US2889552A - Antenna unit - Google Patents

Description

June 2, 1959 F. e. THOMAS ET AL ANTENNA UNIT Filed Aug. 31, 1956 2 S S T .C T GN N V M E mmm M L Y ANTENNA UNIT Frank G. Thomas, Bay Shore, and William M. Millar,

North Babylon, N.Y., assignors to International Tolephone and Telegraph Corporation, Nutley, N J., a corporation of Maryland Application August 31, 1956, Serial No. 607,337

16 Claims. (Cl. 343-761) This invention relates to antenna units and more particularly to broad-band antennas for operation at very high and/ or ultrahigh frequencies.

In many antenna systems, particularly those used in direction-finding systems, it is desirable that the antenna have a rotating directional pattern and be sensitive only to vertically polarized waves. It is well known that in order to design a wide band dipole antenna, it is necessary to make a diameter of the dipole a substantial fraction of the wave length of the frequency for which the antenna is designed. However, as the diameter of the dipole is increased, the antennas sensitivity to horizontal polarizations will increase. In some instances it is desirable to rotate the directional pattern of the vertical antenna, and this may be done by means of a rotating reflector. Horizontally polarized Waves, however, tend to induce voltages in antennas having reflectors whose width is a substantial fraction of the Wave length of the received radiation. Thus, antenna units having reflectors of this type will induce polarization errors'in the direcnon-finding systems.

In the U8. Patent No. 2,726,389,. granted to I. R. Taylor, entitled Antenna Unit, one solutiontothe above problemris disclosed. The Taylor patent employs a plurality of parasitic reflectors spaced about a cylinder of insulating material which is disposed concentric to a vertically disposed dipole. A directionalradiation pattern is provided by this arrangement and said pattern is rotated by rotation of the cylinder carrying the parasitic reflectors.

An object of this invention is to provide. a directional antenna unit which is an improvement over the antenna unit of the above identified Taylor patent.

Another object of this invention is to provide a directional antenna utilizing a reflector which is effectively rotated and is substantially insensitive to horizontally polarized waves.

Still another object of this invention is to provide a wide-band antenna having a rotating directional pattern capable of receivingsubstantially only vertically polarized radiations.

A ftu'ther object of' this invention is to provide a wideband antenna arrangement having a reflector which is effectively rotated to provide the desired rotating directional pattern.

According to a feature of this invention, a wide-band coaxial dipole antenna is provided. A plurality of parasitic elements are disposed concentrically about said dipole antenna. Each of theparasitic elements is broken or divided at one or two places along its length. A coupling unit is disposed adjacent each of the breaks in the parasitic elements to capacitively couple together the divided conductive portions of the parasitic elements. The coupling means is rotated about the dipole to establish a rotating directional antenna pattern. The length of the parasitic elements are such that with no coupling, each parasitic element acts as a director. As the rotating coupling disc capacitively couples the conductive nite States Patent portions of the aparasitic element together, the parasitic element then becomes a reflector. The metal mass on the rotating coupling disc can be formed so that any number of parasitic elements can be made as reflectors and the degree of capacitive coupling to the elements can be altered to obtain a particular antenna pattern.

In accordance with further features of this invention the capacitive coupling element may be made up of a plurality of conductive masses such that a multiple lobe radiation pattern is produced by the antenna, the lobes of the radiation patterns corresponding in number to the number of conductive masses on the coupling element. The natural resonant frequency of the parasitic elements may further be modified by coupling an inductance in series between the adjacent conductive masses of the coupling element.

The above-mentioned and other features and other features and objects of this invention will become more apparent by reference to the following description taken in conjunction with the accompanying drawings, in which:

Fig. 1 is a partial perspective view, with parts broken away, showing the antenna and parasitic element arrangement of this invention as coupled in a circuit for direction-finding purposes;

Figs. 2 and 2A illustrate details of the coupling element of Fig. 1; and

Figs. 3, 4, and 5 illustrate various radiation patterns available with the antenna system of this invention as the conductive masses are increased in number.

