US2754513A - Antenna - Google Patents

Description

y 0, 1956 G. J. E. GOUBAU 2,754,513

ANTENNA Filed Dec. 4, 1951 2 Sheets-Sheet 1 Fri 2.

IN V EN TOR.

ATTORNEY July 10, 1956 G. J. E. GOUBAU 2,754,513

ANTENNA Filed Dec. 4, 1951 2 Sheets-Sheet 2 Fig.7.

Fig. 5.

I: Fig.3. 41.5,

IN V EN TOR.

Gemy ([5 Goubau BY United States Patent ANTENNA 'Georg J. -E. Goubau, Long' Branch, J., assignor to the United States of America :as represented by the 'Secretaryoftthe Army Application'December 4, 1951,"SerialN0. 1259;875

9' Claims. (Cl. 343-461) (Granted under Title 35,- U.-S. Code(1952), sec. 26.6)

This invention may be manufactured-and used by or for .the Government 'for governmental purposes without thepayment to me of any royalty thereon.

This invention relates to antennas 'for'use with surface wave transmission lines.

The surface wave transmission line, which ,is fully described in my patent application, Ser."No. 1511025, filed March 21, 1950, now Patent 2,685,068, issued July 27, 1954, has a broad field of utility in the transmission of radio energy. The presenttinvention relates toantennas for transforming electromagnetic surface wave energyto polarized wave energy for space radiation. 'These "antennas, which are utilized at the microwave frequencies encountered in surface wave transmission 'line applica- "tions, are designed to radiate electromagneticenergy-in {space at an angle to thetransmissionline. 'Severakmddifications provide a beam .of energy narrow in azimuth while other modifications provide omnidirectional-radiation in .a narrow vertical sector. "The first mentionedantennas may be rotated for use inscanning with the narrow ibeam ofenergy. The use of a surface wavetransmission 'line as the antenna mastobviates the needjof aseparate antenna. feed system.

It is therefore an object of this invention to provide antennas for transmitting and receiving electromagnetic wave energy for use with surface wave transmission lines.

It is another object of this invention to provide a highly .directive reflector type antenna for use with a surface wave transmission line.

It is a further object of this invention'to' provide a directive antenna for asurface wave transmission line'wherein different surfaces of-the antenna are axially spaced one half wave length along a surface wave transmission 'line.

It is yet afurther object ofthis invention to pr'ovide an antenna for a surface wave transmission line that transforms electromagnetic wave energy in a non-radiating mode to electromagnetic energy in a radiating mode.

.It is stillanother object of this invention toxprovide an antenna system that generates a scanning beam of electromagnetic energy.

Itisyet another object of this invention'toprovide an Iantenna for use with a surface wave transmission line that .utilizes spaced stubs-t terminate the line.

These and further objects of this invention willbe "more fully understood-when the following description is read inconnection with the accompanying drawingin which:

Figure l'illustrates one form of the invention in aparitially. sectioned elevation;

Figurel shows the antenna reflector plates of Figure 1;

Figure '3 isa diagrammatic sketch for'use in the expla' nationof 'the operation of the invention;

Figures '4 through 8 are modifications of theinvention shown in perspective; and

Figure '9 is a further modification of the invention in (elevation.

In general terms, this invention comprises placing an .antennaon a surface "wave transmission line so that the energy that is being propagated along the line will'be ice 2 :radiated at 'an angle to .theline. This isiaccomplis'hed "either by:reflection or bytheuse of radiating stubs spaced axially "and'horizontallyalong the transmission line.

Examining Figures 1 and 2 in detail, a surface 'wave transmission line 1 is shown connected to a suitable launching device 2, in this instance shown as a horn. -Meansfor launching the electromagnetic energy upon line 1 are described in detail in my above referred to patent. The energy propagated by the line, which will be referred totherein as surface wave electromagnetic energy, is wave energy in a non-radiating mode as isfully explained in myabove referredto application. Located on line land preferably terminatingthe line is a directional antenna preferably formed .by semi=elliptical plates 3 and 4. Such plates are metal for optimum 'antenna efiiciencyalthou'gh other materials including dielectric material may be uti -lized if.a lowerantenna efficiency is desired. 'For example, if adielectric material is usedand the plates positioned on a line, aportion of the wave energy willbe reflected and aportion'will continue along the line. It can -be'seen that this type of operation makes possible any desired radiation pattern by selectively positioning several reflecting antennas along the line at various angles to the line.

Plates Sand '4 are positioned by a supporting member 5 shown in Figure *1 constructed of insulating material. However, the supportS may "be metallicin nature, it desired-for additional'streng'th. 'It is obvious that member 5 could'be formed in-a'variety of ways, the showingbeing illustrative only. Supporti "has a bearing surface6 so that 'it may berotated, with"the'line as'theaxis of rotation, by a-rotator 9. Plates 3 and 4are arranged at an angle-with the line, hereshown as 45 degrees, and axially spaced along-the line. It is to be understood that the invention is not limited to any specific angle of the plates with the line, 45 degrees being illustrative only. The amount of spacing is determined by the wave length of the electromagnetic waves, being in all cases, for optimum operation, one halfthe wave length of thepropagated energy. However, it is to belunderstood that some de- Viationfromthe specified 0ne-half wave length spacing :may be made .without rendering the system inoperative.

