US2588610A - Directional antenna system - Google Patents

Description

1952 w. P. BOOTHROYD El AL 2,588,510

DIRECTIONAL ANTENNA-SYSTEM Filed June 7, 1946 BY mu 5. M

fiGE/Yf Patented Mar. 11, 1952 DIRECTIONAL ANTENNA SYSTEM Wilson P. Boothroyd and Harry F; Hartley, Jr., I Philadelphia, Pa., assignors to Philco Corporation, Philadelphia, Pa., a corporation of-Pennsylvania Application June 7, 1946, Serial No. 674,951

I 11 Claims. 1

This invention relates to directional antenna systems adapted to radiate or receive ultrahigh-:-

frequency electromagnetic wave energy. More particularly, the invention has to do with novelmeansfor improving and/r modifying the directional properties of wave directive structures.

In consequence of the small physical dimensions of antennas and antenna systems available for use at ultrahighfrequencies, directional propagation is preferably accomplished through the use of simple antenna structures, such ashorn radiators and reflector type antennas, rather than by means of the more complicated and more'critical arrays employed at-the lower radio frequencies.

The manner in which'horn-radiators andreflector type antennas function as a means for propagating electromagnetic wave energy in a desired direction is considered to be sufiiciently understood by those skilled in the art'that only a brief reference to some of the physical considerations of such antenna systems will be givenhere.

The shape of theradiation pattern of a directive antenna system is primarily determined by the configuration of the wave front emerging from the system. Thus a wave front having a high degree of 'curvaturewill give-a com paratively wide. beam, while a wave front having a smaller curvature will produce -a-narrower beam. In horn radiators it has been found that the energy: issuing from the mouth has a spherical wave front.

Highly directional radiation patterns; may :be 1

obtained with simple horn radiators-if the mouth or aperture is made large compared to the wavelength. Likewise, in a dipole and reflector type antenna system the width of the radiation pattern or beam becomes less as the diameter of the reflector mouth or aperture is increased; In practice, in order to obtainrelatively narrow beam widthswith these basic antenna structures, it has been necessary to employ large. structures having apertures of in-- conveniently large diameter.

In a copending application of Oscar T. Simpson; Serial No. 657,691, filed March 28, 1946, Patent No.'2,556,046 granted June 5, 1951, and

assigned to Philco Products Incorporated, there a is described an antenna system utilizing phase modifying wave refracting means mountedwholly outside of and spaced from a wave directive structure for the purpose of modifying thewave front of the energy. emerging. from the structure; 2 Such -an antenna system=-may be arranged to give increased directivity over that.

obtainable from-the wave structure alone, thereby permitting 'the use ofa smaller wave directive structure than normally would be required to give a radiation pattern of specified beam width."

The present invention is directed toward an" antenna system of the character described in", the aforementioned copendingapplication and' is characterized by certain novel improvements" .in the phase modifying means whereby further control of-the directional characteristics of such antenna systems is provided.

The improved antenna systems of the present invention may beused in conjunction with radar gun ranging equipment adapted for installation on aircraft. In aircraft installations it is particularly important that the antennas physicaldimensions and weight be kept as. small as possible, andthat the'antenna have sufficient rigidity to-withstand rough-handling and vibration. without-variation in its electrical: constants and 1 hence in its radiation patternf It is therefore a general object of this inventionto providea novel meansfor. controlling or modifying the directional characteristics of ultrahigh-frequency antenna systems.

Another object of this invention --is to provide, novel meansforobtaining special radiationpatterns from-ultrahigh-frequency directive anvtenna systems.

A- further" object ofthe presentinvention is. to provide an-ultrahigh-frequency directional antenna system which is smaller, simpler and less 1 costly to manufacture than previously known antenna systemsof like directivity,

A more specific object of the present invention is to provide an antenna system forgun ranging-equipment mounted on aircraft which,

for the. required beam width, -is lighter, more compact, lesscostly to manufacture, and less, subject to variation in its electrical characteristics when subjected to'vibration than previously known antenna systems.

Other objects-and advantagesof the presentinvention will become .apparent fromth'e follow ing-description taken-inconjunction with the accompanying drawings in which:

Figs. land 2 are, respectively,-side and front elevation views illustratingone embodiment of the invention; and

Figs. 3 and 4 are similar views illustrating another embodiment of. the invention.

The drawings-illustrate two specific antenna systems adapted for general use: or; withradar. gun 'rangin ...,mstallations onaircraft. Eachthe antenna system and a coaxial feeder cable attached to connection 1 may be obtained by any one of the usual matching methods. For example, the non-radiating end of the wave guide may be closed by a conducting end plate 8, preferably movable within the guide, and positioned at the correct distance from the input connection 1 to give the desired impedance match. It will be understood, of course, that the position and extent of insertion of the probe 6 also affects impedance match. Since the above-mentioned elements, per se, are well known a detailed description thereof is deemed unnecessary.

