rotated
and driven or pushed or pulled past the rotating saw blades 34 in the direction of
arrow 42 through holder 44 to provide the spiral cut dielectric core 30. As shown
and preferred, the cutting angle α may readily be adjusted by adjusting the angle
γ of the saw blades 34 with respect to the holder 44 longitudinal axis 46 along which
the dielectric starting material 32 is pulled or driven as it is rotated past the
saw blades 34.
[0014] Of course, if desired, although a spiral dielectric core 30 is shown and presently
preferred, other variations of shapes and styles may be produced using the method
of the present invention which will transmit RF energy efficiently while increasing
the velocity of propagation and adjusting the impedance. This may be accomplished
by changing the amount of blades 34 and their respective widths and the space there
between.
[0015] In any event, in determining the quantity of dieletric material to be cut away from
the solid dielectric starting material 32, the desired impedance Z and the desired
velocity of propagation V are determined by utilizing the following formulas:
where Z= impedance, Ke= dielectric constant, b= electrical diameter of the outer conductor
48, and a= electrical outer diameter of the center conductor 36; and
where v= velocity of propagation, and Ke= dielectric constant.
[0016] As shown and preferred in FIGS. 4 and 6, the spiral cut dielectric core 30, containing
the inner conductor 36, is preferably inserted into a flexible outer conductor, such
as a convoluted outer conductor 50, such as one preferably composed of a corrugated
main conductive member 52 which has been corrugated to produce peaks 54 and valleys
56 in the conductive member 50 at a predetermined pitch, such as the outer conductive
member described in the commonly owned U.S. Patent Nos. 3,797,104 and 4.758,685,or
a corrugated type conductor in which the flexible outer conductor is manufactured
from a seamless or seamed tube. As with that outer conductive member, a helically
wound conductive strip 58 preferably composed of the same conductive material as the
main conductive member 52, is preferably helically wound about the main conductive
member 52 so as to have the strip wound conductor 58 be helically wound about the
peaks 54 of the corrugated main conductive member 52. The conductive strip 58 is preferably
secured to these peaks 54, such as by soldering, so as to form a single unitary composite
conductive member, such as disclosed in U.S Patent Nos. 3,797,104 and 4,758,685, wherein
the peaks 54 are accentuated by the helically wound strip 58 so as to increase the
flexibility of the outer conductor 50. Although the convolutions in the flexible outer
conductor 50 are shown as helical, they can be angular instead without departing from
the present invention.
[0017] Although additional electrical stability may be provided for the resultant flexible
coaxial cable 38 by locking the convoluted outer conductor 50 to the inserted spiral
cut dielectric core 30, if such additional stability is not needed, such as if a change
of 15 degrees in phase were tolerable, then the outer conductor 50 need not be locked
to the inserted spiral cut dielectric core 30 and the resultant flexible coaxial cable
38 can still be a fast cable without locking. However, if such additional electrial
stabilty is desired, then the convoluted outer conductor 50 is preferably locked to
the spiral cut dielectric core 30 by any desired locking method such as, by way of
example, the mechnical locking method disclosed in commonly owned U.S. Patent Nos.
3,797,104 and 4,758,685 and illustrated in FIGS. 5 and 6, or the threadable locking
method disclosed in the commonly owned contemporaneously filed U.S. Patent application
entitled "Method of Making Flexible Coaxial Cable Having Threaded Dielectric Core,"
and illustrated in FIGS. 7-10. In either event, the locked cable 38 is then preferably
temperature cycled in a conventional temperature chamber 60 over a temperature range
of -60 degrees C to + 150 degrees C for 48 hours, by way of example, to provide temperature
stability for the locked cable 38.
