US3202997A - Scanning corner array antenna - Google Patents

Description

Aug. 24, 1965 A. c. SCHELL 3,202,997

SCANNING CORNER ARRAY ANTENNA Filed Oct. 16. 1961 5 Sheets-Sheet 1 INVENTOR. HAMA/Y l @6V/16,6

Aug. 24, 1965 A. c. SCHELL 3,202,997

SCANNING CORNER ARRAY ANTENNA Filed Oct. 16, 1961 5 Sheets-Sheet 2 Aug. 24, 1965 A. c. scHELL SCANNING CORNER ARRAY ANTENNA 5 Sheets-Sheet 3 Filed Oct. 16, 1961 INVENTOR. H664 C. 527145616 ULM da( uw l?. 711

A. C. SCHELL SCANNING CORNER ARRAY ANTENNA Aug. 24, 1965 5 Sheets-Sheet 4 Filed Oct. 16, 1961 INVENTOR. /V 6. STA/l LUL@ Aug. 24, 1965 A. c. SCHELL 3,202,997

SCANNING CORNER ARRAY ANTENNA Filed OCT.. 16, 1961 5 Sheets-Sheet 5 UMD MMR. 711 m79 United States Patent O 3,?.ti27 SCANNING CORNER ARRAY ANTENNA Allan C. Schell, Medford, Mass., assigner to the United States of America as represented by the Secretary of the Air Force Filed Giet. 16, 1961, Ser. NdT-45,519 3 'Claims (Cl. 343-814) (Granted under Title 35, US. Code (1952), sec. 266) The invention described herein may be manufactured and used by or for the United States Government for governmental purposes without payment to me of any royalty thereon.

'i his invent-ion relates generally to apparatus for radiating and receiving ultra high frequency electromagnetic waves, and more particularly to a directive, corner reliector antenna system whereby scanning within the corner may be accomplished without physical movement of the reector structure.

The corner reector antenna has many characteristics which make it an attractive means for transmitting electromagnetic waves. These characteristics include high gain, low back radiation, good directivity, wide bandwidth, and constructional simplicity. The use of such an antenna, however, has been limited to applications where the dimensions of the reflector aperture approximate one or two wavelengths, and the corner angle is either sixty or ninety degrees. A further vexing, and heretofore unsolved problem, is the mechanical diiiiculty encountered 4in scanning with this type of antenna. Due to the large size of the corner antenna, especially at frequencies on the lower end of the radio spectrum, physical movement of the antenna structure is extremely difficult.

Because of the limited utility of the conventional corner reflector antenna, various alternate schemes are resorted to whenever more directivity and gain are desired, or whenever specifications call for a particular beam conliguration. The most common of said alternate schemes are the horn antenna, the parabolic reector antenna, and the dipole array antenna. All are more diicult to construct than the corner reiiector antenna, and are consequently more expensive. The horn antenna has the additional disadvantages of being inliexible, and extremely large at low frequencies. The dipole array antenna is subject to high back radiation and is, therefore, unsatisfactory for most military applications. The consequent increase in physical size of each of these antennae with the reduction of frequency, as in the case of the corner reflector antenna, accentuates the problem of moving the large structure for scanning purposes.

In my co-pending patent application entitled Corner Array Antenna, Serial No. 24,184, now abandoned, l have disclosed a novel corner reflector antenna in which there is placed a plurality of dipole feed elements disposed at discrete points along the bisector of the corner angle. The design of a corner antennae of greatly enhanced utility having any desired beam configuration is made possible by the principles taught therein. The present invention is a further improvement on the corner angle reflector antenna, whereby the problem of scanning with large cumbersome antenna structure is effectively resolved.

lt is accordingly the primary object of my invention to provide a corner reiiector antenna capable of scanning within the area defined by the reflecting surfaces without physical movement of the antenna structure.

lt is another object of my invention to provide an ultra high frequency antenna of simple construction having high gain, a high degree of directivity, wide bandwidth, Aa steerable beam, and low back radiation, said antenna being adaptable to a wide range of applications.

lt is still another object of my invention to provide a novel corner reector antenna having a wider range of application and greater utility than has heretofore been possible.

it is a still further object of my invention to provide a corner reflector antenna having a high degree of directivity and gain.

lt is a still further object of my invention to provide a corner refiector antenna adapted to produce substantially any speciiied beam configuration in combination with means for sweeping said beam within the confines of said reflecting surfaces.