In the embodiment of the invention illustrated in Figs. 1 and 2, five spaced wave-refracting elements are mounted in front of horn along the principal axis of wave propagation thereof.

Each wave refracting element comprises a dielectric disc 9 and may include, in addition, a preferably adjacent, and smaller, metallic disc l0. Preferably the wave refracting elements are spaced at approximately half wavelength intervals starting from the mouth of the horn. Any convenient and aprropriate means may be employed to support the discs 9 and It]. By way of example, each disc may be centrally apertured, as indicated at I2, to engage dielectric supporting rod l3 which, in turn, is fixed to a dielectric plate [4 at the center thereof, As shown best in Fig. 1, the plate I4 is conveniently supported by means of an annular flange l5 formed around the aperture of horn 4. If desired the discs 9 and I0 may be slidably mounted on rod i3 so that their axial positions may be adjusted to produce a desired radiation pattern.

The dielectric elements 9, l3 and I 4 should be composed of a substance or substances (e. g. a plastic or a ceramic) having low dielectric losses,

i. e. low power factor, at the operating frequency.

Polystyrene is an examrle of a suitable low loss plastic dielectric material. For mechanical protection the wave-refracting elements 9-l0 may be'enclosed in a tubular cover of suitable dielectric material, e. g. Lucite or the like (see Figs. 3 and 4).

A physical embodiment of the structure illustrated in Figs. 1 and 2 was constructed for operation at a frequency of 2550 megacycles. The wave guide 5, which was approximately 1.5 inches long and excited in the TEOl mode, drove a horn radiator having a flare angle of about 90 degrees and a comparatively small aperture measuring about 3.5 inches in diameter, 1. e. approximately three-quarters of a wave length. Discs 9 were composed of polystyrene 0.25 inch in thickness and of the same diameter as the horn. The metal discs [0 were one thirty-second inch thick and about one and one-eighth inch, or one-quarter wave length, in diameter. The wave refracting elements 9-H) were spaced at half-Wave intervals along the support rod [3.

The above described antenna system produced a radiation pattern which was essentially afigure of revolution and which had a beam width pf 28 degrees at the half-power points. The only perceptible side lobe was a three-percent peak '70 degrees from the axis of revolution. Satisfactory operation of the system, including both impedance match and radiation pattern, was obtained over a band width of more than me.

To obtain the proper phasing of the wave energy required for destructive wave interference in planes transverse to the axis of the system it appears essential that the spacing between the pairs of elements closely approximate a multiple of a quarter wave length. Preferably the dielectric discs 9 should have a thickness of at least one-eighth inch, but the thickness within reasonable limits has been found to be not at all critical. Discs of larger diameter produce a narrower beam, and vice versa. By tapering the disc diameters so that the diameter of the last disc was half that of the first, the beam width for a five-element array was increased approximately two degrees. Increasing the diameter of the metal discs I0 produced a sharper beam but also increased the strength of the side lobes and caused a greater impedance mismatch between the horn and free space While some of the effects produced upon the radiation pattern by varying the diameters of the polystyrene and metal discs are mentioned above, it was found that within reasonable limits the dimensions of the discs were not critical, the shape of the radiation pattern being controlled primarily by the number of wave-refracting elements 9IB. Thus, in one experimental model, the horn alone produced a beam having a width of 60 degrees; the horn with three wave-refracting elements provided a beam having a width of 45 degrees; and the horn with seven waverefractive elements provided a 22-degree beam. However, with arrangements employing more than five elements additional side lobes began to appear. For instance, with the seven pair array, a 25 percent lobe appeared 30 degrees from the axis while a 5 percent lobe appeared at the 10 degree points. As mentioned above, the lobe characteristic is also a function of the metal disc diameter.

The novel wave-refracting array of the present invention is not, of course, limited to use in combination with primary radiators of the horn type, it being apparent, as pointed out in the abovementioned copending application, that other radiators (e. g. a dipole with spherical reflector) may be employed.

Instead of the pairs of dielectric and metallic discs shown in Figs. 1 and 2, other forms of wave refracting elements and other arrangements thereof may be employed to control the shape of the radiation pattern. A useful modification of the Wave refracting array is illustrated in Figs. 3 and 4, in which Fig. 3 is a side elevation with a portion of a housing member broken away to facilitate illustration, and Fig. 4 is an'end elevational view of the device shown in Fig. 3. This particular embodiment employs eight wave-refracting elements bearing reference numerals [9 to 26, mounted in front of horn 4, perpendicularly to and coaxially with the axis of the horn. The wave refracting elements, or discs, are composed of a suitable low-loss dielectric material, such as polystyrene. They may be supported in the manner previously explained in connection with the description of Figs. 1 and 2. The horn mouth or aperture, as well as the dielectric discs, measure about three-quarters of a wavelength in diameter. The first disc [9 is approximately one Wave length thick with its center at a distance of about three-quarters of a wave length from the mouth of the horn. Discs 20 to 25 are approximately'two-tenths-of a wave length thiclra Thecenter pf' disc!!! is about three-quarterswot:

a wave length-from-the center of diSC IQP-WhiIGe-lthe spacing between discs to -2 5 is approx-r is about a "half wave length thick with its cent-1 ter 1 approximately six-tenths of a wave-' lengthri from ---the --center of disc In the-= dimensions .1

given abovethe disc thicknesses are in ter ns of.-

wave length irrthe dielectricandthespacingsbea tweenelements are in: terms of free space wave length; Within limits the-various-discsthickan nesses are not critical; the beamlwidthibeingrpri-v.

marily an inverse function of the=number=cf .ele;- ments-used.

The entire --disc assembly;:may;..:be :enclosed::in.-1: a protectivecover 21 composedl of:-a mechanically and electrically suitable dielectrica terial. Lucite has been used successfullyforv this-wpurposel For mechanical. convenience in mounting thecoverthe discs maybe of thesam'e diameter as the horn. The .presenceof thecover. tendsto narrow the beam width.:

A physical embodiment of .the structure illus.- tratedin Figs. 3 and 4 wasconstructed. foruop erationata frequency. of .3285. megacycles. The horn-4 had a flare angle-of 100"degrees and,:a mouth measuring two and: three-quarter inches in diameter, disc 19 was one and seven-sixteenths inches thick, -.disc- .26 was -five-eighths -of an inch thick, and. discs 20 to 25 were each one-. quarter-of an, inch thick." All of. the discs, as wellv as 'rod' l3 and. plate I4 were .polystyrene.;. Cover 21 .was made ..from a piece-of: one-eighth inch thick Lucite.

The radiation patternof the. above-described antenna system hadla'beamzwidth of twenty-six degrees between half power points, with three percent side lobes at forty-five degrees from the axis of 11118-110111 Although thefrequencycfthe ap: plied energy was varied over a hundred megacycle band the beam.width varied but. one degree, the side lobes increasing to a maximum of four percent at the ends of the band. Exceptionallygood impedance match was- -maintained:- throughout this band, thestandingwave rati0,w lookinginto :the antenna from the transmitter, being less than -1 .2 over theband. V

The antenna system illustrated in Figs;---3 and" 4, may employ other driving or radiating :means similar to'those mentionedwith reference-to the system shown in Figs. 1 and'2.= Various -modifications-may also be madeinthenumber dia ameter, and-thickness of the discs- 9 to 26 in order to produce radiation patterns of other con-o figurations.

The principles underlying the present invention have not yet been fully determined. It appears however that the phase modifying ele ments, which may be termed director discs or phase retarders, function as Wave refracting bodies which alter the phase of portions of the electromagnetic wave energy with respect to other portions thereof and thus modify the radiation pattern. With specific reference to the embodiment of Figs. 3 and 4, for example, it appears that the discs l9 to 26 tend to retard the phase of the wave passing therethrough, or in the vicinity thereof, in such a manner as to more favorably phase the central portion of the radiated energy with respect to the outer portions thereof, and thus to convert the spherical wave front of the conventional horn to a more nearly plane wave front. The embodiment of the invention according to Figs. 1 and 2 may be con-' sidered toiwoperate .insa .:similar .-manner,-. .Withiith metal and polystyrene:- discs acting-to diiferentr-i;

degrees-,- uponrthe -wave. front,-::1the -:metal; disu e-z; being :more drastically efi'ective sthan theapolye 1 imately a quarter Wave-length.- The-lastdisc 26" 5 styrene discs in-=retardingthephase of; thegwaxre-t It will '-be'=. apparent to those 1 skilled in 1 the .art

that the structures herein. described maybe. lutie'a.

lizedsiin .either. the reception-or.transmission of.;.:- wavezenergypit beingqwell understood ;that,:the. -10 ;characteristics of: ran. .antenna .yusedyto abstract energy .from .a passing .wave are similar,.in pracetically all respects, to. those of :the same structure 2-;

used -as:a radiator-.1:-

Although...this invention =has..;.been illustrated 15 and :described with reference ;to certainspecificz;

physical .embodiments, it is to; be understood thattheinvention.- is not limitedito' such embodies mentsxand -that other-apparatus. .aanda arrange,-.-;-

ments may be utilizedwithin'the;scopeof the in-.-.1.-

2 ,;vention:-as .deflned-:in-:the appended claims;

We. claim:

