US3074064A - Self-supporting dipole antenna with balanced-to-unbalanced transformer - Google Patents

Description

Jan. 15, 1963 s. PICKLES 3,074,064

SELF-SUPPORTING DIPOLE ANTENNA WITH BALANCED-TO-UNBALANCED TRANSFORMER Filed Feb. 24. 1960 FIG? if 36 3; mmvroa flour/"7x455 I TTGINEY" Elite rates atent Ofiice 3,074,064 SEL -SUPPGRTENG DIPOLE ANTENNA BALANCED T6 UNBALANCED TRANS- FGRMER Sidney Pickles, Tonopah, Nev. Filed Feb. 24, 1960, Ser. No. 10,679 1 (Ilairn. (Cl. 343-897) The present invention relates to an improved antenna structure providing for the support and energization of antenna rathators without the utilization of electrical insulation.

It is often desirable in the design of antennas to provide for self-supporting means, and this is particularly true in the very high frequency and ultra-high frequency fields. The self-supporting of antennas poses certain problems in that the insulating supports are normally incapable of withstanding mechanical loads which may be applied to the antenna. This problem is intensified for those antenna applications wherein severe weather conditions, for example, are encountered by the antenna in use. Thus, the accumulation of ice, for example, upon self-supporting antennas has been found to be generally destructive of the support thereof. Attempts to overcome these difliculties by conventional approaches have led to the development of oversized insulating elements oftentimes including very costly materials, in order to maintain the dielectric losses at a reasonable level. It is common in self-supporting antenna structures for the necessarily massive insulating elements to introduce undesirable effects, such as excessive shunting capacities. The present invention is directed to the provision of fully metallic antenna structures, wherein all support members are formed of structurally strong metal elements so as to thereby entirely overcome prior-art difiiculties in the provision of suitable insulating mountings.

Of further importance in the design of antenna structures is the necessity of providing balanced voltages to balanced impedances. In those instances wherein only unbalanced voltages are available from the power source or generator, it is necessary to introduce some type of balanced-to-unbalanced transformer in the antenna connections. An example of this situation is found in the energization of dipole antennas, for it is well recognized that a dipole radiator, in order to function properly, must have voltages of equal amplitude and opposite phase applied to corresponding portions of the dipole parts. Stated otherwise, the currents flowing in the opposite halves of the dipole must be of substantially like amplitude and opposite phase in order for the radiation pattern of the dipole to approach theoretical values. Although it is common to employ coaxial cables in the feeding of radio frequency loads, such as antennas, it will be appreciated that the direct connection of an unbalanced voltage source to a dipole through a coaxial cable will produce an unbalanced voltage upon the dipole, so that undesirable radiation patterns therefrom are realized. This particular problem has received some consideration, and as a result there are known in the prior art certain balanced-to-unbalanced transformers adapted for utilization in the energization of dipole antennas from unbalanced voltage sources. The present invention provides a new and improved balanced-to-unbalanced transformer arrangement for the energization of radio frequency loads, such as dipole antennas, from an unbalanced voltage source, and combines this transformer structure with metallic support structure, as indicated above, to thereby provide a materially improved and simplified antenna structure.

It is an object of the present invention to provide an improved antenna structure providing a highly directional radiation pattern.

it is another object of the present invention to provide an improved antenna radiator support and combined energization means for maximum structural rigidity of the antenna.

It is a further object of the present invention to provide an improved antenna radiator support and energization means, combining fully metallic supports for maximized structural strength and balanced radiator energization for maximized directional radiation patterns.

Various other objects and advantages of the present invention will become apparent to those skilled in the art from the following description of particular preferred embodiments of the present invention; however, no limitation is intended by the terms of the following description, and, instead, reference is made to the appended claim for a precise delineation of the true scope of the present invention.