Referring to Fig. l, a preferred embodiment of the antenna unit of thisinvention is illustrated as including a vertically extending coaxial dipole antenna 1. A coaxial transmission line 2 has its inner conductor 3 coupled to the upper element 4 of dipole l and its outer conductor 5 coupled to the lower element 6 of dipole l. The dipole I may be supported in any Well known manner, one expedient being illustrated in the above-mentioned Taylor patent. Concentric and coaxial with dipole 1 is a cylinder 7 composed on an insulating material, such as a ceramic or fiberglass, which does not affect the radiation pattern of the antenna. A plurality of conductive strips 3, shown in Fig. 1 each divided into three conductive portions 9, 10 and 1]., are disposed either within the wall of cylinder '7 or on the surface thereof to function as parasitic elements. It is preferred that strips 8 be silver material fired on the surface of cylinder 7 at regular spaced intervals.

Although strips 8 are illustrated to have three conductive portions and two breaks or gaps therein, it is to be understood that strips 8 need only have one gap therein, that is, two conductive portions, or could have more than two gaps therein, to achieve the same end result, a rotating directional radiation pattern as is hereinbelow described.

Intermediate dipole 1 and cylinder 7 and concentric therewith is disposed a hollow shaft 12 of electrical insulating material having mounted thereon, in juxtaposition with gaps 15 and 16, discs 13 and 14- of insulating material. On the periphery of discs 13 and 14 are dis posed conductive masses 1'7 and 18, respectively, disposed relative to strips 8 to capacitively couple together the divided conductive portions 9, 10 and 11 of certain of the strips. A detailed illustration of the capacitive coupling element including mass 17 and disc 13 is shown in Fig. 2. The conductive masses 17 and 18 each have a plurality of functions. One function is to capactively couple together the divided portions of each of strips 8 as the mass reaches a position adjacent thereto. Another function is to capacitively couple a number of strips 8 together as the mass reaches a position adjacent thereto. Accordingly each mass preferably has a vertical height as great as or greater than the gap or 16 it is bridging, and preferably has an arcuate length equal to the number of strips which it is to couple together. To provide a smooth transition the ends of each mass are tapered. When the capacitive masses 17 and 18 are in capacitive coupling relation with certain of the strips 8, these parasitic elements have a length substantially equal to the length of dipole 1 which is sufficient to reflect the radiant energy in the operating frequency range of the antenna unit and thus the parasitic elements becomerefiectors. Those other parasitic elements which are not coupled together capacitively have a natural resonant frequency which renders them efiectively directors for the operating frequency of the antenna unit, the length being substantially shorter than the length of a dipole antenna. The

resultant radiation pattern will then be that radiation pa:

tern illustrated in Fig. 3. The sharpness or directivity of the lobe of the radiation pattern depends upon the total amount of periphery masses 17 and 18 occupy on discs 13 and 14. It has been found that 120 occupancy by masses 17 and 18 provide a relatively sharp direc tional lobe. If this occupancy by masses 17 and 18 is reduced, the lobe will become less sharp and if the occupancy is increased, the lobe will become sharper. The shaft 12, and hence the discs 13 and 14, is mechanically rotated by means of motor 19 which is directly coupled thereto. The shaft of motor 19 is hollow to enable the coaxial transmission line 2 to extend therethrough. The gear train and mechanical linkage permits the alternator 21 to be driven in synchronism with shaft 12. Body 22 is disposed on the surface of discs 13 and 14 to counterbalance the weight of masses 17 and 18 and thereby balance discs 13 and 14 for more easy rotation thereof by shaft 12.

As pointed out hereinabove, strips 8 may have one, two, or more breaks in the length thereof with the conductive portions adjacent each gap being capactively coupled by a rotating conductive mass to provide the desired rotating radiation pattern.