1. An -.ultrahighfrequency antenna system: comprising a hollow -wave-directive': structure having a principal axis, said structure terminat- 25 ingm: an open mouthg through which electro,-,.-

so the plane ,of each of said-plates being perpendicu,

lar to said axis, and-meansasupporting said plates; 1-;

in positions outside-of and spaced from-said,

structure, said plates being; arran ed coaxially with respect to' said structure:

ultrahighefrequency antenna: system; '1 comprising a conical; horn. :radiator terminating; in an; open mouth and having ag=principal :axis:

of wave propagation extendingI centrallythrough,

saidxmouth in a direction .normalqto the plane; 40 ,thereof, a dielectric ;rod, means supporting said, 1

rod ;onthe, line of said. axis and in a position,

extending; outwardly from said mouth,- andgay plurality of centrally-apertureddielectric, discs through the apertures of whichsaid rod extendsv whereby to; support. said discs: in planes parallel tothe plane of said mouth, said discs beingy mutually spaced along said rod in confronting relation with said mouth.

themouth ofsaid horn.

4.-;Anrultrahigh-frequency antenna system 4 as,

5; claimed in claim 2, characterized in .that 12116;:

thickness of, said discs is :substantially lessjthan the spacing therebetweem;

5.;qAn ultrahigh-frequency antenna system-.1 comprising a hollow wave-directivemstructure having a principal axis. said structure terminating in an open mouth through which electromagnetic wave energy may pass in the direction of said axis, and a plurality of dielectric plates each having parallel plane surfaces, the

lateral dimensions and area of said plates being substantially equal to the lateral dimensions and area of said mouth, said plates being mutually spaced along said axis and disposed outside of and spaced from said structure in positions opposite the mouth thereof, the plane of each of said plates being perpendicular to said axis. said plates being arranged coaxially with respect to said structure, said plates being effective to modify the radiation pattern of said structure. 1

6. An ultrahigh-frequency antenna system as claimed in claim 5, characterized in that the spacing of at least certain of said dielectric plates is substantially an integral multiple of a quarter wavelength at the operating frequency.

7. An ultrahigh-frequency antenna system comprising a horn radiator terminating in an open mouth and having a principal axis of wave propagation extending centrally through said mouth in a direction normal to the plane thereof, and a plurality of dielectric plates each having parallel plane surfaces, the lateral dimensions and area of said plates being substantially equal to the lateral dimensions and area of said mouth, said plates being mutually spaced along said axis and disposed outside of and spaced from said horn radiator in positions opposite the mouth thereof, the plane of each of said plates being perpendicular to said axis, said plates being arranged coaxially with respect to said radiator, and the spacing of at least certain of said plates being substantially an integral multiple of a quarter wavelength at the operating frequency.

8. An ultrahigh frequency antenna system comprising a horn radiator terminating in an open mouth and having a'principal'axis of wave propagation extending centrally through said mouth in a direction normal to the'plane thereof, and a plurality of dielectric plates mutually spaced along said axis and disposed outside of and spaced from said horn radiator in a position opposite the mouth thereof, the plane of each of said plates being perpendicular to said axis, said plates being arranged coaxially with respect to said radiator, at least certain of said dielectric plates having conjoined therewith conducting metal plates, the dimensions of said metal plates being less than the corresponding dimensions of said dielectric plates.

9. An ultrahigh-frequency antenna system comprising a horn radiator terminating in an open mouth and having a principal axis of wave propagation extending centrally through said mouth in a direction normal to the plane thereof, and a plurality of dielectric plates each having parallel plane surfaces, the lateral dimensions and area of said plates being substantially equal to the lateral dimensions and area of the mouth of said horn, said plates being mutually spaced along said axis and disposed outside of and spaced from said'horn radiator in positions opposite the mouth thereof, the plane of each of said plates being perpendicular to said axis, said plates being arranged coaxially with respect to said radiator, and .the spacing of at least certain of said plates being substantially an integral multiple of a quarter wavelength at the operating frequency.

10.'An; ultrahigh-frequency antenna system 7 0 positions opposite the mouth thereof, the spacing of at least certain of said dielectric plates being substantially an integral multiple of a quarter wavelength at the operating frequency, the plane of each of said plates being perpendicular to said axis, said plates being arranged coaxially with respect to said radiator, and the thickness of said plates, measured along said principal axis, being substantially less than the spacing between said plates.

11. An ultrahigh-frequency antenna system comprising a hollow wave-directive structure.

having a principal axis, said structure terminating in an open mouth through which electromagnetic Wave energy may pass in the direction of said axis, and a plurality of dielectric plates each having parallel plane surfaces, said plates being mutually spaced along said axis and disposed outside of and spaced from said structure in positions opposite the mouth thereof, the plane of each of said plates being perpendicular to said axis, said plates being arranged coaxially,

with respect to said structure, and substantially all of the area of each of said plates directly confronting the open mouth of said wave-directive structure.

WILSON P. BOOTHROYD. HARRY F. HARTLEY, JR.

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

UNITED STATES PATENTS

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