It is a still further object of my invention to provide an ultra high frequency electromagnetic wave antenna cornprising a corner reiiector structure in combination with a multiple dipole feed.

it is a still further object of my invention to provide means for radiating a high frequency electromagnetic wave, said wave having a narrow beam width, low sidelobe pattern commensurate with the size of the antenna.

These and other objects and advantages of the present invention will become more apparent by reference to the following description taken in conjunction with the accompanying drawings in which:

FIG. l illustrates a 60 corner angle reilector antenna having a plurality of dipole feed elements disposed at discrete points along the bisector of said corner angle;

FlG. 2 illustrates the field pattern produced by said 60 corner angle reflector antenna;

FlG. 3 illustrates the vertical field pattern produced by said 60 corner angle reiiector antenna;

FIG. 4 illustrates azimuthal field patterns produced by said 60 corner angle reflector antenna taken at elevation angles Of p:l5, 115:30?, q5:45 and I60 FlG. 5 illustrates the components of an olf-axis beam in a corner angle reiiector antenna for the values Fw),

FlG, 6 illustrates a corner angle reliector antenna adapted to produce a field pattern having sine terms;

FIG. 7 illustrates a 60 corner angle reflector antenna adapted to steer the beam produced thereby within said corner angle;

FlG. 8 illustrates the radiation pattern of said steerable `beam at beam position -0, 0:5", =lG, 0:15", and 02200;

FiG. 9 illustrate apparatus for controlling the directivity of said beam; and

FIG. l() illustrates an isometric view of one embodiment of my invention.

My aforementioned co-pending patent application presents the `analysis of the corner antenna field pattern as a consideration of the reiiections of a plane wave incident upon the corner. A means for obtaining narrow-beamwidth low-sidelobe patterns commensurate with the size of the antenna, said means involving the use of a number lof feed elements located along the bisector of the corner angle, is disclosed therein. These elements produce higher-order terms of angular variation of the radiation pattern, and allow the synthesis of desired symmetric functions.

My present invention discloses, as an improvement thereon a novel means for producing sine terms in the radiation pattern of a corner reector antenna. l have discovered that, by the proper combination of sine and cosine terms, it is possible to produce a narrow beam at substantially any angle within the corner angle. The sidelobes can be kept low during the beam-steering. This technique affords a method of electronic steering of a lowsidelobe narrow beam within the sector angle.

The equations and their solutions for the electromageos qw] cos 90+.94J15(17.2 cos 4 eos 156) netic fields generated by the subject corner reflector antennae disclosed herein are expressions representing the inter-relationship of beam configuration, reflector geometry, number and position of feed elements, phase and magnitude of the current on feed elements, and frequency. General and specific application of these expressions will be illustrated whereby the several objects of my invention are accomplished.

In the following calculations of eld patterns, the reflecting surfaces of the corner are considered to be planar, perfectly conducting, and innite in extent. rThe angle between the two planes comprising the corner is chosen to be a submultiple of 180, or 1r/N radians. The polarization of the transmitted or received wave is such that the electric eld vector is parallel to the line of intersection of the two planes, denoted by the z direction. Symbolically, the corner angle isn/N, the distance from the apex to the feed elements is r, the elevation angle is p, the azimuth angles is 0, k is Zw/A, and ]n(kr) is the Nth order Bessel function.

Under these conditions, the far field produced by a single current element located at a point on the bisector of the corner angle is The extent to which a particular current generates one of the terms of this series is determined by the value of the corresponding Bessel function, and this is related to the distance of the elements from the apex in wavelengths. v

By placing several radiators along the bisector of the corner angle, it is possible to produce a radiation pattern of the form Ez-ZAmIm cos (2m-l-1)N0 (2) in the range -1r/2N01r/2N. In this manner, radiation functions even in 9, such as a narrow beam pointed along the corner angle bisector, can be synthesized. An estimate of the size of the conducting planes for a given beamwidth of a uniform illumination pattern is wavelengths between the edges of the ground planes, and

11:0.73 amps, [2z- 1.17 amps, and 13:0.94 amps respectively. Said dipoles are located on the bisector of said corner angle at the distances from the intersection of said reflecting surfaces.

rl`hese elements produce a beam with ZO-db uniform sidelobes in the H or azimuthal (=0) plane. It is necessary, however, to examine the radiation pattern at various elevation angles in order to be sure that there z are no large high-angle lobes. The complete description of the eld is given by the equation cos sin 6) cos qb Curve 22 of FIG. 3 presents a vertical cut through the radiation pattern of 6:0 t0 show the behavior of the main beam as a function of elevation angle.

