US2556046A - Directional antenna system - Google Patents

Description

Patented June 5, 1951 UNITED isTATEs PATENT OFFICE 2556,046 DIREoi'ioNAi. ANTE'NNA SYSTEM Oscar T. Simpson, Philadelphia, Pa., assignor, by

mesne assinment's, tolfhilco Corporation, Philadelphia, Pal., a corporation of Pennsylvania Application March 28, 1948, serial No. 657,691

This invention relates to directional antenna systems adapted to radiate or receive ultra high frequency electromagnetic wave energy. More particularly, this invention has to do With novel means for improving and controlling the directional properties of directive antenna systems.

In consequence of the small physical dimen- .Sions of antennas and antenna systems available for use at ultra high frequencies, directional Wave propagaton is preferably accomplished through the use of simple antenna structures, such as horn radiators and refiector type antennas rather than by means of the more complicated and more critical antenna arrays usually employed at the lower radio frequencies.

The manner in which horn radiators and reflector type antennas function as a means of propagating electromagnetic wave energy in a desired direction is considered to be suificiently understoodl by those skilled in the art that only reference to some of the physical considerations of such antenna systems will be given here.

Highly directional radiation patterns may be obtained with simple horn radiators if the mouth or aperture is made large compared to the wavelength. Likewise, in a dipole and refiector type antenna system the width of the radiation pattem or beam becomes less as the diameter of the reflector mouth or aperture is increased. Thus for a given beam width, at a given frequency, these basic antenna structures must ne'cessarily have certain minimum dimensions.

.In many fiXed-service applications the dimen'- sions of the antenna system are not likely to be a significant factor. I-Iowever. in portable systems, and particularly in air-borne installations, it is important that the antennais physical dimensions, size, and weight be kept as small as' possible. Frequently it is equally important that the antenna may be constructed to have sufii-4 cient rigidity to withstand rough handling and vibraton in order that the electrical constants o f the system, and hence the radiation pattern, will not be subject to Variation.

The shape of the radiation pattern of a directive antenna system is primarily determined by the configuration of the wave front merging from the system. Thus a wave front having a high degree of curvature will give a comparatively wide beam, While a wave front of smallei' 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.

N ow I have found that by placing a phase' mod* ifyi'ng body in front of and along the axls ofa horn radiator I am able to s'ubstantia'llfy modify the radiataion pattern of the' 'propagatd energy. This phase-modifying body is preferably in the form of a metallic disc. With a disc of a certain siz'e placed at a certain distance in front of the' horn I am able greatly to increase the directivit'y of the mcdified horn over that of the horn alone. By means of the aforementioned arangement of a horn and a phase-modifying disc I am able to obtain a radiation pattern having a sp'e'cfi'd beam width With an antenna system which smalle'r and lightr than a conventio'nal horn capable of providing the same beam width;

'It is to be understood that my invention is not limited to the use of a horn radiator in om bination with a single phase-modifying body; II may employ in place of the horn other known devices for obtaining directional propagation of ultra high frequency energy, such as a dipole in combination with a spherical 'renector orH the like, and l may also use aplurality of phase modifying bodies of various configurations placed in various positions in front of the propagating device for the purpose of modifying or controlling the diree'tivity of the antenna system. i v

Thus, according to my invention,` VI proyidea novel means for altering the normalradi` pattern of a wave directing device by modifying the wave front of the energy issuing from the de'- vice. By modifying the wave front of the energy after it leaves the propagating device, I provide a directive antenna system that is more fiexible, more readily adjusted, less limited in its adjus't: ment, and capable of producing a greater variety of radiation pattern than known prior antenna systems. i

It is therefore an object of the present inven-`` tion to provide novel means for controlling the' directional characteristics of ultra high' frequency antenna systems.

Another object of this inventio'n is t improve the directional characteristicshof ultra high frequency antenna systems employing wave' directive striic'tures without increasing the physical dirriensions of the wave directive' structure.

Another object of the present invention' isto provide novel means for obtaining specialradiaftion patterns from ultra high frequency directive antenna systems.

Other objects and features of theppr'eent invention will become apparent from the following description taken' in conjunction with the ao' companying drawings in which: p

Fig's. IA and 1B are, respectively, side and'-` front elevation views illustrating one embodiment of the invention adapted to a horn radiator;

Figs. 2A and 2B are similar views illustrating another embodiment of the invention; and

Fig. 3 is a cross-sectional view of an alternative embodiment employing a biconical horn type of radiator.

