US3199054A

US3199054A - Shielded delay line

Info

Publication number: US3199054A
Application number: US63198A
Authority: US
Inventors: James E Holland; Earl M Polzin
Original assignee: Thompson Ramo Wooldridge Inc
Current assignee: Northrop Grumman Space and Mission Systems Corp
Priority date: 1960-10-17
Filing date: 1960-10-17
Publication date: 1965-08-03
Anticipated expiration: 1982-08-03

Description

INSERTlON Loss m DB INSERTION Loss m DB \NsERnoN Loss IN DB Ln-PQJ Aug. 3, 1965 Filed Oct. 17, 1960 2 Sheets-Sheet 2 REFERENCE Y Mm. \NSERT\ON Loss MAX. lNSERTlON L055 FREQUENCY IN KM C,

REFERENQE FREQUENCY IN KMC REFERENCE] FREQUENCY. IN KMC fAMl-ZS E. HOLLAND 1 7 EARL M. POLZ/N INVENTORS United States Patent 3,199,054 SIHELDED DELAY LINE ames E. Holland, Rolling Hills, and Earl M. Polzin, Palos Verdes Estates, Califi, assignors, by mesne assignments,

to Thompson Rama Wooldridge Inc., Cleveland, Ohio,

a corporation of Qhio Filed Oct. 17, 1960, Ser. No. 63,198 Claims. (Cl. 333-31) This invention relates to electromagnetic energy transmission apparatus and more particularly to energy Wave transmission devices in which interaction of a signal propagated therein between adjacent sections thereof is substantially eliminated and in which the insertion loss over the operating range of frequencies of the device may be substantially equalized Where a wave transmission device which is not completely enclosed by a metallic boundary is placed in a configuration other than an isolated straight line, inlIBl'EICiiOIl of a signal propagated therein with adjacently disposed sections thereof has long been a problem in the art. This interaction can, under many circumstances, cause variations in the insertion loss of the Wave transmission device. Where the wave transmission device is utilized as a delay line, it has been found that variations in the delay experienced by .a signal that is propagated along the delay line will occur as a result of the signal interaction between adjacently spaced sections of the delay line. One attempt which has been made to solve this problem is tha of spacing the adjacent sections of the delay line so that the distance between them is sufiicient to prevent interaction of the signal which is propagated along the line.

This problem of interaction of the signal in adjacent sections of a wave transmission device becomes particularly acute when a transmission line or the like is used as a delay line and is placed in the form of a helix, spiral or the like, to obtain a maximum delay time within a minimum physical space. By using such a geometric configuration, the interaction of the signal between adjacent turns of the wave transmission device is diflicult to control. Heretofore, inteiturn spacing has been used in an attempt to solve the interaction problem. Although excellent results have been obtained in this manner, the resulting delay line is physically larger than is desirable and the weight thereof is increased beyond preferred limits. The relatively large size and weight is undesirable in many applications. Where solid dielectric material having conductors spaced thereon is used as the transmission line, physical strength al o becomes quite an important factor, since, in some cases, the dielectric material which is utilized is hard and brittle.

it is also well known in the prior art that, when using transmission devices such as the solid dielectric type above referred to, the insertion loss of the device varies with the frequency. in many applications it becomes desirable to obtain a relatively constant insertion loss over the frequency band of the particular apparatus irrespective of the signal frequency. For example, in some electronic systems where a signal is to be delayed for a predetermined time before application to a sensing device, it is important that the delayed signal have subtantially the same amplitude irrespective of frequency.

Accordingly, it is an object of the present invention to provide a transmission device in which interaction of the "Ice signal propagated along adjacently positioned sections thereof is substantially eliminated.

It is another object of the present invention to provide a transmission device in which adjacent sections thereof may be spaced closer together than has heretofore been possible in the prior art.

It is another object of the present invention to provide a transmission device which may be used as a signal delay line and in which delay variations as a result of the interaction of electromagnetic fields set up by the signal propagated along the delay line are substantially reduced.

It is another object of the present invention to provide a transmission device which may be used as a delay line and in which the variation in insertion loss is substantially reduced.

It is another object of the present invention to provide a transmission device whichmay be used as a delay line and in which the voltage standing wave ratio thereof is substantially reduced.