The invention hereof is illustrated in the accompanying drawings, wherein:

FIG. 1 is a cross-sectional view of a dipole antenna illustrating structural mounting features and energization connections in accordance with the present invention;

FIG. 2 is a partial sectional view of a dipole antenna illustrating alternate electrical connections for energization of the antenna in accordance with the present invention.

Considering the present invention in some detail, and referring to a simplified embodiment thereof illustrated in FIG. 1 of the drawings, there will be seen to be shown a pair of axially-alined hollow cylindrical antenna radiators 11 and 12. These antenna radiators may be quite conventional in form, and each have a length equal to one-quarter wavelength of the carrier frequency of energy to be radiated from the antenna. Extremely strong structural support for the radiating elements 11 and i2 is provided by a metallic support member 13, disposed axially through the radiating elements and secured to end caps 14 and 16 at the opposite ends of the elements. The mechanical connection of the support member 13 to the radiating elements is preferably made quite strong, and serves also as an electrical connection. A further portion of the supporting means of the antenna includes a mast or perpendicular branch 17, firmly aPdxed to the axial support member 13 and extending generally perpendicularly therefrom, intermediate the radiating elements 11 and 12. This mast 17 may have any desired length, and any suitable connection to means upon which the antenna is to be mounted. Thus, for example, the mast 17 may be mounted on an automobile, or the like, if desired, through the utilization of suitable metallic mounting means at the foot 'of the mast. With the foregoing support members securely afiixed to the radiating elements, it will be seen that the antenna is structurally solid, and that high structural strength is provided the mounting means.

As a further portion of the present invention, there is provided in combination with the metallic support means hereof, suitable connections for providing a balanced-tounbalanced transformation, whereby an unbalanced signal generator may be connected to the antenna. In this respect, it is noted that balanced energization of the radiating elements of a dipole antenna are required in order to attain highly directional radiation propagation characteristics from the antenna. By the energization of the two radiating elements with voltages of equal amplitude and opposite phase, it will be appreciated from general antenna theory, that the radiating pattern therefrom is highly directional with a maximumradiation intensity lying on the perpendicular bisector of the two radiating elements. Energization of the radiating elements is herein accomplished through the metallic support means for the radiating elements, and, as shown in FIG. 1, there may be connected an unbalanced signal source 18 through a coaxial cable 19 to the antenna. It is quite conventional to employ coaxial cables for the energization of high frequency antennas; however, it is Well recognized that a coaxial cable is an unbalanced system, so that some provision must be made for balancing the energizing voltages at the antenna, in order to obtain the desired radiation characteristics thereof. In the present instance, this is accomplished by extending the coaxial cable 19 through the support mast 17 and thence through one arm of the axial support member 13 to the end cap 16 of the radiator 12. The coaxial cable sheath 21 is electrically connected to the metallic support means of the present invention, while the central conductor 22 of the coaxial cable is insulated therefrom by the cable itself. At the outer end of the radiator 12, the coaxial cable 19 is extended through the end cap 16 and thence back to the inner end of this radiator 12. Although the coaxial cable is indicated as being disposed upon the exterior surface of the radiator 12, it may alternatively be provided interiorly of same; however, the coaxial cable extends to the inner end of the radiator 12. At this point, the coaxial cable is terminated with the sheath 21 thereof in electrical contact with the radiator, and the central conductor of the coaxial cable extending into connection with the adjacent end of the radiator 11. This connection is preferably made to the sheath 23 of a further coaxial cable 24, which extends the length of the second radiator ll. It will thus be seen that the voltage supplied by the generator 18 to the coaxial transmission line 19, is transmittcd through this line and is applied between the shields 21 and 23 of the two transmission lines 19 and 24. Inasmuch as the lengths of these shields back to a zero or reference voltage point are equal, it thus follows that equal portions of the applied voltage across the gap between the radiators 11 and 12 will operate to transmit waves of energy equally along both radiators. The continuous metallic support interiorly of two radiators 11 and 12 will be seen to form two cavities which are excited by balanced voltages. By the provision of these cavities with the quarter wavelength extent, it thus follows that the impedance to the cavities is infinite in value, and therefore presents substantially no load to the voltage being applied from the balancing circuit. The only load applied across the balancing circuit is that of the radiators themselves, which will be seen to be composed of the outer portions of the radiating cylinders 11 and 12.