In order to have a response over a relatively wide frequency range, dipole 1 is a low-Q wide band coaxial dipole. A design of such a dipole antenna, in order to have a wide frequency response, requires a diameter which is relatively large when compared to the wavelength of the radiations for which it is designed, and because of this large diameter, the antenna 1 will be sensitive to horizontal polarization. The lower half 6 'of the dipole is coupled to the outer conductor 5 of a coaxial transmission line 2 and shields the transmission line thus preventing it from affecting the radiations received by the antenna unit. The length of the dipole is designed so that it is resonant at the median frequency of the frequency band for which it is to be used. The

conducting strips 8 each have an electrical length, when the conductive portions are capacitively coupled together, equal to one half the wavelength at the lower end of the frequency band of the low-Q dipole. The width of each conducting strip is made as narrow as possible consistent with the requirement that the strips provide adequate conduction. Thus, they may consist of a plurality of wires or ribbons of conductive material, they may be painted on cylinder 7 with a metallic or conductive paint, or they may be formed from a conductive material, such as silver, which is fired on cylinder 7. The parasitic elements, because of the narrow width of the strips are in sensitive to horizontal polarization but do reflect and direct vertically polarized waves, thus, in eifect, cancelling the tendency of the wide band dipole to be sensitive to horizontal polarizations. The spacing between strips is small enough to provide adequate reflection of the vertically polarized waves and wide enough to prevent excess capacitance between strips 8 which might change the electrical length of the strip or might present the equivalent of a solid reflected area and thus reflect horizontally polarized radiations.

An example of one form of antenna unit that could be used in accordance with this invention in a frequency band of 150 megacycles to 300 megacycles comprises a coaxial dipole 24 inches long and conductive strips having portions 9 and 11 each five inches long and portion 10, twenty inches long. Conductive strips 8 are naturally electrically resonant at 238 megacycles when functioning as directors, that is, when not in the region of capacitive coupling by masses 17 and 18. The masses 17 and 18 are one and a half inches wide occupying approximately on the periphery of discs 13 and 14. The gaps 15 and 16 of strips 8 are approximately one quarter of an inch. When portions 9 and 11 are capacitively coupled to portions 10 by masses 17 and 18 the parasitic elements, now behaving as reflectors had, in one embodiment, a natural resonant frequency of 187'megac'ycles.

The parasitic strips are silver material fired on a ceramic cylinder, each being 4 inch wide and spaced inch apart upon a radius of 8 inches. The spacing between dipole 1 and strips 8- are 8 inches. masses 17 and 18 can be reduced to approximately one half inch as any greater amount of coupling has little change in the natural resonant frequency.

The embodiment of this invention illustrated in Fig. 1 is shown connected in a circuit for direction finding purposes. In this arrangement the discs 13 and 14 are rotated by means of motor 19 which also drives alternator 21 in synchronism therewith. The alternator 21 feeds a reference voltage to the stator winding 23 of a phase meter 24. The antenna transmission line 2 is coupled to the rotor winding 25 of the phase meter 24 through a receiver and amplifier 26 and a high impedance 27. The azimuth of the received signal may be indicated by the rotation of rotor 25 of phase meter 24 in response to the phase relation of the received signal from the dipole antenna 1 and the reference voltage from the alternator former 27 between the amplifier 26 and the rotor wind- 7 ing 25 of the phase meter 24.

Hereinabove we have described an antenna unit to provide a directional radiation pattern as illustrated in Fig. 3. This has been accomplished by employing a single conductive mass occupying a given portion of periphery of the rotating discs 13 and 14. In Fig. 3 disc 13 is illustrated as carrying a conductive mass 17 on approximately 120 of its periphery. The antenna radiation pattern can be altered substantially as illustrated in Fig. 4 by dividing mass 17 into two separate messes as represented by masses 28 and 29 in Fig. 4. Masses 28 and 29 occupy approximately 30 on the periphery of disc 13 and are separated from each other by approximately 30 of the peripheral are. When this arrangement is employed, a two-lobed radiation pattern is obtained as illustrated. It should be pointed out herein that the amount of spacing between masses 28 and 29 and the peripheral area occupied by 28 and 29 may be varied to provide difierent shaped lobes than that illustrated in Fig. 4. r

Fig. 5 illustrates still another modification of massm 17 and 18 to provide still another radiation pattern. As illustrated, the'radiation pattern is a three-lobed afiair which is achieved by splitting mass 17 into three distinct masses 30, 31 and 32. These masses may occupy a given portion of the periphery of disc 13 and may be separated by a given amount along the peripheral arc of disc 13 to provide a desired shape for the lobes of the radiation pattern of the antenna system of this invention.