[0018] With respect to the mechanical locking method illustrated in FIGS. 5 and 6, the outer
conductor 50 is preferably mechanically crimped to the inserted spiral cut dielectric
core 30 in the manner described in commonly owned U.S. Patent Nos. 3,797,104 and 4,758,685,
in accordance with the desired characteristic impedance of the resultant cable 38
such as by using a conventional time domain reflectometer 62 and mechanical crimping
means 64, with the crimping points preferably being in the valleys 56 of the outer
conductor 50. Since, as shown, the cut dielectric core 30 is a spiral or helix, depending
on its pitch, the mechanical locking may be enhanced by the webs 42 filling additional
voids in the interior of the outer conductor 50 between adjacent valleys 56, since
the inside diameter of the outer conductor 50 is preferably substantially the same
as the outermost outside diameter of the inserted cut dielectric core 30.
[0019] With respect to the threadable locking method illustrated in FIGS. 7-10, if this
method is to be employed then preferably the outermost diameter d₃ of the spiral cut
dielectric core 30 is larger than the inside diameter d₂ of the convoluted outer conductor
50 with the peak-to-peak of the webs 42 preferably being 2/1000-5/1000 larger than
the inside diameter d₂ of the outer conductor 50. The spiral cut dielectric core 30
is then threaded into the outer conductor 50, as shown in FIG. 8, or vice versa, which
locks the core 30 and the outer conductor 50 together as shown in FIGS. 9 and 10,
by way of example, with FIG. 9 illustrating the locking of the core 30 to the outer
conductor 50 when both have the same pitch, and with FIG. 10 illustrating the locking
of the core 30 to the outer conductor 50 when the pitch of the core 30 is different
from the pitch of the outer conductor 50. It should be noted that both of the above
locking methods are applicable whether the electrical starting material 32 was a spline
or a cylindrical dielectric.
[0020] As noted above, by adjusting the cutting saw blades 34 to various angles, depths,
etc., in accordance with the method of the present invention, the user can controllably
change not only the shape and pitch of the spiral, but also the quantity of dielectric
which is removed. As shown in FIGS. 13-21, this enables control over the velocity
of propagation, the impedance, the attenuation, the phase length, and the VSWR of
the resultant cable 38. For example, as shown in FIGS. 13-15, if the velocity of propagation
of a coaxial cable with a solid dielectric is at 73% (FIG. 14) it can readily be controllably
raised to 85% (FIG. 13) with controlled cutting of the dielectric starting material
32, while the resultant impedance is changed from 45.5 ohms to 50 ohms, with FIG.
14 comprising an impedance trace for a coaxial cable having a solid dielectric which
is not locked to the convoluted outer conductor 50, and with FIG. 13 comprising an
impedance trace for a coaxial cable 38, in accordance with the present invention,
in which an inserted spiral cut dielectric core 30 is locked to the convoluted outer
conductor 50. FIG 15 shows the graphs of FIGS. 13 and 14 superimposed on each other.
[0021] FIGS. 16 and 19 comprise additional impedance traces for a different dielectric core
30 in which FIG 16 illustrates the impedance trace for the solid dielectric starting
material 32 before cutting in which the velocity of propagation is at 71% and the
resultant impedance is 45.3 ohms, and FIG. 19 illustrates the impedance trace of the
resultant cable 38 after the solid dielectric starting material 32 has been controllably
cut to produce a spiral cut dielectric core which has a velocity of propagation of
85% and a resultant impedance of 50.1 ohms. In addition, FIG. 17 illustrates a VSWR
before cutting at 1.333 with the frequency of the highest VSWR at 14.82275 GHz, and
FIG. 18 illustrates an attentuation of 58db/100ft. or -2.03db at 18GHz before cutting.
By contrast, FIG. 20 illustrates a desired lower VSWR after cutting of 1.2822 with
the frequency of the highest VSWR being at 15.89675GHz, and FIG. 21 illustrates a
desired lower attentuation of 47db/100ft or -1.64db at 18GHz after cutting.