Without delving deeply into well-known antenna theory, it is yet herein emphasized that a coaxial transmission line is an unbalanced transmission line, so that the direct connection of a voltage source through a coaxial transmission line to a dipole antenna, as by means of connecting the central conductor to one radiating element, and the shield to another, will not serve to provide a balanced voltage to the antenna. In order for a dipole antenna to radiate with a maximum radiating field lying in the perpendicular bisector of the radiating elements, it is necessary for the individual elements or radiators to be excited by voltages of equal amplitude and opposite phase. An unbalanced voltage applied to .the radiators will not accomplish this and will serve only to produce complex and relatively undesirable radiation fields about the antenna. In accordance with the present invention, there is herein combined a metallic support structure for radiating elements, together with a balancing system for energization of such elements. inasmuch as the sheath or shield of a coaxial transmission line is well known to be the equivalent of a zero voltage reference, the

present invention provides for the utilization of a dual shield return path, whereby a balanced voltage may be applied to the individual radiating elements of an antenna. Particularly desirable structures are attainable, in ac cordance with the present invention, because of the manner in which the support structure hereof and energizing connections hereof are combined into a single rigid antenna support means, through which the antenna itself may be energized. It is to be appreciated in this respect that the metallic support means of the present invention may be employed as a conduit through which a coaxial cable is passed, or, alternatively, the hollow support means may serve as the exterior sheath of a coaxial cable, with the central conductor thereof being extended through same.

Although the present invention has been above described in connecton with the support and energization of a' conventional dipole antenna, it is to be appreciated that numerous types of antennas may be supported and energized, in accordance with the present invention. In this respect, the present invention is particularly adapted to around-the-mast type antennas, which are highly desirable for various applications known in the field. Adaptation of the present invention to this type of antenna may be accomplished by the provision of cylindrical radiators about a mast, and mounted thereon by annular metallic members with cylindrical skirts extending therefrom about the mast to limit parasitic oscillations thereof. Installations of this type may employ tapered radiators of a generally conical configuration in order to limit the circumferential extent thereof at the point of energization, inasmuch as current will fail to flow in the radiator at a point directly opposite a feed point if the circumference of the radiator becomes equal to or greater than half a wavelength. Antennas of this type may be multiplied upon a single mast so that there is then provided a plurality of directional dipole antennas about a single mast, with metallic support members rigidly afllxing same to the mast. Separate coaxial cables are provided for the energization of each antenna in a multiple antenna mounting upon a single mast. In the instance wherein the total length of the radiating portion of the antenna about a mast is desired to be minimized, it is possible to limit same to one-half wavelength by forming each radiator as a pair of concentric cylinders, so as to thereby shield the inner portion, and attain the desired energization without elongation of the radiat ing length.

