US3544928A - Mode attenuating support bead for a coaxial transmission line - Google Patents

Mode attenuating support bead for a coaxial transmission line Download PDF

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Publication number
US3544928A
US3544928A US713444A US3544928DA US3544928A US 3544928 A US3544928 A US 3544928A US 713444 A US713444 A US 713444A US 3544928D A US3544928D A US 3544928DA US 3544928 A US3544928 A US 3544928A
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Prior art keywords
transmission line
coaxial transmission
support bead
mode
annular
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US713444A
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Richard C Keiter
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HP Inc
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Hewlett Packard Co
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    • 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
    • H01B11/1834—Construction of the insulation between the conductors

Definitions

  • This invention relates to coaxial transmission lines and, more particularly, to support beads for use therewith.
  • the center con ductor In air-filled coaxial transmission lines the center con ductor is typically supported within the outer conductor by annular dielectric support beads. These dielectric support beads lower the frequency at which the coaxial transmission line supports undesirable circumferential waveguide modes. Moreover, they resonate in the presence of the circumferential waveguide modes. This causes insertion loss and may also cause undesirable coupling between normally isolated parts of the coaxial transmission line. In any case, circuferential waveguide modes in the dielectric support beads may seriously degrade the useful frequency range of the coaxial transmission line.
  • This object is accomplished according to the illustrated embodiments of this invention by providing a coaxial transmission line with a dielectric support bead having an annular resistive film in a region where a circumferential waveguide mode has a finite electric field.
  • FIG. 1 is a sectional perspective view of a coaxial transmission line according to one embodiment of this invention.
  • FIG. 2 is a sectional side view of a coaxial transmission line according to another embodiment of this invention.
  • FIG. 1 there is shown an air-filled coaxial transmission line including a center conductor 10 coaxially supported within and spaced from an outer conductor 12 by an annular dielectric support bead 14.
  • the outer diameter of center conductor 10 is stepped down and the inner diameter of outer conductor 12 is stepped up at dielectric support bead 14, as best illustrated in the sectional view of FIG. 2, to maintain a constant characteristic impedance along the transmission line.
  • An annular channel 16 is formed in one or both sides of dielectric support bead 14 between conductors 10 and 12 to inductively compensate for the change in capac itance caused by these steps in conductors 10 and 12.
  • Circumferential waveguide modes in dielectric support bead 14 are attenuated by an annular resistive film 18 formed in channel 16 at a position where the circumferential waveguide modes have a finite electric field. Resistive film 18 thereby presents a loss to the circumferential waveguide mode causing at least some of its energy to be spent as heat.
  • an annular resistive film 18 is shown, any resistive film positioned on at least one side of dielectric support bead 14 in a region where a circumferential waveguide mode has a finite electric field helps to attenuate that circumferential waveguide mode.
  • a fifty to four hundred ohm per square resistive film, as measured on glass, may be used.
  • the film should be made as small as possible and positioned to present the most loss to the waveguide mode with the smallest possible loss to the normal TEM mode of the coaxial transmission line.
  • the resistive film should not contact conductor 10 and 12.
  • FIG. 2 there is shown another airfilled coaxial transmission line in which support head 14 comprises two concentric annular sections 18 and 20.
  • A11 annular resistive film 22 is formed on the inner periphery of support bead section 18 and/ or on the outer periphery of support bead section 20 in a region where a circumferential waveguide mode to be attenuated has a finite electric field.
  • This structure maximizes the loss presented to the circumferential waveguide mode while at the same time minimizing the loss presented to the normal TEM mode of the coaxial transmission line.
  • the resistive film of this structure does not appreciably alter the reflection coeflicient of dielectric support bead 14.
  • Coaxial transmission line apparatus comprising:
  • annular resistive layer electrically insulated from said conductors and supported on one side of said dielectric element in a region where a circumferential waveguide mode in said dielectric element has a finite electric field to attenuate said circuferential waveguide mode.
  • Coaxial transmission line apparatus comprising:
  • dielectric element coaxially supporting said inner conductor within said outer conductor, said dielectric element comprising a pair of concentric sections;
  • annular resistive layer supported on a peripheral portion of one of said concentric sections along an annular interface therebetween in a region where a circumferential waveguide mode in said dielectric element has a finite electric field to attenuate said circumferential waveguide mode, said resistive layer being electrically insulated from said conductors.

