US2924795A - Low-loss transmission line - Google Patents

Low-loss transmission line Download PDF

Info

Publication number
US2924795A
US2924795A US478990A US47899054A US2924795A US 2924795 A US2924795 A US 2924795A US 478990 A US478990 A US 478990A US 47899054 A US47899054 A US 47899054A US 2924795 A US2924795 A US 2924795A
Authority
US
United States
Prior art keywords
cable
conductor
insulating material
transmission line
frequency
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Expired - Lifetime
Application number
US478990A
Other languages
English (en)
Inventor
Harold S Black
Jr Samuel P Morgan
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
AT&T Corp
Original Assignee
Bell Telephone Laboratories Inc
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Priority to BE543199D priority Critical patent/BE543199A/xx
Priority to NL201278D priority patent/NL201278A/xx
Application filed by Bell Telephone Laboratories Inc filed Critical Bell Telephone Laboratories Inc
Priority to US478990A priority patent/US2924795A/en
Priority to FR1136311D priority patent/FR1136311A/fr
Priority to GB37430/55A priority patent/GB771670A/en
Application granted granted Critical
Publication of US2924795A publication Critical patent/US2924795A/en
Anticipated expiration legal-status Critical
Expired - Lifetime legal-status Critical Current

Links

Images

Classifications

    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01P—WAVEGUIDES; RESONATORS, LINES, OR OTHER DEVICES OF THE WAVEGUIDE TYPE
    • H01P3/00—Waveguides; Transmission lines of the waveguide type
    • H01P3/18—Waveguides; Transmission lines of the waveguide type built-up from several layers to increase operating surface, i.e. alternately conductive and dielectric layers
    • D—TEXTILES; PAPER
    • D06—TREATMENT OF TEXTILES OR THE LIKE; LAUNDERING; FLEXIBLE MATERIALS NOT OTHERWISE PROVIDED FOR
    • D06P—DYEING OR PRINTING TEXTILES; DYEING LEATHER, FURS OR SOLID MACROMOLECULAR SUBSTANCES IN ANY FORM
    • D06P1/00—General processes of dyeing or printing textiles, or general processes of dyeing leather, furs, or solid macromolecular substances in any form, classified according to the dyes, pigments, or auxiliary substances employed
    • D06P1/44—General processes of dyeing or printing textiles, or general processes of dyeing leather, furs, or solid macromolecular substances in any form, classified according to the dyes, pigments, or auxiliary substances employed using insoluble pigments or auxiliary substances, e.g. binders
    • D06P1/64—General processes of dyeing or printing textiles, or general processes of dyeing leather, furs, or solid macromolecular substances in any form, classified according to the dyes, pigments, or auxiliary substances employed using insoluble pigments or auxiliary substances, e.g. binders using compositions containing low-molecular-weight organic compounds without sulfate or sulfonate groups
    • D06P1/651—Compounds without nitrogen
    • D06P1/65106—Oxygen-containing compounds
    • D06P1/65131—Compounds containing ether or acetal groups
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01B—CABLES; CONDUCTORS; INSULATORS; SELECTION OF MATERIALS FOR THEIR CONDUCTIVE, INSULATING OR DIELECTRIC PROPERTIES
    • H01B11/00—Communication cables or conductors
    • H01B11/18—Coaxial cables; Analogous cables having more than one inner conductor within a common outer conductor
    • H01B11/20—Cables having a multiplicity of coaxial lines
    • H01B11/203—Cables having a multiplicity of coaxial lines forming a flat arrangement
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01P—WAVEGUIDES; RESONATORS, LINES, OR OTHER DEVICES OF THE WAVEGUIDE TYPE
    • H01P3/00—Waveguides; Transmission lines of the waveguide type