It is another object of the present invention to provide a transmission device which may be used as a delay line and which is smaller and more rugged than delay lines heretofore known in the prior art.

It is another object of the present invention to provide a transmission device which has a relatively constant insertion loss over its operational frequency band.

The novel features of the present invention are set forth in the appended claims. Further objects and advantages of the present invention may be ascertained from a reading of the following description taken in conjunction with the accompanying drawings which are presented by way of example only and are not intended as a limitation upon the scope of the present invention and in which:

FIGURE 1 is an illustration of a portion of one type of transmission device which may be utilized in accordance with the present invention;

FIG. 2 is a side-elevational View, partly in cross section, of a transmission device in the form of a delay line in accordance with one embodiment of the present invention;

FIG. 3 is a fragmentary view, partly in cross section, of a transmission device in the form of a delay line in accordance with another embodiment of the present invention;

FIG. 4 is a side-elevational view, partly in cross section, of a transmission device in the form of a delay line in accordance with an alternative embodiment of the present invention;

FIG. 5 is a graph illustrating insertion loss as compared to frequency of a prior art delay line;

FIG. 6 is a graph illustrating insertion loss versus frequency of a delay line in accordance with one embodiment of the present invention; and

FIG. 7 is a graphillustrating insertion loss versus frequency of a delay line in accordance with another embodiment of the present invention.

In accordance with one aspect of the present invention, there is provided a transmission device in the form of a wave guide which includes metallic conductors upon only a portion of the surface of the wave guide. The wave guide is arranged in a configuration such that sections thereof are disposed adjacent other sections thereof. Metallic shielding means is disposed between adjacent sections of the wave guide to shield the adjacent sections from electromagnetic fields set up by the signal propagated along 3 the wave guide while at the same time not interfering with the signal which is propagated along the wave guide.

In accordance with another aspect of the present invention, an electromagnetic energy absorbing material is disposed about an elongated wave transmission device to maintain the insertion loss of the wave transmission device substantially constant over the entire operating freuency range thereof.

In accordance with a specific embodiment of the present invention, there is provided a wave guide comprising an elongated member of high dielectric constant material having metallic conductors spaced on opposed substan tially parallel surfaces thereof. The elongated member is placed substantially in the form of a helix and is disposed within a plastic foam. Portions of the plastic foam are removed from between adjacent turns of the elongated helical member. The space which is thereby provided is filled with a material which provides shielding between adjacent turns and which is capable of absorbing electromagnetic energy. ln this manner there is provided a wave guide which can operate as a delay line and in which the interaction between adjacent turns thereof as a result of an electromagnetic energy wave propagated therealong is substantially eliminated and in which the insertion loss over the operating frequency range of the delay line remains substantially constant.

Referring now to the drawings and more particularly to FIG. 1 thereof, there is illustrated a transmission device such as a section of wave guide which may be utilized in accordance with the present invention. Although the following description of the present invention will be given with reference to a Wave guide which consists of a high dielectric constant material, such as titanium dioxide, having metallic conductors affixed to opposed substantially parallel surfaces thereof and which may extend over the entire area of each of the opposed surfaces thereof, it should be expressly understood that the present invention is applicable to any type of transmission device which is not completely surrounded by a metallic boundary.

As illustrated in FIG. 1, a transmission device which may be utilized in accordance with the present invention includes an elongated member of high dielectric constant material 11 having spaced on opposite surfaces thereof metallic electrically

conductive layers

12 and 13. The dielectric material 11 may be any known high dielectric constant material within which electromagnetic energy waves may be propagated. Examples of such material are T efion, polystyrene, polyethylene, fiber glass, quartz, barium titanate, titanium dioxide or the like. The metallic electrically

conductive layers

12 and 13 which are applied to the opposite surfaces of the dielectric material 11 may be any metallic coating which is desired, but is preferably silver. The layers may be applied by any means known to the prior art so that the layers are relatively thin.