The plates Sand 4 do not contact the line but are separated therefrom due to cut out portions 7 and 8 shown in Figure 2. The size ofplates 3 and 4 is determined by the radius of the field-aboutline 1, which is dependent upon the wave length being utilized and the surface conditions of the'line. For optimum operation of the antenna system, the reflecting plates 3 and 4 should be approximately the same size as the field'of the surface waves propagatedalong line 1 to provide proper illumination of plates 3 and 4 by'the electromagnetic field.

'The plates are preferably semi-elliptical since theprojection of these plates normalto the lines will belaicircle. Such aconfiguration provides a narrowconical beam of energy which isdesirable. 'For example, with one experimental antenna a beam of Wave energy of 2 degrees width, as normallydefined, was obtained. It is of course obvious that various shaped plates may be used to provide beams "that have different characteristics, and if the plates are .at angles other than 45 degrees to the line, their shape will have to be altered accordingly.

The operation of the system will be explained withparticular reference being made to Figure 3. Surface wave electromagnetic energy that is traveling along line 1 is indicated by lines ,9 with arrow heads showing the direction of energy propagation. This wave energy will encounter reflecting plates 3 and 4 and be radiated therefrom in the direction indicated. The electric field of the surface wave energy can be.though of as a number of radial'E lines about line :1. It can be seen that if plates '3and-4 were not-aXially-spaced, the wave energy reflected therefrom would not be properly polarized since the wave energy E line components from plate 3 that are in the plane of the paper would be 180 degrees out of phase with similar E lines of the energy reflected from plate 4. Therefore, the two antenna plates are spaced one-half wave length to provide a suitable phase shift. By following the path of wave energy from line a-b, the principle of operation will be clear.

The wave energy a-b, upon travelling to plate 3, will be reflected and after a certain period of time arrive at line cd. This same wave energy on the opposite side of the line will, during the the same period, be reflected from plate 4 and travel to line ef, one half wave length from line ca'. At this instant, the E line components, in the plane of the paper, of the wave energy at line c-d will be 180 degrees out of phase with similar E lines at 2- However, it is well known that in one half wave length of travel, the electric field reverses phase 180 degrees. Therefore, when the wave energy from e-f travels to cd, the E lines will be 180 degrees reversed in phase and consequently in phase with the E lines of energy reflected from plate 3. It is easily seen that the components of the E lines that are perpendicular to the plane of the drawing will cancel. Thus, vertically polarized electromagnetic wave energy will be propagated by this antenna arrangement.

Stated more simply, the half wave length spacing between the antenna plates is for the purpose of providing electromagnetic wave energy, reflected from plates 3 and 4, having cophasal electric fields.

This embodiment and the below described embodiments of the invention may be utilized for receiving as well as transmitting antennas. Thus, electromagnetic wave energy from space that impinges upon an antenna in accordance with the invention will be transformedto surface wave energy for the same reasons the reverse action is true. In other words, the transforation phenomenon discussed above is reversible.

Fig. 4 is a modification of Fig. 1 and operates in substantially the same manner except that the polarization of the propagated wave energy is 90 degrees rotated from the polarization of the energy radiated by, the antenna of Fig. 1. This is due to the different orientation ofthe antenna reflecting plates. The antenna of Fig. 4 consists of plates 16 and 11 positioned at an angle of 45 degrees with line 1 and axially displaced along the lineone half wave length. These plates are preferably positioned by a support 12 which is free to rotate about the line in the same manner as described in connection with Fig. 1. It is of course obvious that various other types of supports could be utilized, the specific embodiment being illustrative only.

Figs. and 6 illustrate another modification of the invention. In this modification, in place of the two reflector plates previously described, a single helical plate is utilized. This plate is preferably at an angle of 45 degrees with the line and is positioned by a support 22, which is free to rotate. The extremities of the plate are spaced one quarter wave length axially on the line for the purpose more fully set forth in. connection with Fig. 1. If the analysis of Fig. I is applied to this modification, it will be seen that a circularly polarized wave will be radiated by the antenna. The plate 20 is preferably shaped substantially elliptically, so that the projection of the plates normal to the line 1 will be a circle.

Such a configuration will provide a sharp conical beam Plates and 33 are spaced 7 so I V the invention.

general shape of the reflector plates is preferably elliptical so that the projection of the plates will be a circle. If the analysis of Fig. 1 is applied to this modification, it will be seen that this configuration will radiate circularly polarized wave energy.

It is to be noted that the lower reflecting surfaces in 7 Figs. 4, 5, 6 and 7 are of a different configuration than the upper surfaces. This difierence is due to the half wave spacing between the reflecting plates which makes necessary the use of dissimilarly shaped plates if a true circle projection of the reflecting surfaces is desired.

Another modification of the invention is illustrated in Fig. 8. The antenna comprises a reflecting cone terminating line 1. The surface wave energy will be reflected as vertically polarized wave energy in a narrow vertical sector over 360 degrees of azimuth.

