US2599895A

US2599895A - Eta-plane horn

Info

Publication number: US2599895A
Application number: US641606A
Authority: US
Inventors: Chu Lan Jen
Original assignee: US Department of Navy
Current assignee: US Department of Navy
Priority date: 1946-01-16
Filing date: 1946-01-16
Publication date: 1952-06-10
Anticipated expiration: 1969-06-10

Description

June 10, 1952 Filed Jan. 16, 1946 FIG.I

FIGEB INVENTOR LAN JEN CHU ATfORNEY Patented June 10, 1952 H-PLANE HORN Lan Jen Chu, Brookline, Mass., assignor, by mesne assignments, to the United States of America as represented by the Secretary of the Navy Application January 16, 1946, Serial No. 641,606.

1 V This invention relates in general to high frequency directive energy transmission and reception, and more particularly concerns the novel structure of an electromagnetic horn of improved radiation characteristics. 7 I

An electromagnetic horn comprises, broadly, a flared conductive radiator used for the interchange of wave energy between space and a transmission line and provides a directive or sharply defined radiation pattern. The field pattern obtained by the use of a horn at a particular frequency is a function of the shape and dimensions of the major opening or horn aperture which in turn is determined by the flare angle and horn length. The horn is coupled to a transmission line at the constricted or throat end thereof. 'I'hedirectional properties of the horn are the same for transmission or reception, and the directivity may be effectively increased by the addition of a reflector.

In various applications a horn radiator introduces undesirable features. As an example consider the representative problem of a low angle, or surface search radar system which utilizes a horn for the transfer of energy between a transmission line and a reflector, which in turn provides-a radiation pattern with a principal lobe directed toward the horizon and parallel to the earth. The use of a conventional horn radiator results in an overall radiation pattern which in-- cludes undesirable side lobes, also parallel to the surface of the earth and at right angles to the principal lobe. Although the energy content of the right angle lobes is considerably less than that of the major lobe, these side lobes will pro-- duce on an indicator incorrect and confusing target indications. It is therefore a specific object of my invention to provide an electromagne'tic. horn. radiator having a field pattern including a principal lobeand side lobes oriented such as to eliminate substantially all spurious response. 1

Anotherobjectof my invention is to provide an electromagnetic. horn radiator of asymmetrical structure.

A further object of my invention is to provide a hornradiator which in combination with .a reflector produces an overall radiation pattern comprising a sharp, directional principal beam and minor side beams elevated with respect to the principal beam.

These and other objects of my invention will now become apparent from the following detailed specification taken in connection with the. accompanying drawings in which:

7 Claims. (Cl. 250-3315) 1 surface; and

Fig. 3 illustrates the radiation pattern of the horn radiator illustrated in Fig. 2 in a plane Fig. l is a general perspective view of the novel electromagnetic horn of my invention;

Fig. 2 illustrates diagrammatically the combination of the horn of Fig. 1 and a reflecting passing through the axis IIIIII of Fig. 2-andnormal to the plane of Fig.2.

Referring now to Fig. 1, there is illustrated an electromagnetic horn embodying the principles of my present invention. This horn structure comprises essentially a transmission line extension or input end ll of substantially rectangular cross section, adapted for coupling to a corresponding rectangular wave guide transmission system (not shown). The longitudinal axis I2 of the rectangular input section ll comprises also the axis of the horn l0 and indicates the direction of en'- ergy transmission therethrough. The horn I0 is a pyramidal conductive structure extending from a rectangular throat-section l3 at the junction with input section II to a comparatively large rectangular aperture M. This flared section is} constructed of four substantially trapezoidal metallic plates, two of which l5 and I6 are narrow and the other two of which I! and I8 are comparatively broad.

erture I 4 of the horn is fixed in non-perpendicular relationship with the axis I2 of energy prop-' agation through the horn. The angle between the plane of aperture l4 and the normal to the axis I2 is designated as angle 0 on the drawing.

The angle between the plane of the rectangular throat l3 and the normal to the axis I2 is also made equal to 0, thereby permitting the broad walls [1 and [8 to be plane trapezoids rather than warped surfaces. 1

The horn illustrated in Fig. 1 may be utilized to interchange energy between a transmission line and space. For example, if the horn is utilized in a transmitter system, energy coupled thereto I at rectangular input section II will be radiated from the rectangular aperture It. If the horn is utilized in connection with a receiver, energy intercepted by the aperture [4 will be delivered to the transmission line section coupled at section I I. Energy radiated from the horn of Fig. 1 is directional in nature, and the directivity thereof is primarily a function of the flare angle of the born between .the throat section l3 and the aperture M. For the pyramidal horn, as illustrated in Fig.

.' 1, the. flare angleinthe vertical plane is greater 1 is electromagnetic in nature and includes an; electric field component which is parallel tothe.

narrow walls l5 and I6 thereof, and normal to the axis l2. The electric field vector is,; graphically illustrated at 2|.

is normal to both the electric fieldcomponent 2i and the axis of propagation l2.