[0022] Thus, the presently preferred method of the present invention allows various electrical
parameters of the resultant cable 38, such as impedance, velocity of propagation or
phase length, attenuation and VSWR to be determined in advance of manufacture, and
to be readily achieved from a solid dielectric starting material 32 by a controlled
cutting of this material 32 to any desired shape and configuration to provide a spiral
cut dielectric core 30, having an inner conductor 36 which may readily be assembled
with a convoluted outer conductor 50 to provide a fast cable which is a stable flexible
coaxial cable 38 which may be rendered even more stable by locking the core 30 to
the outer conductor 50. Although Teflon is presntly preferred as the dielectric starting
material, other dielectric materials such as polyethylene, TFE or FEP can also readily
be shaped and cut in accordance with the method of the present invention. Moreover,
if desired, portions of the solid dielectric 32, which may be a spline dielectric
or an expanded dielectric, may also be cut out in order to introduce more air into
the cable 38.
[0023] Summarizing the preferred method of the present invention, a solid dielectric starting
material having a bonded center conductor is controllably cut with saw blades to a
desired pitch and shaped by varying the cutting angle and the cutting width, the spiral
cut dielectric core is then inserted into the convoluted outer conductor and, assuming
additional stability is desired, is locked to the outer conductor and the resultant
locked cable is temperature cycled to provide temperature stability for the cable.
[0024] By utilizing the method of the present invention, with the outer conductor remaining
a constant size, after appropriate cutting of the solid dielectric starting material,
the dielectric constant (Ke) can be lowered, the dielectric losses or attenuation
can be lowered, the VSWR can be lowered, the electrical length can be decreased and
the velocity of propagation can be increased. In addition, a larger center conductor
may be employed thereby decreasing conductor losses and attenuation. Thus, these parameters
may be more readily controlled during manufacture to provide a stable flexible coaxial
cable. It should be noted that although the method of the present invention has been
described with respect to manufacturing a flexible coaxial cable, it is also applicable
to the manufacture of rigid or semi-rigid coaxial cable in which the core is to be
shaped or cut as described herein.
1. Method for making a flexible coaxial cable having an inner conductor to which a dielectric
material is secured to form a dielectric core for said coaxial cable and a flexible
outer conductor; comprising the steps of providing a dielectric starting material
comprising a solid dielectric having a predetermined outer diameter; and controllably
cutting said solid dielectric starting material at a desired controllable predetermined
cutting angle and width for cutting away a predetermined amount of said solid dielectric
starting material to provide a desired shaped core from said cut solid dielectric
starting material having a desired predetermined pitch for providing a desired predetermined
velocity of propagation and impedance for said coaxial cable, said cut-shaped solid
dielectric comprising said dielectric core.
2. Method in accordance with claim 1 wherein said cutting step comprises the steps of
cutting away said predetermined amount of said solid dielectric starting material
for providing said desired predetermined impedance, Z, in accordance with the expression
where "Ke" represents the dielectric constant of said dielectric, "b" represents
the electrical diameter of said outer conductor, and "a" represents the electrical
outer diameter of said inner conductor.
3. Method in accordance with claim 1 or 2 wherein said cutting step further comprises
the step of cutting away said predetermined amount of said dielectric starting material
for providing said desired predetermined velocity of propagation, v, in accordance
with the expression
where "Ke" represents the dielectric constant of said material.
4. Method in accordance with claim 1 further comprising the step of inserting said cut-shaped
solid dielectric core into said flexible outer conductor.
5. Method in accordance with claim 1 wherein said solid dielectric starting material
comprises a spline dielectric.
6. Method in accordance with claim 1 wherein said solid dielectric starting material
comprises a cylindrical dielectric.
7. Method in accordance with claim 1 wherein said cutting step comprises the step of
controllably varying said cutting angle for controllably varying the pitch of said
cut-shaped solid dielectric for varying said velocity of propagation and said impedance
for said flexible coaxial cable.
8. Method in accordance with claim 1 wherein said cutting step comprises the step of
cutting said solid dielectric starting material for providing a double helix-shaped
dielectric core from said cut solid dielectric starting material.
9. Method in accordance with claim 1 wherein said cutting step comprises the step of
cutting said solid dielectric starting material for providing a single helix-shaped
dielectric core from said cut solid dielectric starting material.
10. Method in accordance with claim 8 or 9 further comprising the step of locking said
outer conductor to said inserted cut helix-shaped solid dielectric core.