Definitions

  • This invention relates to. conductors of high-frequency v waves, and, more particularly, to conductors of the concentric or coaxial type.
  • An object'y of this invention is to reduce skin effect in transmission lines operating at frequencies up to predetermined high-frequency limits.
  • a more specific object is to provide an efiicient yet inexpensive means of improving the attenuation-bandwidth characteristics of insulation lled coaxial cables.
  • skin effect is well known to the art and will be outlined here only because the present invention is concerned with this problem.
  • a more complete ex.- planation thereof canflzve found beginning at page 196 of Fields and Waves in Modern Radio by S. Ramo and l. R. Whinnery, John Wiley & Sons, Inc., 1946.
  • skin effect is the increase with frequency of the resistance of a conductor caused by the ltendency of alternating currents to crowd more and more toward the surface of the conductor as'their frequency is increased.
  • the surfaces toward whichthese currents tend to crowd are those surfaces nearest the fields producing them.
  • Equation 1 is the density of current flowing in the z direction V rfug where f is frequency, ,u is permeability of the conductor, and g is its conductivity.
  • An example of a semi-infinite planefconductor to which Equation 1 is applicable is a plane conductor of nnitedepth below the surface, infinite width, and infinite length. From Equation 1 it is apparent that at a distance below the surface of the conductor the current iz has decreased to 1/ e of its value at the surface. This distance is called the skin depth of penetration of current into the conductor at a given frequency.
  • the 'first of these is the increaserin power losses in the transmission lines which necessitates signal amplification at frequent intervals along Vthe lines.
  • the second is the nonuniformity of the transmissioncharacteristics of the lines for differing signal frequencies.
  • a very well known way of dealing with the first aspect of the problem is to plate a thin layer of highly conductive metal such as silver upon a poorly conducting member such as a less expensive base metal. In this way ⁇ the power losses may be reduced in the neighborhood of the highest utilized frequency by practicing the procedures described in U.S. Patent 2,052,3l7issued to S. A. Schelkunoff, but at best ICC there is only Vinadequate equalization of these losses at various low frequencies.
  • each individual conductor be at least as thin as the skin depth of penetration of waves in the conductorfmetal at the frequency of the waves, It is also necessary that the velocity of propagation of waves in the region surrounding the 'laminated medium be made substantially the sarne as the velocity within this medium.
  • in the laminated lconductor is appreciably less'than the loss in a solid conductor of the same size and, Vfrom very low frequencies up to frequencies at whichthe skin depth becomes conn parable tothe thickness o f the individual conductors, wave attenuation is almost uniform.
  • the attenuation-bandwidth characteristics of the, laminated medium can be improved, within certain limits, in any required degree.
  • one long distance cable built according to the above Clogston disclosure can theoretically transmit all the signals vnow being transmitted by a very large nurnber of conventional long distance lines.
  • it is not economical to employ such a high-transmission-capacity cable For this reason it would be desirable to have available a transmission line possessing attenuation-bandwidth characteristics substantially superior to those of conventional transmission lines previously known, but yet being only slightly more difficult to manufacture than these lines.
  • the present invention prompted by ⁇ this need, is based upon the discovery that a two-conductor insulated transmission line can be improved substantially by the proper insertion into the electromagnetic field between these conductors of a singie thin conductor together with the right kind of insulating material.
  • a hollow cylindrical conductor having a wall ythicknessiless than the skin depth at a predetermined frequency is suitably placed between and axially aligned with the inner and outer conductors of a coaxial cable.
  • Insulating material having a low dielectric constant is used to separate this thin conductor from the inner conductor and different insulating ⁇ material'having asomewhat higher dielectric constant is used toseparate it from the outer conductor.
  • the exact value of the-dielectric constant of thisl latter material and the thickness loffthe lthin'conductor together with certain other physical Adimensions and relationships in this embodiment are critical in -reducing cable attenuation.
  • Fig. 1 is a sectional view of a preferred embodiment of ythe invention taken along the line 1 ⁇ 1 of Fig. 2;
  • Fig. 2 is a cross-sectional view of a preferred embodif ment of the invention
  • Fig. 3 is a cross-sectional view of another preferred embodiment
  • Fig. 4 is a plot of the attenuation vs. frequency characteristic of the cable of Figs. l and 2 asy compared with a standard coaxial cable;
  • Fig. 5 is a plot of the attenuation'vs. frequency char- 'acteristic of the cable of Fig. 3 as compared with a standard coaxial cable.
  • Shells 1, Z, and 3 are made of suitable conducting material, such as copper, andshell 1 may be advantageously formed by copper plating an iron, steel, or other suitable material core, not shown. In addition, shell 3 may be surrounded by a reasonably high impedance shield,.not shown, without detrimentally affecting the operation or the characteristics of the cable.
  • 2 is spaced from and maintained in coaxial relationship with shell 1 by insulating material 4 having a dielectric constant e1 and shell 3 is spaced from shell 2 by insulating material 5 having a dielectric constant e2.
  • Materials which are suitable for insulator 4 are to some extent determinative of what constitutes a suitable material for insulator 5, as will be explained hereinafter, hence a discussion of these materials is postponed until later.
  • theV insulators are 2 17L(aa/b2) i and l is the permeability of inner insulator 4 in henries per meter, n2 is the permeability of outer insulator 5, e1 is the dielectric constant of the inner insulator 4 in farads per meter, e2l is the dielectric constantA of, the outer insulator 5 and'E.('p) isy thecom'ponentof electric eld in volts per meter parallel to the axisat a distance p therefrom.
  • the impedances of the ith conductor are denoted by Z22, Zi?, and Z233 which are a pair of homogeneous -linear equations in terms of the currents I1 and I3. These equations may be satisfied by values of Il and I3 which are not both zero if and only if the determinant of the coefficients vanishes. Setting the determinant equal Ito zero gives a quadratic equaltion in I2:
  • Equation 18 is a perfectly general relation which must ⁇ be satisfied by the propagation constants of the transmission line modes on any system of three coaxial cylindrical conductors separated by two insulators. It 'has two roots, which may be denoted by 11 and F2. (The roots 41, and F2 which correspond to backward traveling waves also satisfy the equation.)
  • the propagation constants may be separated into real and imaginary parts:
  • One purpose of the present invention is to obtain, with a three-conductor transmission system of predetermined outside diameter, a lower attenuation constant at a specified frequency than may be obtained with a conventional two-conductor coaxial system of the same outside di- Inasmuch as there are two transmission-line modes in the three conductor s ystem, as shown by Equations 18 and 19, it is necessary that that mode which has the smaller attenuation constant be utilized, which, for convenience, may be designated as mode l.
  • the corresponding attenuation constant a1' may be minimized by proper choice of materialsand proportions in the three-conductor cable.
  • a would be evaluated at three or more points and a parabolic approximating curve fitted to the points. Setting the rst partial derivatives of the approximating function equal' to zero, a set of simultaneous linear equations is obtained which, when solved, yield the minimum of the approximating function. lf this minimum lies outside of the region which contains the computed points, the variables are adjusted in the direction of the minimum and a new approximating function is tted. This process is repeated until theminimum of the approximating function lies within the region of computed points, which point is then thev minimum value of a1, and the values of the variables may be, in effect, read off.
  • bandwidth does not refer to a range of frequencies, but to a ratio of'frequencies which defines the improved attenuation characteristics of the cable of the invention relative to an ordinary coaxialacable;v
  • Fig. 3 there is shown a second preferred embodiment of the present invention.
  • elementsV and dimensions in Fig. 3 are designated by the same referencecharatcers as like elements and dimensions in Fig. 2.
  • the cable of Fig. 3 differs 'from that of Fig. 2 in that it has a center conductor of solid wire and an outer conductor made of an electrically thick tube, thus providing both mechanical strength and shielding for the cable. ⁇
  • the foregoing mathematical development is applicable except in -the equations of Zag and Zbb.
  • the surface impedance is given by:
  • e1 could be 2.26 (polyethylene) and e2 could be 2.45 (polystyrene).
  • A would have the value 0.084.
  • the center conductor is to carry D.C. power current or where vthe center conductor is copperplated steel for mechanical strength, it may become necessary to make the center conductor approximately equal in size to the center conductor of a coaxial cable.
  • the inner and outer conductors may have the same outside diameters as a coaxial cable, and
  • a low-loss :transmission line for electromagnetic waves comprising inner and outer members of conducting material, a single thin member of conducting material between said inner and said outer members, said thin member ⁇ being separated from said inner member by first insulating material and being separated from said outer member by second 'insulating material, the characteristic wave propagation velocity of said first insulating material being greater than that of said second insulating material, and the thickness of said thin member is between one-half and one skin depth at the highest frequency of operation of the transmission line.
  • a low-loss transmission line for electromagnetic waves comprising an inner cylindrical member of con'- ducting material, and an outer cylindrical member of conducting material coaxial with said inner member, a single thin member of conducting material between said inner and outer members and coaxial therewith, said thin member being separated from said inner member of lirst insulating material and being separated from said outer member by a second insulating material, the intrinsic wave propagation velocity of said first insulating material being greater than that of said second insulating material, said thin member having a thickness greater than onehalf and less than one skin depth at the highest frequency of waves to be transmitted.
  • a low-loss transmission line for electromagnetic waves as claimed in claim 5 wherein both the dielectric constant and the permeability of the rst insulating material diler from the ycorresponding constants of said second insulating material.
  • a low-loss transmission line for electromagnetic waves according to claim 5 wherein the spacing between said thin member and said inner conducting member is less than the spacing between said thin member and said outer conducting member.
  • a low-loss transmission line for electromagnetic waves comprising an inner hollow cylindrical member of conducting material, an outer cylindrical member of conducting material coaxial with said inner member, a single thin intermediate member of conducting material between said inner and outer members and coaxial therewith, said thin member being separated from said inner member by a first insulating material and being separated from said outer member by a second insulating material,
  • the intrinsic wave propagation velocity ofisaid 'first insulating wave material being .greater than that of said second insulating material, saidthin memberhaving-a thickness greater than one-half 'and less than one skin depth at the highest frequency of waves to be transmitted, said inner member having a thickness greater than one and less than two skin depths thick at said frequency and said outer member having a thickness greater than'oney and less than two skin depths thick at said highest fre ⁇ quency.
  • a low-loss transmissionfline for electromagnetic waves comprising a solid inner member of conducting material, an outer cylindrical member of conducting material coaxial with said inner member, a single thin intermediate member of conducting material between said inner and outer members and coaxial therewith, said thin member being separated from said inner member by a rst insulating material and being separated from said outer member by a second insulating material, the intrinsic wave propagation velocity of said rst insulating material being greater than that of said second insulating material, said thin-member having a thickness greater than one-half and less than one skin depth at the highest frequency of waves to be transmitted, the outside diameter of said intermediate member being greater than one and one-third times the outside diameter of said inner member.
  • a levi/loss transmission line for electromagnetic waves comprising a soldiinner-vmember of conducting material, the surface of said inner member being coated with a conducting material yof greater conductivity than that of the material of said inner member, angouter cylindrical member of conducting material coaxial with said inner member, the inmner surface of said outer member being coated with a conducting material of greater conductivity than that of.
  • said outer member a single thin intermediate member of conducting material between said inner and outer members and coaxial therewith, said thin member being separated from said inner member by a first insulating material and being separated from said outer member by a second insulating material, the intrinsic wave propagation velocity of said rst insulating material being greater than that of said second insulating material, said thin member having a thickness greater than one-half and less than one skin depth at the highest frequency of waves to be transmitted.