Referring to the drawings, the horn radiator 4 together with wave guide 5 represents one forme of a conventional horn antenna system. The wave guide 5 may be excited in any well known manner, s-uch as by means of a capacity probe 6 extending into the guide from a coaxial cable input connection 1. Proper impedance match between the antenna system and a coaxial feeder cable attach-ed to connection 'i may be obtained by any one of the usual matching methods. For example, the non-radiating end of the waveguide 5 may be closed by a conducting end-plate preferably movable within the guide, and positioned at thecorrect distance from input connection i to give the desired impedance match. Since the above-mentioned elements comprise a well known arrangement of a horn antenna system a detailed description thereof is deemed unnecessary.

` At a given frequency a horn antenna has, of course, a radiation pattern of a certain gain and directivity depending upon the length of the horn, the horn flare angle, and the size of the mouth or aperture of the horn. With one of these factors fixed one or both of the others will have an Optimum Value for maximum directivity and gain.

To illustrate one manner in which the radiation pattern of a horn antenna may be modified in accordance with the principles herein set forth reference may be had to Figs. 1A and 1B. The arrangement shown may be employed to improve the directivity of the horn. To this end a metallic disc 9, acting as a director, is mounted in front of the horn, perpendicularly to and coaxially with the axis of the horn antenna system 4, 5. Any convenient and appropriate means may be employed to support the disc. By way of example, the phase-modifying disc 9 may be centrally apertured, as indicated at 9a, to engage dielectric supporting rod Ill which, in turn, is fixed to a dielectric' plate i i at the center thereof. As shown best in Fig. 1A, the plate i! may conveniently be supported by means of an annular flange |2 formed around the aperture of horn 4. If desired the metal disc may be slidably mounted on rod iii so that its axial position may be adjusted to produce a desired radiation pattern. The die1ectric elements I O and I should be composed of a substance or substances (e. g. a plastic or a ceramic) having low electrical losses, i. e., low power factor, at the opearting frequency. Polystyrene is an example of a suitable low loss plastic dielectric material. The determination of the size and position of disc 9 is more or less a cut and try" matter, with the size of the disc following the general rule that the phase-modifying body is preferably resonant at a slightly higher frequency than the energy being radiated.

In practicing this invention according to the Iembodiment shown in Figs. 1A and 1B, for the purpose of improving the directional properties of horn radiator 4, a 90 horn with Optimum length and aperture was excited in the TEu mode at a frequency of 2550 megacycles. The mouth of the horn was six and three-quarter inches in diameter and the distance from the mouth to the throat was one and three-quarter inches.

The diameter of wave guide 5 was three and onequarter inches. Dielectric supporting elements, rod IO and plate Il, consisted of a one-half inch diameter rod and a one-quarter inch sheet respectively of polystyrene. Several metallic director discs of various diameters were tested and it was found that to obtain maximum directivity with a given disc the distance of the disc from the horn was critical and a function of the disc diameter. Maximum directivity was obtained with a disc measuring just under a half-wavelength (21A inches) in diameter, and placed at a distance of approximately one-quarter wavelength (one and one-quarter inches) in front of the horn. With this particular arrangement the radiation pattern measured 30 in the horizontal plane and 34 in the Vertical plane. The radiation pattern of the horn alone measured 43 in the horizontal plane and 46 in the Vertical plane. The beam width in degrees as given above is with respect to the half power points.

As previously mentioned, this invention is not limited to the use of a single phase-modifying body; instead a pl'urality of such bodies, of various configurations, may be employed for the purpose of improving the directive properties of the antenna system or to obtain special radiation patterns. To illustrate such an embodiment of the invention, there is shown in Figs. 2A and 2B, by way of example, five phase-modifying metallic discs, 19, 20, 21, 22 and 23, all placed in front of horn 4. Preferably these elements are spaced from the mouth of Vthe hornfiloy a distance not greater than the diameter of the horn. The discs may be supported in any convenient manner. In the drawing a circular dielectric plate il, seated in the horn's annular fiange i2, supports a centrally positioned dielectric rod 25. Another ,circular dielectric plate 2G is centrally apertured to engage the supporting rod 25. Plate 25 carries themetallic phase-modifying discs E9, 20, 2|, and 22. The rod 25 is extended beyond the plane of plate 26 to carry a centrally positioned phasemodifying disc 23. The plate 26 and disc 23 may, of course, be arranged to be adjustably positioned on rod 25. It is evident that methods other than that shown in Fig. 2 for mountng the several phase modifying elements may be employed. For example, each of the discs lg to 22 may be mounted on separate rods projecting from plate I l to permit individual Variation of the distance of each element from the mouth of the horn for the purpose of obtaining still greater fiexibility and additional special pattern shapes. Although the phase-modifying bodies are illustrated as circular plates or discs, it is to be understood that talternatively they may be rectangular or ellipical.