This pattern illustrates the directivity obtained in the vertical plane as the result of adding elements for horizontal plane beamwidth reduction. The use of a number of elements along the bisector of the corner angle benefits principally the azimuthal or 6 plane pattern, but it should be remembered that the element positions may be chosen such that a desirable elevation pattern is also obtained.

The corner array thus has directivity in both planes and should not be considered a two-dimensional device. If additional colinearelements are used to narrow the elevation beamwidth, use should be made of the inherent properties of the corner. A considerable reduction in the number of necessary elements may result.

Azimuthal cuts through the radiation pattern for various elevation angles give additional information. First, any large, high-angle lobes can be found. Second, the frequency dependence of the pattern is shown. Apart from the element pattern, the elevation angle behavior of the corner array is contained in the Bessel function argument kr cos p. Thus, azimuthal plots for a range of values of rp with k held constant may also represent plots at a particular qb for different values of k (or A). The azimuth patterns for =0, 15, 30, 45, and 60 with )\=)\0 may also be viewed as plots of the azimuthal pattern at =0 or \0, 1.04k0, 1.160, 1.41% and 2k. The azimuthal patterns of the array in FIG. 1 are shown for elevation angles of =15, 30, 45, and 60 by curves 23, 24, 25, and 26, respectively of FIG. 4. The effect of the higher-order terms decreases with elevation angle; the pattern at =45, while reduced in magnitude, has broadened because of the phase reversal of the field component produced by the second element. The element impedances are of course also a function of frequency. Y

The radiation patterns described thus far contain only odd cosine functions of N 0, that is, they are of the form To produce sine terms in the radiation pattern it is necessary to position elements off the corner angle bisector.

The expression for the corner antenna field is valid only in the range -1r/ZNS0S1r/2N. The argument of the rstterm in the series, cos N0, varies between and +90". The restriction of zero field at the conducting surfaces prohibits even cosine terms in N0 from appearing; such terms would not be zero at ir/ZN. Similarly, any sine terms that are produced must have arguments that are even multiples of N0 because odd multiples would not go to zero at the conducting planes. The terms of angular variation of the radiation pattern are therefore odd cosines and even sines. These may be written as Ez(0)= Z Am cos mN-I-Z Bm sin mN0 In general, it is desirable to synthesize patterns that can be put in the form A n=o Harmonics other than those of N0 need not be considered, since the pattern exists only in the sector qr/N. If this function is reversed and displaced by ar/N, it may be written Taking the difference F(0)=20n cos nNtH- EDD sin nN (S) odd even From this it is possible to develop a workable beam synthesis. Given a complete Fourier series approximation of a desired function, the pattern obtained from the corner will be the difference between the complete series of argument 6 and the same series with the argument reversed and shifted by w/N. For example, consider the beam represented by curve 27 of FIG. 5. It may be represented by N 17(0):2 An cos nN(6-00) N N :E An cos nil/'00 cos MVM-; A, sin nN sin nNQ Forming the difference F(0)=%F(e)-F(1f/N-e N N :W24 A cos MVM-00) -ZAD cos nNr/Nl-O-w) n=l n=l ZA', cos nil/'90 cos nN-l- AEA, sin 71H0., sin nNH Odd even (1G) the feeding coefficients An are seen to be altered by cos nNo or sin nNo for the odd and even cases. The two patterns Fw) and -Frr/NMH) are represented by curves 255 and Siti, respectively and the result 1W( 0) is represented by curve of FIG. 5. This function is Zero atie/2N.

A narrow beam with low sidelohes at an angle 00 from the bisector of the corner, satisfying the conditions irnposed by the reflecting surfaces of the corner, can in this manner be obtained. By proper adjustment of the currents that produce the various terms a beam can be steered within the corner angle.