Landscapes

  • Engineering & Computer Science (AREA)
  • Textile Engineering (AREA)
  • Communication Cables (AREA)
  • Waveguides (AREA)
US478990A 1954-12-31 1954-12-31 Low-loss transmission line Expired - Lifetime US2924795A (en)

Priority Applications (5)

Application Number Priority Date Filing Date Title
BE543199D BE543199A (enrdf_load_stackoverflow) 1954-12-31
NL201278D NL201278A (enrdf_load_stackoverflow) 1954-12-31
US478990A US2924795A (en) 1954-12-31 1954-12-31 Low-loss transmission line
FR1136311D FR1136311A (fr) 1954-12-31 1955-08-08 Ligne de transmission à faibles pertes
GB37430/55A GB771670A (en) 1954-12-31 1955-12-30 Improvements in or relating to coaxial transmission lines for high frequency electromagnetic waves

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
US478990A US2924795A (en) 1954-12-31 1954-12-31 Low-loss transmission line

Publications (1)

Publication Number Publication Date
US2924795A true US2924795A (en) 1960-02-09

Family

ID=23902212

Family Applications (1)

Application Number Title Priority Date Filing Date
US478990A Expired - Lifetime US2924795A (en) 1954-12-31 1954-12-31 Low-loss transmission line

Country Status (5)

Country Link
US (1) US2924795A (enrdf_load_stackoverflow)
BE (1) BE543199A (enrdf_load_stackoverflow)
FR (1) FR1136311A (enrdf_load_stackoverflow)
GB (1) GB771670A (enrdf_load_stackoverflow)
NL (1) NL201278A (enrdf_load_stackoverflow)

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3865971A (en) * 1972-08-08 1975-02-11 Nippon Telegraph & Telephone Submarine coaxial cables

Families Citing this family (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
FR2176574B1 (enrdf_load_stackoverflow) * 1972-03-24 1974-08-02 Prache Marie Pi Rre

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3865971A (en) * 1972-08-08 1975-02-11 Nippon Telegraph & Telephone Submarine coaxial cables

Also Published As

Publication number Publication date
GB771670A (en) 1957-04-03
FR1136311A (fr) 1957-05-13
NL201278A (enrdf_load_stackoverflow)
BE543199A (enrdf_load_stackoverflow)

Similar Documents

Publication Publication Date Title
US2797394A (en) Electrical conductor having composite central dielectric member
US2769148A (en) Electrical conductors
US3668574A (en) Hybrid mode electric transmission line using accentuated asymmetrical dual surface waves
US2796463A (en) Composite conductors
US2262134A (en) Ultrahigh frequency transmission line termination
US2929034A (en) Magnetic transmission systems
FI76449C (fi) Bandledning.
US2950454A (en) Helix wave guide
US2769149A (en) Spirally wound composite electrical conductor
US2924795A (en) Low-loss transmission line
US2034033A (en) Shielded stranded pair
US2831921A (en) Loaded laminated conductor
US2825760A (en) Magnetically loaded electrical conductors
US2038240A (en) Transmission system
US2034047A (en) Coaxial circuit with stranded inner conductor
US2879318A (en) Shield for electric current apparatus
Liu et al. Study of dielectric loss and conductor loss among microstrip, covered microstrip and inverted microstrip gap waveguide utilizing variational method in millimeter waves
US2769170A (en) Composite antenna structure
US3601720A (en) Helical waveguide with varied wall impedance zones
US2779925A (en) Composite coaxial resonator
US3560889A (en) Termination for ultra-high-frequency and microwave transmission lines
CN214624545U (zh) 一种镀有屏蔽层的数据传输线
GB750692A (en) Improvements in or relating to electrical conductors
US1979402A (en) Concentric shield for cables
US2769150A (en) Laminated conductor