As is known to the prior art, a wave of electromagnetic energy which is propagated within a transmission device such as that illustrated in FIG. 1 extends outside the boundaries thereof to some degree depending upon the dielectric constant of the material as compared to that of its operating atmosphere and the frequency of the energy wave. As the wave of energy is propagated along the transmission device, large electric fields are established at the uncoated boundaries of the high dielectric mate rial as a result of the difference between the dielectric constant of the material and of the atmosphere in which it is operating. However, the electric and magnetic fields extend beyond the boundaries of the dielectric material. The lower the frequency which may be propagated along the particular wave transmission device illustrated in FIG. 1, the greater are the electric and magnetic fields which extend beyond the boundaries of the dielectric material. As the frequency increases, the electric and magnetic fields are bound more and more within the boundaries of the dielectric material and between the metallic coatings disposed thereon. It is therefore apparent that if, in accordance with prior art teachings, a wave transmission device such as illustrated in FiG. l is placed in such a geometric configuration that various sections thereof are disposed adjacent each other, the adjacent sections must be so spaced as to prevent interaction between the electromagnetic fields extending beyond the boundaries thereof for the lowest frequency which is to be generated within and propagated along the particular wave transmission device.

Referring now more particularly to FIG. 2,' there is illustrated an elongated member of'a wave transmission device which has been placed in the geometric configuration of a helix. Such a geometric configuration is particularly adaptable to such uses as a delay line, particularly at microwave frequencies. The helical configuration permits a greater delay per unit of physical length along the longitudinal axis of the helix. it is to be expressly understood, however, that any particular geometric configuration, such as a spiral, a sinuous shape, straight lines, or the like, may be used in accordance with the teachings of the present invention.

As illustrated in FIG. 2, the helical delay line 2?; comprises a plurality of turns formed of an elongated striplike member of the character illustrated in FIG. 1. As described heretofore, the dielectric strip is metallized on both of the large area surfaces. The strip member is edge-wound peripherally of an inner shield 25 so that the metallized right-hand surface of one turn is disposed in facing relation to and spaced from the left-hand surface of the next adjacent turn. That is, in accordance with the presently preferred embodiment, the strip member is edge-wound so that the metallic coated surfaces lie in planes substantially normal to the longitudinal axis of the inner shield cylinder 25. It should be expressly understood that the foregoing edge-wound arrangement is not essential to the present invention. It is contemplated that the strip member might alternatively be fiat-wound so that the metallic coated surfaces would be generally internal and external of the helix without departing from the scope of the invention. The helical delay line 21 of FIG. 2 is disposed within a container such as a metal housing 22. Standard connectors 25) are provided for launching or generating a signal within and removing it from the helical delay line 21. Spaced from and disposed between adjacent turns of the helical delay line 21 are shielding members 23. The shielding members 23 prevent the electromagnetic field which is generated by the signal that is propagated along the helical delay line 21 and which extends beyond the boundaries thereof from interacting with the electromagnetic field which is present in an adjacent turn of the helical delay line. Tie shielding members may be constructed of any metal desired, but preferably are silver or any low-loss material. in this manner, the spacing between adjacent turns of the helical delay line 21 may be greatly reduced from that which has heretofore been known in the prior art. The requirements for a shielding in accordance with the present invention are (1) that the shielding be spaced in such a manner as to prevent interaction of the electromagnetic field which is gen erated within the Wave transmission device, and (2) that the shielding does not interfere with the signal which is propagated along the transmission line. It has been found that, when using a helical delay line as illustrated in FIG. Substantially all interaction of the electromagnetic field propagated along the adjacent turns of the delay line has been eliminated.

The outer surface 24 of the-metal housing 22 may also be used as a portion of the shield as well as an inner member 25 which is inserted within the housing 22 and is substantially concentric with the outer surface 24. In this manner the helical delay line 21 is completely surrounded by a shield. Such a shield not only prevents interaction of the signal in adjacent turns, but also prohibits any signals exterior to the wave guide from interfering with the signal propagated therein.

As can be seen by reference to FIG. 5, in which insertion loss in decibels is plotted along the ordinate and frequency in kilomegacycles is plotted along the abscissa for an unshielded prior art delay line operating over a frequency band of approximately two to four kilornegacycles, the interaction of the signal between adjacent sections of the delay line produces an undesirable interference signal.

The insertion loss versus frequency of a delay line constructed in accordance wifla the present invention as illustrated in FIG. 2 is shown in FIG. 6. It can readily be seen that substantially all of the signal interaction has been eliminated and a smooth response is obtained over the entire operating frequency band.

