US2602858A - Wave guide dielectric protection - Google Patents

Description

y 1952 R. v. L. HARTLEY WAVE GUIDE DIELECTRIC PROTECTION Filed A 'ril 6, 1946 INVENTOR R VLHARTLE) ATTORNEY Patented July 8, 1952 WAVE GUIDE DIELECTRIC PROTECTION 1' Ralph V. L. Hartley, Summit, N. J., assignor to Bell Telephone Laboratories, Incorporated, New York, N. Y., a corporation of New York Application April 6, 1946, Serial No. 660,029

(or. 17s 44) 2 Claims. 1

This invention relates to wave transmission and more particularly to the transmission of ultra-high frequency waves by means of hollow conductors such as a dielectric wave guide in the form of a metallic pipe containing a gaseous dielectric or a shielded conductor or coaxial cable with a gaseous dielectric occupying the space between the inner and outer conductors.

An object of the invention is to improve the operation of hollow conductors in the transmission of ultra-high frequency waves.

A more specific object of the invention is to lessen the likelihood of the occurrence of dielectric breakdown within a hollow conductor that is being used in ultra-high frequency transmission.

Another specific object of the invention is to substantially raise the breakdown voltage point of the gaseous dielectric withina hollow conductor being used in ultra-high frequency transmission. v

It has been recognized, heretofore, that, when ultra-high frequency waves are being transmitted over a hollow conductor, such, for example, as a dielectric wave guide in the form of a metallic pipe containing a gaseous dielectric, such as air, there is the possibility of breakdown of the dielectric within the guide. Such breakdown, with resulting sparking within the guide, interferes with efficient transmission and is, of course, highly undesirable. It follows that any feasible expedient for reducing the likelihood of such breakdown would be valuable and it is obvious that the value of such expedient would be much greater if the introduction thereof could be made without interference with the normal operation of the conductor and without any major change in the design of said conductor.

The theories of breakdown and sparking are somewhat complicated and there is not complete agreement on the part of all authorities with respect to some of the points involved. There is no occasion in the present instance for a detailed discussion of any of the theoriesor for expression of an opinion with respect to any of the unresolved questions. It may be of value in furthering understanding of the invention, however, if a few basic points be set forth at this time.

In general, the first step in any breakdown is an electron avalanche. This results when an electron is liberated by cosmic rays or some other agency. The liberated electron moves along and collides with molecules thereby producing a number of new electrons and an equal numberof positive ions; each new electron does this same thing. If this avalanche is to develop into a spark, it must in some way produce more elec trons to sustain the process; that is a continuous supply of electrons must be generated. In the case of direct current transmission, this generation may be accomplished by secondary emission resulting from the collision of positive ions with the cathode. In the case of high frequency alternating current-transmission, with which the present invention is concerned, the electrons may be produced photoelectrically in the body of the gas by radiation, mostly ultra-violet, sent out from the initial avalanche and the succeeding discharge.

In accordance with a feature of the present invention, the gaseous dielectric within a hollow conductor is so modified in make-up that the breakdown voltage point of thedielectric is raised substantially.

A further feature of the present invention resides in means whereby the make-up of the dielectric may be modified at desired time intervals without interfering with the normal operation of the conductor. 1 t

In accordance with a specific embodiment of the invention, a wave guide comprises a hollow metallic pipe, a gaseous dielectric (air) being enclosed within the pipe. Means are provided at spaced intervals along the pipe for supplying a polyatomic gas (alcohol vapor) to the interior of the pipe where it mixes with the air dielectric. As will be discussed in greater detail subsequently, applicant has discovered that the addition of this polyatomic gas to the gaseous dielectric results in raising the breakdown voltage point of the dielectric substantially thereby reducing the likelihood of failure of the wave guide when being used for the transmission of ultra-high frequencies.

The expression polyatomic gas as used herein means that each molecule of the gas referred to comprises a plurality of atoms. The expression alcohol" is intended to mean -ordinary or ethyl alcohol (CzHsOH).

