Low loss thermal block RF cable and method for forming RF cable

Details Low loss thermal block RF cable and method for forming RF cable Low loss thermal block RF cable and method for forming RF cable

1999-04-01

2001-03-27

Kincaid, Kristine (Department: 2831)

Electricity: conductors and insulators

Conduits, cables or conductors

Conductive armor or sheath

C174S1020SP

Reexamination Certificate

active

06207901

ABSTRACT:

FIELD OF THE INVENTION
The present invention is directed to the field of electromagnetic wave transmission and, more particularly, to a transmission cable for radio frequency (RF) waves.
BACKGROUND ART
In many RF electronic circuit configurations, there is a need to supercool the electronic circuits for improved performance. For example, a thermally cooled amplifier has a lower noise figure than an amplifier operated at ambient temperature. Emerging cryogenic microwave receiver systems that provide enhanced speed and sensitivity include cryogenic cooled components such as cooled mixers and superconductive components for handling signals. These systems place difficult demands on signal connections. The connections to these systems include one end typically at ambient temperature, and an opposite end at a cryogenic temperature. It is highly advantageous to reduce heat conduction along the RF coaxial signal connections to maintain the receiver components at the cryogenic temperature without placing excessive demands on the receiver system refrigeration unit, which commonly has limited cooling capabilities. Input and output via the connections is difficult because the connections need to present minimal thermal load while simultaneously minimizing transmission loss to the input and output signals. The efficiency and power dissipation in the refrigeration units is determined by the refrigeration power supply. The lower the heat load imposed by RF connections, the lower the temperature the refrigeration unit can cool the amplifier, producing a lower overall amplifier noise figure. Consequently, it is important to reduce the heat leakage along RF connections to the cryogenic system.
The problem of providing an input/output RF connection is fundamentally challenging because all materials having high electrical conductivity also have high thermal conductivity. No existing coaxial RF connection solves this problem.
In addition, connections for such cryogenic systems should have low insertion loss, which is a measure of transmission efficiency. Low insertion loss relates to reduced power loss during transmission.
Thus, there is a need for an improved RF connection that has (i) very low thermal conductivity, and (ii) low insertion loss over a range of frequencies.
SUMMARY OF THE INVENTION
The present invention provides an improved RF cable that has (i) very low thermal conductivity, and (ii) low insertion loss over a wide band of frequencies. The RF cable can transmit RF waves such as microwaves at modest currents between points at widely varying temperatures, such as between ambient and cryogenic temperatures. The RF cable transmits RF waves over a band which encompasses more than an octave in the frequency spectrum. The RF waves are typically microwaves, but can be other RF waves as well.
The RF cable comprises a coaxial inner conductor and a coaxial outer shield surrounding the inner conductor in a concentric configuration. The inner conductor can include a first inner conductor section, a second inner conductor section axially spaced from the first inner conductor section, and a third inner conductor section. The third inner conductor section has a length of about &lgr; and includes opposed end portions each having a length of about n&lgr;/4, where n is typically equal to one. One end portion coextends with the first inner conductor section at a break, and the other end portion coextends with the second inner conductor section at another break. The breaks are quarter-wave series sections. The inner conductor sections form a discontinuous axial thermal flow path along the inner conductor. The inner conductor sections are comprised of a highly electrically conductive material to achieve low electrical losses. A dielectric material can be provided between the end portions of the third inner conductor section and each of the first and second inner conductor sections.
The outer shield can include a first outer shield section, a second outer shield section axially spaced from the first outer shield section, and a third outer shield section. The third outer shield section has a length of preferably about &lgr;/2 and includes opposed end portions each having a length of preferably about &lgr;/4. One end portion coextends with the first outer shield section at a break, and the other end portion coextends with the second outer shield section at another break, thereby forming a discontinuous thermal flow path along the outer shield. The first, second and third outer shield sections are comprised of a highly electrically conductive material. A dielectric material can be provided between the end portions of the third outer shield section and each of the first and second outer shield sections.
The RF cable includes at least one break in each of the inner conductor and the outer shield. The breaks prevent the direct flow of heat along the inner conductor and the outer shield, and enable resonant transmission and good electrical conductance.
The RF cable can include, for example, a single break in each of the inner conductor and the outer shield. In this construction, the coaxial inner conductor comprises a first inner conductor section and a second inner conductor section, coextending over a length of preferably about &lgr;/4. The coaxial outer shield comprises a first outer shield section and a second outer shield section, also coextending over a length of preferably about &lgr;/4.
The RF cable can comprise means for maintaining the inner conductor and the outer shield in a substantially fixed configuration. For example, an electrical connector can be provided at the input and output ends. Dielectric material with low thermal conductance can be used to position the concentric conductance. The interior of the RF cable can be maintained at a low selected pressure to provide very low thermal conductance.
The RF cable can have a spiral configuration. The spiral configuration can be formed by depositing a highly electrically conductive material, typically a metal, onto a substrate having very low thermal conductivity, such as a dielectric material sheet. The substrate is wound in a spiral configuration, typically around a form having very low thermal conductivity, to form the spiral configuration. Breaks in the inner conductor and the outer shield form a discontinuous axial thermal flow path along the RF cable. The spiral configuration includes exposed end regions of the metal that enable direct electrical contact to the RF cable.


REFERENCES:
patent: 3828111 (1974-08-01), Berthet
patent: 3970969 (1976-07-01), Sirel et al.
patent: 4323721 (1982-04-01), Kincaid et al.
patent: 4498046 (1985-02-01), Faris et al.
patent: 4719319 (1988-01-01), Tighe, Jr.
patent: 4739633 (1988-04-01), Faris
patent: 4761517 (1988-08-01), Massit et al.
patent: 4809133 (1989-02-01), Faris et al.
patent: 4845311 (1989-07-01), Schreiber et al.
patent: 5120705 (1992-06-01), Davidson et al.
patent: 5138436 (1992-08-01), Koepf
patent: 5324891 (1994-06-01), Huang et al.
patent: 5391836 (1995-02-01), Bortas et al.
patent: 5423110 (1995-06-01), Gauthier et al.
High-Tc Superconductivity in Satelitte Systems: A Technology Assessment, W Gregorwich, Lockheed Martin Advanced Technology Center, IEEE, Feb 2, 1999.

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