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Description

Dec. 1, 1970 c, n- 3,544,928
MODE ATTENUATIXG SUPPORT BEAU FOR. A COAXIAL 'IRANSMISSION LINE Filed March 15, 1968 RESISTIVE FILM FOR ATTENUATING CIRCUM- FERENTIAL WAVEGUIDE MODE-l8 9iure 1 Fiure 2 INVENTOR RICHARD C. KEITER ATTORNEY United States Patent US. Cl. 333-97 2 Claims ABSTRACT OF THE DISCLOSURE A center conductor is coaxially supported within an outer conductor by a dielectric support bead having an annular resistive film to attenuate circumferential waveguide modes.
BACKGROUND AND SUMMARY OF THE INVENTION This invention relates to coaxial transmission lines and, more particularly, to support beads for use therewith.
In air-filled coaxial transmission lines the center con ductor is typically supported within the outer conductor by annular dielectric support beads. These dielectric support beads lower the frequency at which the coaxial transmission line supports undesirable circumferential waveguide modes. Moreover, they resonate in the presence of the circumferential waveguide modes. This causes insertion loss and may also cause undesirable coupling between normally isolated parts of the coaxial transmission line. In any case, circuferential waveguide modes in the dielectric support beads may seriously degrade the useful frequency range of the coaxial transmission line.
Accordingly, it is the principal object of this invention to attenuate circumferential waveguide modes in the dielectric support beads and thereby extend the useful frequency range of the coaxial transmission line.
This object is accomplished according to the illustrated embodiments of this invention by providing a coaxial transmission line with a dielectric support bead having an annular resistive film in a region where a circumferential waveguide mode has a finite electric field.
Other and incidental objects of this invention will be apparent from a reading of this specification and an inspection of the accompanying drawing in which:
FIG. 1 is a sectional perspective view of a coaxial transmission line according to one embodiment of this invention; and
FIG. 2 is a sectional side view of a coaxial transmission line according to another embodiment of this invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to FIG. 1, there is shown an air-filled coaxial transmission line including a center conductor 10 coaxially supported within and spaced from an outer conductor 12 by an annular dielectric support bead 14. The outer diameter of center conductor 10 is stepped down and the inner diameter of outer conductor 12 is stepped up at dielectric support bead 14, as best illustrated in the sectional view of FIG. 2, to maintain a constant characteristic impedance along the transmission line. An annular channel 16 is formed in one or both sides of dielectric support bead 14 between conductors 10 and 12 to inductively compensate for the change in capac itance caused by these steps in conductors 10 and 12. Circumferential waveguide modes in dielectric support bead 14 are attenuated by an annular resistive film 18 formed in channel 16 at a position where the circumferential waveguide modes have a finite electric field. Resistive film 18 thereby presents a loss to the circumferential waveguide mode causing at least some of its energy to be spent as heat. Although an annular resistive film 18 is shown, any resistive film positioned on at least one side of dielectric support bead 14 in a region where a circumferential waveguide mode has a finite electric field helps to attenuate that circumferential waveguide mode. A fifty to four hundred ohm per square resistive film, as measured on glass, may be used. The film should be made as small as possible and positioned to present the most loss to the waveguide mode with the smallest possible loss to the normal TEM mode of the coaxial transmission line. The resistive film should not contact conductor 10 and 12.
Referring now to FIG. 2, there is shown another airfilled coaxial transmission line in which support head 14 comprises two concentric annular sections 18 and 20. A11 annular resistive film 22 is formed on the inner periphery of support bead section 18 and/ or on the outer periphery of support bead section 20 in a region where a circumferential waveguide mode to be attenuated has a finite electric field. This structure maximizes the loss presented to the circumferential waveguide mode while at the same time minimizing the loss presented to the normal TEM mode of the coaxial transmission line. In addition, the resistive film of this structure does not appreciably alter the reflection coeflicient of dielectric support bead 14.
What is claimed is:
1. Coaxial transmission line apparatus comprising:
an outer conductor;
an inner conductor;
a dielectric element coaxially supporting said inner conductor within said outer conductor; and
an annular resistive layer electrically insulated from said conductors and supported on one side of said dielectric element in a region where a circumferential waveguide mode in said dielectric element has a finite electric field to attenuate said circuferential waveguide mode.
2. Coaxial transmission line apparatus comprising:
an outer conductor;
an inner conductor;
a dielectric element coaxially supporting said inner conductor within said outer conductor, said dielectric element comprising a pair of concentric sections; and
an annular resistive layer supported on a peripheral portion of one of said concentric sections along an annular interface therebetween in a region where a circumferential waveguide mode in said dielectric element has a finite electric field to attenuate said circumferential waveguide mode, said resistive layer being electrically insulated from said conductors.
References Cited UNITED STATES PATENTS 2,434,560 l/1948 Gunter 338-216X 2,946,966 7/1960 Crowe 3338l(A)X 3,008,102 11/1961 St. Clair 333-98(M)X OTHER REFERENCES T. Moreno, Microwave Transmission Design Data, Dover Pub., N.Y., 1948, p. 69 relied on.
PAUL L. GENSLER, Primary Examiner US. Cl. X.R. 333-98
US713444A 1968-03-15 1968-03-15 Mode attenuating support bead for a coaxial transmission line Expired - Lifetime US3544928A (en)