A complete understanding of the arrangements contemplated by the present invention, their operation and the advantageous features thereof may be gained from consideration of the following detailed description drawings in which;

Fig. 1 is a longitudinal section of a circular, metallic, wave guide connecting two translating devices and provided withmeans for adding a polyatomic gas to the gaseous dielectric in acand the annexed cordance with features of the present invention;

Fig. 2 is a longitudinal section of a terminal end of a coaxial cable provided with means for adding a polyatomic gas to the gaseous dielectric enclosed within the outer conductor of the cable;

Fig. 3 is a longitudinal section of a modified form ofthe wave" guide of Fig. 1; and

Fig. 4 is an end sectional view of a further type of transmission element provided with means for adding a polyatomic gas to the gaseous dielectric.

Referring now to the drawings, and firstto Fig. 1, there is shown a circular, metallic wave guide ll connecting translatingfievice I2 and load device l3; translating device lzrnay'be, for example, an ultra-high frequency radio transmitter and load device [3 may be, bywayof example,

an antenna such as a dielectric polyrod, a

parabolic reflector or any similar device. A gaseous dielectric, specifically air in this illustrative example, is enclosed by the wave guide.

Wave guides of this and other types and their operation have been described in detail heretofore in various publications, for example, in such patents as 2,129,711, 2,129,712 and 2,129,714, all issued September 13, 1938, to G. CQSouthworth; 2,147,717, issued February 21, 1939, to S. A. Schelkunoff andinthepapers by' J R. Carson et al. and S. A. Schelkunofi appearing in the April 1936, issueof Bell System Technical Journal.

When a wave guide, such as wave guide I! is used for the transmission of ultra-high frequency waves, there is-the possibility, as pointed out above, of breakdown of the gaseous dielectric within the wave guide. As also set forth above, this breakdown, in the instance of high frequency alternating current transmission with which the present invention is concerned, if it is to reach the damaging sparking magnitude, involves the production of electrons photoelectrically in the of each container communicating with the interior of wave guide It through a gas-tight connection. 'Each' container holds aouantity of alcohol,removable plugs, as plug l1, bein provided in each container to permit the liquid to be poured into the containers. The alcohol vapor, a polyatomic gas, which rises from the alcohol, passes from the respectivecontainersthrough the gas-tight connections to the interior of the'wave guide where it mixes with thegaseous dielectric (air) thereof. Vapor seals, as seals 2| and 22, are provided adjacent to devices [2 and l3respcctively as well as at other suitable points in the wave guide. In some instances, particularly when the wave guide terminates ina power device, there will be a tight seal to the-glass vessel of a vacuum tubean'd no additionalivapor seal will be required. j

Applicant has discovered that this'a'ddition of the alcohol vapor to the air dielectric within the wave guide is effective in substantially'raising the breakdownyoltage point of the dielectric thereby'reducing the chance of the failure of the wave guide during transmission. It was pointed out above that under the conditions prevailing during the useof waveguide II, that is for the transmissionof alternating current at high frequency, theestablishment of a breakdown of the dielectric of a magnitude" to result in sparking 4 would involve continuous generation of electrons photoelectrically in the body of the air dielectric by radiation, mostly ultra-violet. Now it is applicants theory that the addition of the polyatomic gas to the dielectric within the wave guide in accordance with the features of the present invention is effective in raising the breakdown voltage pointof the dielectric because of the photoionization referred to is prevented by absorbtion of the ultra-violet radiation. The energy of the "radiation is used up in decomposing the polyatomic molecules.

The alcohol within containers it, it and it should be replaced periodically in order to maintain the'effectiveness of the arrangement. To

facilitate draining, each of the containers is provided with a'suit'able drainage plug, as plug 23.

Ethyl alcohol is particularly applicable to the arrangement of the present invention as it has the property of being able to absorb ultra-violet radiation and has a relatively high volatility thereby assuring entry of the vapor into the wave guide. Other polyatomic gases having these characteristics may also be used, for example,

v methane or ammonia.

Referring now to Fig.2, the arrangement of the present invention is illustrated as applied to a coaxial cable 4|. Cable 4| may be of the general type described in detailin Patent2,376,725, issued May 22, 1945, to L. W. Richardson, deceased (M. M. Richardson, administratrix) and Mr. M. W. Scheldorf and may comprise an inner tubular conductor 42 and an outer tubular conductor 23, the space between said two conductors being filled with a gaseous dielectric, specifically air. One end terminal of the cable is illustrated and it will be observed that the terminal is or" a gastight type. It will beassumedthat the other end of the cable is similarly terminated.

'occupies such space. Container tl is provided with a refill plug 52' and'a drain plug :33.