In Fig. 2A masses 30, 31 and 32 have coupled thereto in series inductances 33 and 34. This addition of inductances 33 and 34 aid the capacitive components, due to masses 3!), 31 and 32, in the tuning of the parasitic elements to a desired frequency when these parasitic elements are to function as a reflector.

The entire antenna unit may be enclosed for protection against the weather and other climatic conditions much as disclosed in the above-identified Taylor patent.

While we have described above the principles of our invention in connection with specific apparatus, it is to be clearly understood that this description is made only by way of example and not as a limitation to the scope of our invention as set forth in'the objects thereof and in the accompanying claims.

We claim: I,

1. 'An antenna system comprising antenna means having a vertically polarized characteristic vertically disposed, conducting strips disposed concentrically about said antenna means, each of said conducting strips being divided into at least two conducting portions, movable means disposed concentric of said antenna means for capacitively coupling the divided conducting portions of certain of said conducting strips to each other, and means to move said last-mentioned means.

2. An antenna system comprising antenna means having tions of certain of said conducting strips to each other and means to rotate said body to bring said conductive mass into capacitive coupling relation with others of said conducting strips.

3. An antenna system comprising antenna means having a vertically polarized characteristic vertically disposed, a cylinder of insulating material disposed concentrically about said antenna means, conducting strips carried by said cylinder, each of said conducting strips being divided into at least two conducting portions, a disc disposed intermediate said antenna means and said cylinder having a conductive mass disposed on a given portion of the periphery thereof for capacitively coupling the divided conducting portions of certain of said conducting strips to each other, and means to rotate said disc to bring said conductive mass into capacitive coupling relation with others of said conducting strips.

4. An antenna system comprising antenna means having a vertically polarized characteristic vertically disposed, a cylinder of insulating material disposed concentrically about said antenna means, conducting strips carried by said cylinder, each of said conducting strips being divided into at least two conducting portions to provide radiant energy directors, and a body disposed concentrically of said antenna means having a conductive mass for capacitively coupling the divided conducting portions of certain of said conducting strips to each other to provide radiant energy reflectors.

5. An antenna system comprising antenna means having a vertically polarized characteristic vertically disposed, a cylinder of insulating material disposed concentrically about said antenna means, conducting strips carried by said cylinder, each of said conducting strips being divided into at least two conducting portions, said divided conducting portions having an electrical length sufiicient to render said conducting strips elfectively radiant energy directors in the operating frequency of said antenna means, a body disposed concentrically of said antenna means having a conductive mass for capacitively coupling the divided conducting portions of certain of said conducting strips to each other, said coupled divided conducting portions thereby providing said certain of said conducting strips with an electrical length suflicient to 6 operate effectively as radiant energy reflectors in the operating frequency of said antenna means, and means to rotate said body to bring said conductive mass into successive capacitive coupling relation with others of said conducting strips to establish a rotating directional radiation pattern.

6. An antenna system comprising antenna means having a vertically polarized characteristic vertically disposed, a cylinder of insulating material disposed concentrically about said antenna means, conducting strips carried by said cylinder at regularly spaced intervals, each of said conducting strips being divided into at least two conducting portions, a disc of insulating material disposed intermediate said antenna means and said cylinder having a conductive mass disposed on a given portion of the periphery thereof for capacitively coupling the divided conducting portions of certain of said conducting strips to each other, and means to rotate said disc to bring said conductive mass into successive capacitive coupling relation with others of said conducting strips.