Reference may now be had to the embodiment illustrated in Fig. 3 in which the present invention is applied to a directive radiator of the biconical horn type. The biconical horn is comprised of an upper conical member 30 and a centrally-apertured, lower conical member 3|. The foregoing elements, shown in section, are rotationally symmetrical about the Vertical axis X-X. The biconical horn may be driven in any known manner-for example by means of a coaxial line 32, the inner conductor 33 of which terminates in the apex 34 of the upper conical member 30.

In accordance with the present invention, Aa

phase modifying body 3'5, having the form of anv j -annular ring, is medially positioned between the conical members 3B and 3|. Preferably the diameter of the annular ring 35 is such as to place it Well beyond the mouth of the horn. For maximum directivity in a Vertical plane a spacing of approximtaely a quarter wavelength is suggested.

In the interests of clarity no means for supporting the ring 95 are shown; suitable supporting and spacing structures can, of course, be readily adapted from those illustrated in Figs. 1A and 1B.

The principles underlying the present invention have not yet been fully determined. It appears, however, that the phase-modifying discs (or the phase-modifying annular ring of Fig. 3) function as wave-refracting bodies which alter the phase of portions of the electromagnetic wave energy with respect to the phase of other portions thereof, and thus modify the radiation pattern of the antenna system. With specific reference to the embodiment of Figs. 1A and 1B, for example, it appears that the disc 9 tends to retard the phase of the wave passing therethrough, or in the vicinity thereof, in such 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 radiator to a more nearly plane wave front.

It will be apparent to those skilled in the art that the structures herein described may be utilized in either the reception or transmission of Wave energy, it being well understood that the characteristics of an antenna used to abstract energy from a passing wave are similar, in practically all respects, to those of the same structure used as a radiator.

Although this invention has been illustrated and described With reference to certain specific physical embodiments it is to be understood that the invention is not limited to such embodiments and that other apparatus and arrangements may be utilized within the scope of the invention as defined in the appended claims.

the plane of said mouth a distance of substan- 3. An ultra high frequency antenna system as claimed in claim 1, characterized in that the diameter of said disc is substanti-ally a half wavelength at the said Operating frequency.

An ultra high frequency antenna system comprising a horn radiator having a mouth through which electromagnetic wave energy may pass in a direction generally normal to the plane of said month, a dielectric plate seated in the mouth of said horn, a dielectrio rod centrally fixed to said plate and extcnding perpendicularly therefrom, and a phase-modifying wave-refraotive disc supported by said rod, said disc being Wholly outside of and spaced from said horn in a position coaxial With the axis of said horn, for altering the phase of a portion of said Wave energy with respect to other portions thereof, whereby to modify the radiation pattern of said horn.

5. An ultra high frequency antenna system as claimed in clairn 4, characterized in that said phase-modifying disc is electrically resonant at a frequency somewhat above the Operating frequency of said system.

6. An. ultra high frequency antenna system comprising a biconical horn radiator, said radiator being comprised of a pair of conical elements and having a month through which electromagnetic wave energy may pass, and a phasemodifying annular ring medially positoned between said conical elements, said annular ring being wholly outside of and spaced from said biconical horn, the diameter of said annular ring being greater than the rim-diameter of said biconical horn by substantially a half waveiength at the Operating frequency.

OSCAR T. SIMPSON.

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 2,370,053 Lindenblad Oct. 20, 1945 2,405,992 Bruce Aug. 20, 1946 2,415,089 Feldman Feb. 4, 1947 2,419,556 Feldman Apr. 29, 1947 2,429,601 Biskeborn et al. Oct. 28, 1947 2,442,951 Iams June 8, 1948 2,478,241 Chu Aug. 9, 1949 2.486,589 Chu Nov. 1, 1949 FOREIGN PATENTS Number Country Date 678,010 Germany June 24, 1939 694,523 Germany Aug. 2, 1940 OTHER. REFERENCES Electronics, March 1, 1946, page 101.

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