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Cited By (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US6816039B1 (en) * 2003-07-10 2004-11-09 Agilent Technologies, Inc. Coaxial split-bead glass-to-metal seal for high frequency transmission line
US20170047632A1 (en) * 2015-08-11 2017-02-16 Keysight Technologies, Inc. Coaxial transmission line including electrically thin resistive layer and associated methods
US20170047633A1 (en) * 2015-08-11 2017-02-16 Keysight Technologies, Inc. Signal transmission line and electrical connector including electrically thin resistive layer and associated methods
US10418761B2 (en) * 2017-10-09 2019-09-17 Keysight Technologies, Inc. Hybrid coaxial cable fabrication
US11228078B2 (en) * 2017-11-22 2022-01-18 Keysight Technologies, Inc. Electrical plug connector

Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2434560A (en) * 1943-10-07 1948-01-13 Westinghouse Electric Corp Termination for transmission lines
US2946966A (en) * 1957-12-30 1960-07-26 Bell Telephone Labor Inc Nonreciprocal wave transmission
US3008102A (en) * 1957-01-16 1961-11-07 Varian Associates Cavity resonator methods and apparatus

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2434560A (en) * 1943-10-07 1948-01-13 Westinghouse Electric Corp Termination for transmission lines
US3008102A (en) * 1957-01-16 1961-11-07 Varian Associates Cavity resonator methods and apparatus
US2946966A (en) * 1957-12-30 1960-07-26 Bell Telephone Labor Inc Nonreciprocal wave transmission

Cited By (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US6816039B1 (en) * 2003-07-10 2004-11-09 Agilent Technologies, Inc. Coaxial split-bead glass-to-metal seal for high frequency transmission line
US20170047632A1 (en) * 2015-08-11 2017-02-16 Keysight Technologies, Inc. Coaxial transmission line including electrically thin resistive layer and associated methods
US20170047633A1 (en) * 2015-08-11 2017-02-16 Keysight Technologies, Inc. Signal transmission line and electrical connector including electrically thin resistive layer and associated methods
CN108140456A (en) * 2015-08-11 2018-06-08 是德科技股份有限公司 For coaxial transmission line, electric connector comprising tapered portion and thin resistive layer
US10109904B2 (en) * 2015-08-11 2018-10-23 Keysight Technologies, Inc. Coaxial transmission line including electrically thin resistive layer and associated methods
US10418761B2 (en) * 2017-10-09 2019-09-17 Keysight Technologies, Inc. Hybrid coaxial cable fabrication
US11228078B2 (en) * 2017-11-22 2022-01-18 Keysight Technologies, Inc. Electrical plug connector

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