7. An antenna system comprising antenna means having a vertically polarized characteristic vertically disposed, a cylinder of insulating material disposed concentrically about said antenna means, conducting strips carried by said cylinder at regularly spaced intervals, each of said conducting strips being divided into at least two conducting portions, a shaft of insulating material disposed intermediate to and concentric with said antenna means and said cylinder, a disc of insulating material secured to said shaft at a point therealong to dispose said disc adjacent the gap between said divided conducting portions, said disc having a conductive mass disposed on a given portion of the periphery thereof for capacitively coupling the divided conducting portions of certain of said conduct ing strips to each other and means to rotate said shaft to bring said conductive mass into successive capacitive coupling relation with others of said conducting strips.

8. An antenna system comprising antenna means having a vertically polarized characteristic vertically disposed, a cylinder of insulating material disposed concentrically about said antenna means, conducting strips carried by said cylinder at regularly spaced intervals, each of said conducting strips being divided into at least two conducting portions, a disc of insulating material disposed intermediate said antenna means and said cylinder having a conductive mass disposed on a given portion of the periphery thereof for capacitively coupling the divided conducting portions of certain of said conducting strips to each other, said conductive mass being predeterminedly shaped to control the degree of capacitive coupling and the number of strips being coupled, and means to rotate said disc to bring said conductive mass into successive capacitive coupling relation with others of said conducting strips.

9. A system according to claim 8, wherein said conductive mass includes a continuous body of conductive material occupying a given peripheral arc of said disc.

10. A system according to claim 9, wherein said conductive mass includes a plurality of bodies of conductive material each occupying a given peripheral arc of said disc in a given spaced relation with respect to adjacent ones of said plurality of bodies of conductive material to provide a rotating radiation pattern having a plurality of lobes equal to the number of said bodies.

11. A system according to claim 10, wherein said plurality of bodies of conductive material number two.

12. A system according to claim 10, wherein said plurality of bodies of conductive material number three.

13. A system according to claim 10, wherein an inductance is disposed in series relationship with adjacent ones of said plurality of bodies of conductive material to aid in the tuning of said conductive strips when said conductive strips are in capacitive coupling relation with said plurality of bodies of conductive material.

14. An antenna system comprising antenna means having a vertically polarized characteristic vertically disposed,

a'cylinder of insulating material disposed concentrically "about said antenna means, conducting strips carried by portions therealong, corresponding non-conducting portions of each of said conducting strips being disposed on the same diameter of said cylinder, a plurality of discs of insulating material each having a conductive mass disposed on a given portion of the periphery thereof disposed intermediate said antenna means and said cylinder and adjacent each of said corresponding non-conducting portions of said conducting strips, said conductive masses capacitively bridging said corresponding non-conducting portions to thereby provide a continuous conducting strip and to couple certain one of these continuous conducting strips together, and means to rotate said discs in synchronism to bring said conductive masses into successive capacitive coupling relation with others of said conducting strips.

15. An antenna system comprising antenna means having a vertically polarized characteristic vertically disposed, a cylinder of insulating material disposed concentrically about said antenna means, conducting strips carried by said cylinder at regularly spaced intervals, each of said conducting strips having a plurality of non-conducting portions therealong, corresponding non-conducting portions of each of said conducting strips being disposed on the same diameter of said cylinder, a shaft of insulating material disposed intermediate to and concentric with said antenna means and said cylinder, a plurality of discs of insulating material secured to said shaft at a point therealong to dispose each of said discs adjacent one said corresponding non-conducting portion of said conducting strips, each of said discs having a conductive mass disposed on a given portion of the periphery thereof to capacitively bridge said corresponding non-conducting portions to thereby provide a continuous conducting strip andto couple certain ones of these continuous conducting strips together, and means to rotate said shaft to bring said conductive masses into successive capactive coupling relation with others of said conducting strips.

16. An antenna system comprising a coaxial dipole vertically disposed, a cylinder of insulating material disposed concentrically about said dipole, conducting strips carried by said cylinder at regularly spaced intervals, each of said conducting strips having tWo non-conducting portions therealong, one of said non-conducting portions being adjacent the upper end of said conducting strips and the other of said non-conducting portions being ad- 'jacent the lower end of said conducting strips, a shaft of insulating material disposed intermediate to and concen- V References Cited in the file of this patent UNITED STATES PATENTS Yagi May 24, 1932 Leeds Dec. 3, 1946

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