It should be noted that all spacings are measured in wave length of the guided wave energy. Usually the diflerence between free space wave length and wave length on the guide is small, an exception being the modification described below. In this case, the wave length on the antenna section is considerably smaller than the free space wave length. V I 1 Figure 9 shows another modification of the invention. Line 1 is connectedto a conductor 40 to which stubs 41 are joined. A terminating element 42 may be employed to cap the conductive line 40 so that the wave energy traveling from line 1 proceeds along section 40 as a traveling wave. Stubs 41 spiral about the section 40 to provide points of discontinuity from which the wave energy is radiated, such energybeing horizontally polarized. In the most general case, the, displacement in degrees wave length of two consecutive elements 41 along the line is equal to the displacement in degrees phase angle about the line. In the arrangement illustrated, these stubs are spaced along the line at degree intervals, i. e., a quarter wave length, and are displaced horizontally by 90 degrees phase angle about the line. More or fewer stubs may be employed so long as they are spaced according to the above described pattern. For example, if the phase angle between two consecutivestubs about the line is 50 degrees, the distance between the'stubs along the line is I a 50A Where is the wave length on section 40.. This antenna .will radiate energy omi-directionally in a narrow vertical i been particularly described and illustrated, it will be understood that various other modifications and improvements, may be made without departing from the spirit of Therefore, it is not desired that the invention be limited to the precise details set forth.

' What is claimed is:

1. A microwaveantenna system comprising. aplurality of reflecting surfaces and a surface wave transmission line, said surfaces being positioned around said line and being disposed at,an angle with said line, said surfaces .taken in combination being substantially elliptical and said surfaces being axially displaced from each other a total of one half wave length. V

2. A microwave antenna system for electromagnetic energy of a predetermined frequency comprising an elongated conductor having a surface conditioned to slightly reduce the phase velocity to concentrate the field of the energy near the conductor in a non-radiating ,mode,

7 launching means coupled to said conductor for producing between them. The supports for these plates have'bee'n omitted for purposes of clarity but manytake the'form a of the supports illustrated in Figs; 1, 4 or 5. Again the a field distribution which matches the field distribution on the conductor, directional antenna means positioned along said conductor at a point spaced from said launching means and ,illuminatedby said .field for converting said nonradiating mode to a radiating mode, and means for rotating said directional antenna about said conductor. 3. A microwave antenna system for electromagnetic energy of a predetermined frequency comprising an elongated conductor having a surface conditioned to slightly reduce the phase velocity to concentrate the field of the energy near the conductor in a non-radiating rnode, launching means coupled to said conductor for producing a field distribution which matches the field distribution on the conductor, directional antenna means positioned along said conductor at a point spaced from said launching means and illuminated by said field for converting said non-radiating mode to a radiating mode, said directional antenna being formed by a plurality of surfaces for reflecting electromagnetic wave energy, said surfaces positioned around said conductor and disposed at an angle to said conductor sdthat said electromagnetic energy is radiated by said surfaces at an angle to said conductor.

4. A system as defined in claim 3 which includes means for rotating said antenna about said line.

5. A microwave antenna system for electromagnetic energy of a predetermined frequency comprising an elongated conductor having a surface which slightly reduces the phase velocity of the energy to concentrate the field of the energy near the conductor in a non-radiating mode, launching means coupled to said conductor for producing a field distribution at said predetermined frequency which matches the field distribution on the conductor and radiating means having a plurality of reflecting surfaces positioned along said conductor and spaced from said launching means and illuminated by said concentrated field for converting said non-radiating mode into a radiating mode at said radiating means.

6. An antenna system as in claim 5 wherein said surfaces are positioned around said line and being disposed at an angle with said line, said surfaces being axially displaced from each other.

7. A system as defined in claim 6 wherein said angle is degrees.

8. A system as defined in claim 6 which includes means for rotating said reflecting surfaces about said line.

9. A microwave antenna system for electromagnetic energy of a predetermined frequency comprising an elongated conductor having a surface conditioned to slightly reduce the phase velocity to concentrate the field of the energy near the conductor in a non-radiating mode, launching means coupled to said conductor for producing a field distribution which matches the field distribution on the conductor, directional antenna rneans illuminated by said field for converting said non-radiating mode to a radiating mode said directional antenna comprising a plurality of reflecting plates mounted at a predetermined angle to said conductor, said plates being spaced along said conductor, said'spacing along the conductor being directly proportional to the radial displacement of the plates from one another around said conductor so that said spacing along the conductor will be substantially one half wavelength at radial displacement between any pair of plates.

References Cited in the file of this patent UNITED STATES PATENTS 1,931,980 Clavier Oct. 24, 1933 2,298,449 Bailey Oct. 13, 1942 2,438,795 Wheeler Mar. 30, 1948 2,542,844 Smith Feb. 20, 1951 2,575,058 King Nov. 13, 1951 2,588,610 Boothroyd et al Mar. 11, 1952 2,595,271 Kline May 6, 1952 2,595,912 Alford May 6, 1952 2,599,705 Erwin June 10, 1952 2,659,817 Cutler Nov. 17, 1953

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