it is also possible to provide for purely inductive coupling of the energy to the radiators of an antenna, in accordance with the present invention, and in this respect, attention is directed to FIG. 2 of the drawings. There is shown in FIG. 2 a pair of axially alined quarter wavelength radiators 31 and 32, which will be seen to be mounted by means of an axial metallic support member 33, which is, in turn, rigidly secured to a transverse support member 34 extending generally normally to the radiators. The general antenna structure is substantially the same as that illustrated in FIG. 1 and described above, in that metallic support members 33 and 34 are provided to structurally support the antenna radiating elements 31 and 32. Electrical energization is herein provided through a coaxial cable 36, having a central conductor 37 within a sheath 38. This coaxial transmission line 36 extends through the metallic support means and further extends from the outermost end of one of the radiators back to the inner end thereof. At this point the transmission line 36 terminates with the sheath '53 in electrical contact with the radiator 32. The central conductor 37 of the transmission line is extended across the gap between the radiators 3i and 32, and into a second transmission line 39. Rather than have the central conductor 37 of the input transmission line directly connected to the left-hand radiator of the antenna, as in the abcveadescribed embodiment of the present invention, this embodiment provides for the extension of this conductor as the central conductor of the second transmission line 39. Within the second transmission line 39, there is provided a material 41 of high dielectric constant surrounding the central conductor 37. This dielectric material 41 provides a decreased velocity of trans mission along the line, so that a decreased physical length is equivalent to a quarter wavelength of the impressed voltage. As illustrated, the :dielectric material 41 and central conductor 37 extends from the right-hand end of the transmission line 39 a distance X, which is equal to one-quarter wavelength of the impressed voltage. The central conductor 37 terminates at a distance X from the right-hand edge of the radiator 31 in insulated relationship with the sheath of the second transmission line 39, and inasmuch as the extent of this transmission line is, as above noted, one-quarter wavelength, it will be seen that in accordance with established electrical theory, there is thus provided one-quarter Wavelength back from the terminus of the central conductor, the equivalent of an electrical short circuit. In this respect, conventional theory is involved, inasmuch as it is well known that a quarter wavelength of a transmission line which is open circuited at one end provides the equivalent of a short circuit at the opposite end. Consequently, there will be seen to be provided the equivalent of the connections provided in FIG. 1, with the distinction, however, that no physical connection of the central conductor 37 of the transmission line is made to the metallic elements of the antenna. A fully inductive coupling is herein afforded for energization of the radiators of the antenna, and there is thus achieved in this manner, a high degree of direct current isolation. Although the antenna structure described above in connection with FIG. 1 will be seen to afford very good protection against lightning damage, for example, it will be appreciated that the embodiment of FIG. 2 is even superior in this respect.

From the foregoing description of particular preferred embodiments of the present invention, it will be apparent that there is herein provided an improved structure for physically mounting radiating elements of an antenna. In addition, there is also provided herein an improved manner of electrically energizing an antenna, wherein a balanced-to-unbalanced transformation is required. Of particular note is the fact that the metallic structural mounting of the antenna elements hereof is combined with the coaxial transmission line energization of an antenna, so as to thereby provide fora material simplification in the mounting and energization of antennas. As above noted, the present invention is in no way limited to any particular individual type of antenna, but is, instead, applicable to a wide variety of antenna types. Thus, in addition to the types of antenna illustrated as being adapted for mounting and energization, in accordance with the present invention, particular advantage is found in the utilization of the present invention in connection with antennas including reflecting elements, and directive elements, as well as more complicated antenna arrays such as, for example, corner antennas. In each instance, the replacement of all insulators in the antenna structure with mechanically-strong metallic support members is found to afford a very substantial advantage, not only in the resultant antenna rigidity and strength, but also in the reduction ofi antenna cost. Furthermore, substantially improved antenna operation is possible through the utilization of the present invention, inasmuch as the various and numerous difficulties introduced by the presence of massive insulators are herein Wholly precludeld.

What is claimed is:

An improved antenna comprising a pair of hollow quarter-wave radiators disposed in spaced axial alinement for forming a dipole antenna, a hollow metal support tube extending axially through said radiators in rigid connection with opposite closed ends thereof and forming electrical contact therewith for supporting said radiators, a coaxial cable adapted for connection across a generator and extending through said tube and back from a closed radiator end to the other radiator end, a second cable having a sheath disposed longitudinally of said other radiator and having a dielectric material therein, and means connecting the central conductor of said first cable through said second cable a distance equal to one-quarter wavelength in said material and inductively coupling a balanced signal between adjacent ends of said radiators.

References Cited in the file of this patent UNITED STATES PATENTS 2,175,363 Roberts Oct. 10, 1939 FOREIGN PATENTS 1,000,067 Germany Jan. 3, 1957

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