As above pointed out, as the frequency of a signal which is generated within a delay line, such as illustrated in FIG. 1 or FIG. 2, is increased, the electromagnetic field is maintained more and more within the boundaries of the high dielectric constant material. Since this occurs, the losses which the signal experiences as a result of being propagated along a particular wave transmission device increase as the frequency increases, since the losses imparted to the signal by the high dielectric constant material are greater than that which the signal would experience if it were propagated through air. As a result thereof, the insertion loss of a signal propagated along a delay line, as illustrated in FIG. 2, increases as the frequency increases. It is sometimes desired that a signal which is propagated along a delay line have a constant insertion loss irrespective of the frequency which is generated therein. When such a result is desired for any particular application, a material may be placed between adjacent turns of a helical delay line, of the type illustrated in FIG. 2, which will absorb electromagnetic energy which impinges thereon. In such a manner, the electromagnetic energy extending beyond the transmission device at the lower frequencies is absorbed by the electromagnetic energy absorbing material, hereinafter referred to as lossy material, whereas at the higher frequencies less of the electromagnetic energy extends beyond the transmission line and therefore is not affected by the lossy material disposed between adjacent turns.

The lossy material may be inserted in any manner desired between the turns, and, in accordance with a presently preferred embodiment of the present invention, the lossy material may be afixed directly to the metallic shielding members inserted between adjacent turns of the helix, as illustrated at 26 in FIG. 3. As is illustrated, there is provided a helical delay line having a shielding member 23 disposed between each of the adjacent turns of the helical delay line, and the lossy material 26 is disposed on opposite surfaces of each of the shielding members 23. In this manner, there is provided a helical delay line in accordance with the present invention which provides a constant insertion loss irrespective of the frequency of the signal generated Within the delay line and which eliminates interaction between the electromagnetic fields generated as a result of the signal propagated along the delay line.

The lossy material 26 affixed to the opposite surfaces of the shielding members 23 may be any carbon base compound, such as Aquadag, or may be a metallized plastic material, such as metallized fiber glass. The lossy material is applied in any manner desired so as to obtain very thin coatings on the order of a few thousandths of an inch thick. For example, the material may be sprayed or painted or may be affixed in sheets.

Referring now more particularly to FIG. 4, there is illustrated an alternative embodiment of a helical delay line in accordance with the teachings of the present invention. As is therein illustrated, a container 31 has disposed therein a helical delay line 32 which is constructed of a wave guide similar to that illustrated in FIG. 1. Standard connectors 30 may be used for applying a signal to and removing it from the delay line 31. A plastic foam material 33 is disposed within the container 31 and completely surrounds the helical delay line 32. Portions of the plastic foam 33 are removed from between adjacent turns of the helical delay line 32 to provide recesses 34 therein. A material is then inserted within the open portions of the plastic foam 33, as illustrated at 35. This material operates to perform the functions of both shielding and absorbing the electromagnetic energy which is radiated from the adjacent turns of the helical delay line 32. One example of a material which performs the dual function as above described is a mixture of silver paint and a carbon base material.

A delay line constructed in accordance with the configurations illustrated in either FIG. 3 or FIG. 4 not only provides the electrically desired operation as above described, but as well provides a substantially mechanically stronger apparatus than has heretofore been known in the prior art. For example, the shielding members 23 as illustrated in FIG. 2 provide rigidity to the wave guide device, and the plastic foam provides a shock absorbing material. Therefore, even if the helical delay line were constructed of exceedingly brittle material, the plastic foam would tend to absorb whatever shocks may be imparted to the container having the delay line mounted therein.

Referring 'now more particularly to FIG. 7, there is shown a graph of insertion loss versus frequency when using a delay line similar to that illustrated in FIG. 3.

As can be seen from a comparison of FIGS. 6 and 7, the response of the shielded delay line in accordance with this embodiment of the present invention displays a relatively constant insertion loss over the entire operating frequency band. 7

There has thus been disclosed a wave transmission device in which interaction between adjacent sections of such a device as a result of the electromagnetic energy radiated therefrom is substantially eliminated, and also in which there may be a constant insertion loss over the operating range of frequencies irrespective of variation of such operating frequency.