The purposeof supplying the polyatomic gas to the interior of cable ll where it mixes with the gaseous dielectric of the cable and the theory advanced for the advantageous eilect'of such-action are the same as those discussed above in reference to wave guide H. Thead dition of the polyatomic gas is effective to substantially raise the breakdown voltage of the air dielectric thereby lessening the danger of such breakdown with the resulting sparking attheouter surface of conductor 42 and the inner surface of c'onductor 33.

It is'contemplated that other method or adding the polyatomic'gas to the-dielectric may be of vapor with thegaseous dielectric at the time of construction of the conductor after which the interior of the conductor is sealed. off. By way of illustration of this method there is shown in Fig.3, wave guide- 56, thestructiu'e of which is similar generallyto'that ofwave guide ii of Fig. 1. In the instance of waveguide 155, however, alcohol vapor in properproportion-was mixed with the air dielectric within the wave guide, at

the time of manufacture, after which the interior of the wave guide was sealed-ofi to the passage of gases. Vapor seals, as seals 5'! and 58, are provided where necessary in the wave guide.

In order that alcohol vapor may be added to the mixture within the wave guide when necessary, gas-tight couplings, such as couplings H, '12 and 73, are provided at proper intervals along the Wave guide. On occasion, a container of alcohol may be positioned on the projecting end of a coupling, the hand-operated cut-off valve provided in each coupling (a valve 14) opened and the alcohol vapor supplied to the interior of the wave guide for addition to the mixture of alcohol vapor and air therein.

Referring now to Fig. 4 there is illustrated a transmission element comprising two conductors 8| and 82 positioned within a sheath 83. The area between and surrounding, conductors 8| and 82 is filled with a gaseous dielectric (air) sheath 83 provides a gas-tight enclosure although it need not be electrically insulating. As indicated, alcohol vapor is supplied from alcohol container 84 to the space with sheath 83 where it mixes with the air dielectric therein. The addition of the alcohol vapor to the dielectric is effective to substantially raise the breakdown voltage of the air dielectric thereby lessening the chance of such breakdown with resulting sparking at the surfaces of conductors BI and 82.

It will be apparent that the general arrangement of the present invention offers the particular advantage that its introduction interferes in no way with the normal operation of the conductor and necessitates no change in the basic structure thereof.

While certain specific embodiments of the invention have been selected for detailed description, the invention is not, of course, limited in its application to such embodiments. For example, while the application of a specific polyatomic gas (alcohol vapor) to a specific gaseous dielectric (air) has been described, it will be understood that the use of other polyatomic gases having the required characteristics referred to and the application of the polyatomic gas utilized to gaseous dielectrics other than air are contemplated. Application of the features of the invention to other types of conductors than those illustrated, for ex- 5 also contemplated. In short the embodiments de- 6 scribed should be taken as illustrative of the invention and not as restrictive thereof.

What is claimed is:

1. In combination, a hollow conductive transmission line for transmitting ultra-high frequency waves inclosing a gaseous dielectric at substantially atmospheric pressure and means for absorbing ultra-violet radiation originating in the dielectric during an incipient discharge without material ionization resulting from such absorption, said means comprising a second gas which is polyatomic having the property of absorbing radiation energy of a frequency in the ultra-violet range and having a relatively high volatility supplied to the interior of said hollow line and mixed with the said gaseous dielectric.

2. In combination, a hollow conductive transmission line for transmitting ultra-high frequency waves inclosing air as a dielectric at substantially atmospheric pressure and means for absorbing ultra-violet radiation originating in the dielectric during an incipient discharge without material ionization resulting from such absorption, said means comprising alcohol vapor having the property of absorbing radiation energy of a frequency in the ultra-violet range and supplied to the interior of said hollow line and mixed with the air therein.

RALPH V. L. HARTLEY.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,528,296 Harris May 3, 1925 1,886,153 Perrotti Nov. 1, 1932 1,991,230 Shanklin Feb. 12, 1935 2,034,032 Green Mar. 17, 1936 2,118,667 Domenach May 24, 1938 2,142,226 White Jan. 3, 1939 2,147,717 Schelkunoff Feb. 21, 1939 2,376,725 Richardson May 22, 1945 2,471,744 Hershberger May 31, 1949 FOREIGN PATENTS Number Country Date 167,618 Switzerland May 16, 1934 116,906 Australia Apr. 27, 1943 553,569 Great Britain May 27, 1943

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