The current and radiation pattern relations having thus been determined, it is possible to position the various sine and cosine-generating elements. The odd cosine terms may be produced as previously described, 'that is, elements may be located along the bisector of the corner angle in such a manner as to produce the even part of the desired function. Elements placed along the bisector do not change the symmetry of the device and therefore generate no sine terms; however, if two elements of opposite polarity are symmetrically disposed on each side of the corner angle bisector, only sine terms will result. The production of sine terms within the corner is accomplished with element pairs and may therefore be done without involving the cosine-generating gelements. rThe first sine term needed is sin Zit/'0, and this suggests a corner of fr/ZN radians. 6 shows a method of producing the sin 2N0 term. Each of the two elements 33 and is located on the bisector of one of the angles formed by reflector surfaces and 323, and the corner angle bisector. The resultant pattern is the same as that of a corner angle of fr/ZN, oriented at an angle of M4N to the 0:0 axis. Since two elements are used, this pattern exists in the entire corner of vr/N. This may be written as The next term of the series that is excited by elements 33, 394 is sin 6N9; another set of elements is therefore necessary to produce a sin 4N@ term. This may be done by using four additional elements located at :hw/8N, i31r/8N, with adjacent elements oppositely phased.

ti Such a scheme has the distinct advantage that no other lower-order terms are produced, that is, four elements properly located along an arc generate sin 4N6, sin 12h70, and the feeding coeflicients for these elements need not involve other terms,

The foregoing theory and concepts may now be applied to the design of a scanning corner array antenna in accordance with the principles and objects of my invention, a specific embodiment of which is illustrated in FlG. 7.

The antenna design is developed from a determination of the LFourier components of the corner reflector fields. The corner angle specied is 60, and five terms of the antenna pattern are to be generated. These are cos 30, sin 66, cos 95, sin 120, and cos 150. As the beam is steered within the sector, the feed currents must be varied Iaccording t0 the beam angle. The elements of the array as illustrated in FlG. 7 comprise reiiector surfaces 35 and 36, and dipole feed elements 37 through 45. The distance r from the apex is chosen for each dipole feed element so that the Bessel function associated with the .particular field component is near a maximum, yand the other terms are small. In the present example r1=.64 t, @21.20% r3=l.58 r4=2.23h and r5=2.79?\. The angular variation of the field pattern associated with each element is such that Il, i3 and I5 excite cos 39 cos 90, and cos l5@ tennis respectively, I2 excites the sin 60 term, and I4 excites the sin f2.6 term. The elements that produce the sin 126 pattern are interconnected so that only one cable is used for the control of this component. The same is true of the sin 60 pair. The manner in which the feed currents are varied in order to produce a beam oriented at dincerent angles is given in the following feed coeicient table. The radiation patterns corresponding to these beam positions are illustrated by curves 46 through Si) of FIG. 8.

Feed Coecent table Beam Position 0 Cos 3 Sin 60 Cos 90 Sin 120 Cos 156 (C1) (Dz) (Cs) (D4) (C5) l. 000 0. 000 l. 000 0. 000 l. O00 .956 500 .707 856 259 865 .865 0. U00 .866 866 707 l. 000 707 0. C00 707 500 .866 -1. 000 866 .500

The scanning corner array antenna constructed in accordance with the foregoing design antenna is shown in conjunction with its associated beam steering means in FIG 9. The antenna is supplied with plane 73 for convenience in mounting the feed elements. @f the total of nine feed elements used, dipoles 37, d@ and 39 generate the cosine terms and dipoles through i5 generate the sine terms. The sine-generating elements are connected by cables 5:3', 55, 57 and SS of one half wavelength so that alternate elements are l out of phase. Power dividers 67 through 70, attenuators E@ through 6?., and trombone phase Shifters d3 through @d are used to provide control over the iive inputs. Each element or set of elements used to produce a particular term in the radiation pattern is preset by comparing its amplitude and phase with that of the cos 30 element. The signal at each set of terminals is set at the Value shown in the accompanying table for the prescribed angle, and patterns are taken without adiusting parameters for minimum beamwidth or low sidelobes.

A perspective veiw of this particular embodiment of my invention is illustrated by Flr?. l0 wherein reflecting surfaces 35 and 36 are shown mounted at a 60 angle on mounting structure 75. There is also shown dipole feed elements ffl-l5 and cables It is to be noted that the associated beam steering means of FIG. 9 is not included with FlG. l0 as only the perspective structure or" the corner antenna array is being illustrated.