What is claimed is:

1. A device for receiving and transmitting waves of electromagnetic energy, comprising: an elongated member, formed of a material having a dielectric constant substantially higher than air, and having an electrically conductive layer on opposed surfaces thereof and having a convoluted form such that at least first and second portions of said member are disposed in side-by-Side adjacency; means for launching an electromagnetic energy wave within said elongated member affixed to at least one end thereof; shielding means disposed between said first and second portions; and a material for absorbing electromagnetic energy radiated from said elongated member disposed upon at least a portion of the surface of said shielding means adjacent said elongated member.

2. A device for receiving and delaying waves of electromagnetic energy, comprising: an elongated member, formed of a material having a dielectric constant substantially higher than air, and having an electrically conductive layer on opposed surfaces thereof and having -a substantially helical form; means for launching an electromagnetic energy wave within said helically formed member afiixed to at least one end thereof; .a metallic container for said helically formed member, said container having an outer portion completely surrounding the exterior of said helically formed member, said container'having a central portion disposed internally of said helically formed member; and a substantially planar metallic member having a substantially helical configuration disposed between adjacent turns of said helically formed member and extending between the outer and inner portions of said container whereby each turn of said helically formed member is completely surrounded by a metallic shield.

3. A device for receiving and delaying waves of electromagnetic energy, comprising: an elongated member, formed of a material having a dielectric constant substantially higher than air, and having an electrically conductive layer on opposed surfaces thereof and having a substantially helical form; means for launching an electromagnetic energy wave within said helically formed member aflixed to at least one end thereof; a metallic container for said helically formed member, said container having an outer portion completely surrounding the exterior of said helically formed member, said container having a central portion disposed internally of said helically formed member; a substantially planar metallic member having a substantially helical configuration dis posed between adjacent turns of said helically formed member and extending between the outer and inner portions of said container, whereby each turn of said helically formed member is completely surrounded by a metallic shield; and a material for absorbing electromagnetic energy radiated from said helically formed member disposed upon at least a portion of the surface of said metallic member adjacent said helically formed member.

4. A device for receiving and transmitting waves of electromagnetic energy, comprising: an elongated member, formed of a material having a dielectric constant substantially higher than air, and having an electrically conductive layer on opposed surfaces thereof and having a convoluted form such that at least first and second portions of said member are disposed in side-by-side adjacency; means for launching an electromagnetic energy wave within said elongated member affixed to at least one end thereof; a metallic container disposed about and completely surrounding said elongated member; a shock absorbing material within said container and contacting said elongated member; and shielding means within said container and disposed extending between said portions, said shock absorbing material being disposed between said elongated member and said shielding means.

5. A device for receiving and transmitting waves of electromagnetic energy, comprising: an elongated member, formed of a material having a dielectric constant substantially higher than air, and having an electrically conductive layer on opposed surfaces thereof and having a convoluted form such that at least first and second portions of said member are disposed in side-by-side adacency; means for launching an electromagnetic energy wave within said elongated member affixed to at least one end thereof; a metallic container disposed about and completely surrounding said elongated member; a shock absorbing material within said container and contacting said elongated member; shielding means within said container and extending between said portions, said shock absorbmg material being disposed between said elongated member and said shielding means; and a material for absorbing electromagnetic energy radiated from said elongated member disposed upon at least a portion of the surface of said shielding means adjacent said elongated member.

6. A device for receiving and delaying waves of electromagnetic energy, comprising: an elongated member, formed of a material having a dielectric constant substantially higher than air, and having an electrically conductive layer on opposed surfaces thereof and having a substantially helical form; means for launching an eletromagnetic energy wave with said elongated member afiixed to at least one end thereof; a metallic container disposed about and completely surrounding said elongated member; a shock absorbing material within said container and contacting said elongated member; and shielding means disposed between adjacent turns of said elongated member to thereby substantially prevent interaction of the signal propagated along adjacent turns of said elongated member.

7. A device for receiving and delaying waves of elec- 8 tromagnetic energy, comprising: an elongated member, formed of a material having a dielectric constant substantially higher than air, and having an electrically conductive layer on opposed surfaces thereof and having a substantially helical form; means for launching an eletromagnetic energy wave with said elongated member affixed to at least one end thereof; a metallic container disposed about and completely surrounding said helically formed member, said container having an outer portion and an inner portion each extending longitudinally of said helically formed member and spaced from the outer and inner surfaces thereof respectively; a shock absorbing material surrounding said helically formed member and disposed within the inner and outer portions of said container; and shielding means disposed between adjacent turns of said helically formed member and through said shock absorbing material.