11. Method in accordance with claim 1 wherein said cutting step comprises the step of
controllably varying said cutting width for controllably varying the pitch of said
cut-shaped solid dielectric for varying said velocity of propagation and said impedance
for said flexible coaxial cable.
12. Method in accordance with claim 1 or 4 further comprising the step of temperature
cycling said coaxial cable between at least a pair of predetermined temperature extremes
for a predetermined period of time at each of said extremes, whereby temperature stability
is provided for said flexible coaxial cable.
13. Method in accordance with claim 12 wherein said temperature extremes comprise -60
degrees C to +150 degrees C.
14. Method in accordance with claim 13 wherein said predetermined period of time comprises
48 hours.
15. Method in accordance with claim 1 wherein said solid dielectric starting material
comprises Teflon.
16. Method in accordance with claim 4 or 15 further comprising the step of locking said
outer conductor to said inserted cut-shaped solid dielectric core.
17. Method in accordance with claim 16 wherein said flexible outer conductor comprises
a plurality of helical convolutions, said locking step comprising the step of crimping
said outer conductor to said inserted cut-shaped solid dielectric core between said
helical convolutions of said outer conductor.
18. Method in accordance with claim 16 wherein said locking step comprises the step of
threadably inserting said cut-shaped solid dielectric core into said convoluted outer
conductor until said inserted dielectric and said outer conductor are substantially
coextensive for threadably locking said threadably inserted dielectric core to said
outer conductor for providing a locked flexible coaxial cable due to said threadable
insertion.
19. Method in accordance with claim 1 wherein said cutting step comprises the step of
spirally cutting said solid dielectric starting material for providing said desired
shaped dielectric core from said cut solid dielectric starting material.
20. Method in accordance with claim 19 further comprising the step of locking said outer
conductor to said inserted cut-shaped solid dielectric core.
21. Flexible coaxial cable having an inner conductor to which a dielectric material is
secured to form a dielectric core for said coaxial cable and a flexible outer conductor;
said dielectric core being formed by providing a dielectric starting material comprising
a solid dielectric having a predetermined outer diameter; and said solid dielectric
starting material being controllably cut at a desired controllable predetermined cutting
angle and width for cutting away a predetermined amount of said solid dielectric starting
material to provide a desired shaped core from said cut solid dielectric starting
material having a desired predetermined pitch for providing a desired predetermined
velocity of propagation and impedance for said coaxial cable, said cut shaped solid
dielectric comprising said dielectric core.
22. Flexible coaxial cable in accordance with claim 21 wherein said dielectric core is
further formed by cutting away said predetermined amount of said solid dielectric
starting material for providing said desired predetermined impedance, Z, in accordance
with the expression
where "Ke" represents the dielectric constant of said dielectric, "b" represents
the electrical diameter of said outer conductor, and "a" represents the electrical
outer diameter of said inner conductor.
23. An improved flexible coaxial cable in accordance with claim 21 or 22 wherein said
dielectric core is further formed by cutting away said predetermined amount of said
dielectric starting material for providing said desired predetermined velocity of
propagation, v, in accordance with the expression
where "Ke" represents the dielectric constant of said material.
24. An improved flexible coaxial cable in accordance with claim 21 wherein said dielectric
core is inserted in said flexible outer conductor and locked thereto.
25. An improved flexible coaxial cable in accordance with claim 21 wherein said dielectric
core is formed from a spline solid dielectric starting material.
26. An improved flexible coaxial cable in accordance with claim 21 wherein said dielectric
core is formed from a cylindrical solid dielectric starting material.
27. An improved flexible coaxial cable in accordance with claim 21 wherein said shaped
core comprises a single helix-shaped dielectric core.
28. An improved flexible coaxial cable in accordance with claim 21 wherein said shaped
core comprises a double helix-shaped dielectric core.
29. An improved flexible coaxial cable in accordance with claim 21 wherein said shaped
core is formed by spirally cutting said solid dielectric starting material.
30. An improved flexible coaxial cable in accordance with claim 21 wherein said shaped
core is formed by spirally cutting an expanded solid dielectric starting material.