There has thus been disclosed a practical scanning corner reflector antenna having high gain and a high degree of directivity wherein the several objects of my invention are accomplished. Although the particular embodiment disclosed illustrates a sixty degree, nine feed element device, it is not intended that the principles of my invention as taught herein be restricted thereto. It will be apparent to those having ordinary skill in the art that application of the principles of my invention will provide, within practical limits, scanning corner reflector antennae having any degree of gain feed elements, or any size corner angle.

surfaces being positioned on mounting means located at the vertex of the angle formed thereby, a plurality of feed elements disposed in parallelism with said vertex, and with each other, in a series of planes diverging from and including said vertex as a common access of intersection of all said planes, all of said parallel feed elements being located at discrete points along said several diverging planes and means for varying the currents applied to each of said feed elements. i 2. A corner reflector antenna in combination with a plurality of dipole feed elements, said dipole feed elements being disposed within said corner in parallelism along a series of planes having a common access of intersection at said comer, and being adapted to divert the beam produced thereby in response to the several currents applied to each of Said feed elements.

3. An electromagnetic Wave radiating device comprising a corner angle reflector, a rst series of feed elements disposed on the bisector of said corner angle, a second series of feed elements disposed on the sub-bisectors of said corner angle all of said sub-bisectors having a com- .mon access of intersection at the vertex of said corner angle, and means for varying the phase and magnitude of the currents applied to the several elements of said first and second series of feed elements.

`4. An electromagnetic Wave radiating device in accordance with claim 3 wherein said corner angle reector comprises two vertical intersecting plane surfaces of highly conductive material, and reflector mounting means.

5. An electromagnetic wave radiating device in accordance with claim 3 wherein the individual elements of said first and said second series of feed elements are disposed n acaso? i at discrete distances from the apex of said corner angle such that the Bessel function associated with the held `components produced thereby is substantially a maximum.

6. An electromagnetic wave radiating device in accordance with claim 3 wherein said means for varying the phase and magnitude of the currents applied to said feed elements comprises a plurality of power dividers, said power dividers being adapted to provide a separate input current for each of the several feed elements, a plurality of phase shifting devices, means for controlling said phase shifting devices in accordance with the desired radiation pattern and a plurality of attenuating elements, said attenuating elements being adapted to control the magnitude of the current applied to each of said feed elements.

'7. An ultra high frequency antenna comprising a corner angle reflector, said corner angle reflector consisting of two vertically intersecting plane surfaces of highly conductive material, a first series of feed elements, said first series of feed elements bein" adapted to provide cosine components of the eld pattern radiated thereby, a second series of feed elements, said second series of feed elements being adapted to provide sine components of the field pattern radiated thereby, all of said feed elements being located in planes having a common access of intersection at the vertex of said corner angle, and means for controlling the phase and magnitude of the several currents applied to said first and said second series of feed elements.

S. A corner angle reflector antenna comprising two intersecting plane surfaces of highly conductive material, a plurality of cosine producing feed elements, said cosine producing feed elements being disposed at discrete points on the bisector of the angle formed by the intersection of said plane surfaces, a plurality of oppositely phased pairs of sine producing feed elements,` the individual ele- Aments of each of said pairs being disposed at discrete points on the sub-bisectors of said angle formed by the intersection of said plane surfaces one on either side of said bisector, the intersection of said plane surfaces being coincident with the vertex of said corner angle, and means for varying the individual currents applied to said sine and said cosine producing feed elements.

References Cited by the Examiner UNlTED STATES PATEIJTS 2,523,895 9/50 Bailey 343-815 2,897,459 7/59 Stark 343-854 X 2,969,542 l/6l Coleman et al. 343-895 FOREIGN PATENTS 1,021,643 12/52 France.

HERMAN KARL SAALBACH, Primary Examiner.

Claims (1)

1. A SCANNING ANTENNA COMPRISING TWO INTERSECTING PLANE SURFACES OF HIGHLY CONDUCTIVE MATERIAL, SAID PLANE SURFACES BEING POSITIONED ON MOUNTING MEANS LOCATED AT THE VERTEX OF THE ANGLE FORMED THEREBY, A PLURALITY OF FEED ELEMENTS DISPOSED IN PARALLELISM WITH SAID VERTEX, AND WITH EACH OTHER, IN A SERIES OF PLANES DIVERGING FROM AND INCLUDING SAID VERTEX AS A COMMON ACCESS OF INTERSECTION OF ALL SAID PLANES, ALL OF SAID PARALLEL FEED ELEMENTS BEING LOCATED AT DISCRETE POINTS ALONG SAID SEVERAL DIVERGING PLANES AND MEANS FOR VARYING THE CURRENTS APPLIED TO EACH OF SAID FEED ELEMENTS.

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