3. A device for receiving and delaying waves of electromagnetic energy, comprising: an elongated member, formed of a material having a dielectric constant substantially higher than air, and having an electrically conductive layer on opposed surfaces thereof and having a substantially helical form; means for launching an electromagnetic energy wave within said member affixed to at least one end thereof; a metallic container disposed about and completely surrounding said member, said container having an outer portion and an inner portion each extending longitudinally of said member and spaced from the outer and inner surfaces thereof respectively; a shock absorbing material surrounding said member and disposed within the inner and outer portions of said container; and shielding means disposed between adjacent turns of said member and through said shock absorbing material, said shielding means including means for absorbing electromagnetic energy radiated by said member.

9. A device for receiving and delaying waves of electromagnetic energy, comprisin an elongated member, formed of a material having a dielectric constant substantially higher than air, and having an electrically conductive layer on opposed surfaces thereof and having a substantially helical form; means for launching an electromagnetic energy wave within said member affixed to at least one end thereof; a metallic container disposed about and completely surroundingsaid member, Said container having an outer portion and an inner portion each extending longitudinally of said member and spaced from the outer and inner surfaces thereof respectively; a shock absorbing material surrounding said member and disposed within the inner and outer portions of said container, said shock absorbing material substantially filling the space between said outer and inner portions and defining openings between adjacent turns of said member; and metallic shielding means disposed within said openings for inhibiting interaction of electromagnetic waves which may extend from said adjacent turns.

lit. A device for receiving and delaying waves of electromagnetic energy, comprising: an elongated member, formed of a material having a dielectric constant substantially higher than air, and having an electrically conductive layer on opposed surfaces thereof and having a substantially helical form; means for launching an electromagnetic energy wave within said member affixed to at least one end thereof; a metallic container disposed about and completely surrounding said member, said container having an outer portion and an inner portion each extending longitudinally of said member and spaced from the outer and inner surfaces thereof respectively; a shock absorbing material surrounding said member and disposed within the inner and outer portions of said container, said shock absorbing material substantially filling the space betwen said outer and inner portions and defining openings between adjacent turns of said member; a mixture of silver and a carbon base compound substantially filling each of said openings whereby each turn of said member is shielded from adjacent turns thereof and e'lectrornagneiic energy radiated from said member is absorbed.

References Cited by the Examiner UNITED STATES PATENTS De Rosa 333-31 Rumsey et a1. 33384 Tiley 333-31 Hebenstreit 33331 Grieg et a1. 333-84 10 Adams 333--84 Fox 33395 X Sabaroff 333-79 Arditi 33384 Lovick.

Lewis 333 -31 Germain 33379 Barrett 333-79 HERMAN KARL SAALBACK, Primary Examiner.

E. JAMES SAX, Examiner.

Claims

1. A DEVICE FOR RECEIVING AND TRANSMITTING WAVES OF ELECTROMAGNETIC ENERGY, COMPRISING: AN ELONGATED MEMBER, FORMED OF A MATERIAL HAVING A DIELECTRIC CONSTANT SUBSTANTIALLY HIGHER THAN AIR, AND HAVING AN ELECTRICALLY CONDUCTIVE LAYER ON OPPOSED SURFACES THEREOF AND HAVING A CONVOLUTED FORM SUCH THAT AT LEAST FIRST AND SECOND PORTIONS OF SAID MEMBER ARE DISPOSED IN SIDE-BY-SIDE ADJACENCY; MEANS FOR LAUNCHING AN ELECTROMAGNETIC ENERGY WAVE WITHIN SAID ELONGATED MEMBER AFFIXEAD TO AT LEAST ONE END THEREOF; SHIELDING MEANS DISPOSED BETWEEN SAID FIRST AND SECOND PORTIONS; AND A MATERIAL FOR ABSORBING ELECTROMAGNETIC ENERGY RADIATED FROM SAID ELONGATED MEMBER DISPOSED UPON AT LEAST A PORTION OF THE SURFACE OF SAID SHIELDING MEANS ADJACENT SAID ELONGATED MEMBER.