It will be noted that the horn ID has .anasymmetrical cross section in -a plane taken through theaxis l2 and the m agn etic;field vector :22. The improved performance ofthe horn l0 resultingfrom theasymmetrical construction thereof willnqwjbe discussed in connection, with the. diagrammatic representation of an antennasystem illustrated-inFig, 2. As-illustrated the horn-Ill is;attached, at rectangular coupling-section H, to, a;corr esponding rectangular wave guide-transmission system 3| suitably supported hyapparatus; not shownin the drawing. The axis 12 is directed at 7 angle 0 with respect vto the horizontal to acentral point of aparabolic reflector SZsecuredto an antenna pedestal-33. Theparticular ,system illustrated comprises the basic antenna requirement forasurface or low-, -angle search radar and provides .a radiation pattern having a. principal lobe 34 directed so; that -rnaximum .intensity is obtained in a beam parallel to thesurface of theearth or .sea. A conventional horn, having an aperturecut in a plane normal to .theaxis of energy transmissionhas side ,lobes due to direct radiation-fromthehorn 'in -,a ;plane common to the principalllobe' and the .liornaxis. .The explanation of this lies. in the substantially in :phase relationship of the aperture illumination ,which maybe .thusconsidered as an effective broadside radiator producing a beam normal to the long edges. Thus side lobes displaced 90 from the horn axis are direc fid, atthe horizon. If the principal beam andside lobes of asearch radar are all parallel tothe earth's surfacetargetechoes will produce multiple and. confusing indications .despite.-th e.

smaller energy content of theside lobes.

Eor t e as mme ca hor structure of, F g. 1 1 sec in a ic te i .2 .th hasep t aper ur l um a io is u orml va iab u t th .q res ond ne un or var a i n o istanc b w en points alone a ze ss an th displaced 90 from the horn axis ,areelevated abovegthe horizon.

=Eig.-3 illustrates thcside lcbes: :3-and fifik fil l r ated asa result of. currentsin;.th e'.\5v ttica-lly posietioned;edges of .the'hormlii shown in Figl 2. The

plane of these side; lobes corresponds :to the .plane,

of the aperture M, the aperture Ibeing shown in Fig. -3 for clarity. These side .lobes i ifiand M are-directed abovethe horizontal :by .an;.angle10,

and are compared with the'horizontalsidelobes 4|- and LIZ whichwould beobtained-.ifthe aper-1 ture of the horn were 'cut normal to the "axis The .magnetic :field. come ponem; may be represented by avector :22 which thereof. By thus raising the side lobes of the radiation pattern, the aforementioned spurious, multiple response is eliminated in surface search equipment.

A more general analysis of the radiation pattern of the horn l0 indicates that maximum energy is radiated therefrom along the axis l2 aspreviously described. Energy is also radiated in.other directions including the sidelobes '43 and 44, and the locus of the vector indicatin peak energy radiation in a particular direction forms, essentially, a conical surface generated about the vertical axis .IIIIII, illustrated in F 'ig. 2 withvthecenter of the aperture M as the 1'5.

vertex. Whenth horn is oriented in the manner illustratedin Fig. 2, peak radiation is horizontal only for theprincipal lobe 34 and all other radiation is above the horizontal as desired for ,the specific radar application described above.

It is evident that the asymmetrical horn structure need not be limited .to the particular pyramidal design illustrated .in Fig. 1. The flare angle and the aperture size will in each instance.

be determined by-the application. of the'radiator structure. Horns of othercr-oss sectional configuration and other electrical feeds maybe utilized to,provide similar results .if'the'principles described above are followed.

Thus, since various modifications andextjen sions of the principles hereinabovese t forth will be evident to those skilled in the art, .I prefer that thespirit and scope of the present invention-be defined not by thesespecific disclosures but by the appended claims.

Whatis claimed is:

l. Anielectromagnetic horn for interchanging energy between a transmission line .and'space, said horn comprising a,flar,ed conductivfeistruce ture terminating in .an aperture at one .end

thereof and a constricted throat'sectionat the opposite end thereof, said aperture and said throat section substantially lying in parallel planes in non-perpendicular relation with the axis of-said -horn.

v2. A n.electromagnetic radiation system com,- prising a waveguide terminating in an aperture, a flared horn having its'axial extremitieslying inparallel planes, thesmaller of said extremities, being identical to and continuous with the aperture in-said'wave guide, and the parallel-planes determined by said axial extremities beinggi n one e cu a w elafion hipw th :the lon iprising, in combination, a reflector, a wave guide. 1 and a flared horn integral with'said wave guide illuminating said reflector, the junction of said horn withsaid waveguideand the 'te'rmination of said horn lying in parallel -planes"- in non-perof said waveguide.

pendicular relationship-with-the longitudinal axis 5. A directional antenna system for-the-trans mission and reception of; a. beam of energy compris ng, inJcombination ,a reflectoij a wave guide having its longitudinal axis-angularly displaced from the axis' of l said beam' 1 or --energy, aefiarea horn having its smaller end integral with the end of said wave guide, both smaller and larger ends of said flared horn lying in parallel planes in non-perpendicular relationship with the longitudinal axis of said wave guide.

6. A directional antenna system comprising, a. parabolic reflector for forming a substantially pencil-shaped beam of energy, a rectangularwave guide, and an electromagnetic horn of conductive material formed by flaring out the walls of said wave guide, the junction of said wave guide and one extremity of said horn comprising a rectangular aperture, the opposite extremity of said horn comprising a larger rectangular aperture lying in a plane parallel to the plane of said first-mentioned rectangular aperture, said and third parallel planes, said transmission line being joined to said electromagnetic horn in said second plane, said second and third planes being nonperpendicularly related to the axis of propagation of energy in said electromagnetic horn. said axis of propagation of energy being a continuation of the axis of said transmission line and being. at an acute angle to saitf'first plane.

LANJEN CHU.

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

UNITED STATES PATENTS Number Name Date 2,283,935 King May 26, 1942 2,362,561 Katzin Nov. 14, 1944 2,364,371 Katzin Dec. 5, 1944 2,369,808 Southworth Feb. 20, 1945 2,407,068 Fiske et al. Sept. 3, 1946 2,423,073 Willoughby June 24, 1947 2,436,408 Tawney Feb. 24, 1948 FOREIGN PATENTS Number Country Date 495,977 Great Britain Nov. 23, 1938