US 3611398 A
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United States Patent Geroge l-l. Schnetzer Albuquerque, N. Mex.
Mar. 31, 1970 Oct. 5, 1971 The United States of America as represented by the United States Atomic Energy Commission  Inventor [21 Appl. No.  Filed  Patented  Assignee  BALANCED DIPOLE ANTENNA 6 Claims, 5 Drawing Figs.
 U.S. Cl 343/799, 343/807, 343/822  Int. Cl H011; 21/20 lox l 30b 34 i  Field of Search 343/793, 794, 795, 799, 807, 822
 References Cited UNITED STATES PATENTS 3,348,228 10/1967 Melancon 343/799 Primary Examiner-Eli Lieberman Attorney-Roland A. Anderson ABSTRACT: A balanced dipole antenna array comprising radiators disposed in spaced-apart parallel planes, each including at least one conductor spoke from which extends a conductive rim or arm that terminates in space, the radiators being in axial alignment and rims or arms extending in opposite directions.
PATENTED um 5:91: $611,398
FIG. 3b PIC-3.36
INVENTOR. GEORGE H. SCHNETZER BALANCED DIPOLE ANTENNA BACKGROUND OF INVENTION There are various loop, dipole or the like antenna arrangements which may be used to radiate horizontally polarized electromagnetic waves with an omnidirectional radiation pattern. Prior antenna arrangements having this capability have suffered from one or more limitations, such as, the antennas have been difficult to manufacture, the antenna size may be too large for some applications, and theantenna may be fragile or otherwise easily damaged under high physical loads or stresses. These and other antennas may also present a lowinput impedance and consequently require some impedance transformers or matching to the signal generator or signal transmission line which adds to the overall complexity,- size and cost of the antenna system. There are applications, such as space applications, missile guidance systems, and the like where it may be desirable to provide an antenna having small size and high input impedance as well as ruggedness, simplicity and ease of manufacture.
Such applications frequently require horizontally polarized antennas for high frequency signals, such as for signals in the X-band (9 to kilomegahertz). Prior horizontally polarized X-band antennas are generally either slotted cylinders or crossed dipoles. A slotted cylinder antenna may be made by cutting longitudinal slots in a circular waveguide. At this frequency the circular waveguide must be over 1 inch in diameter and a few inches long. A crossed dipole antenna requires a circuit to provide a 90 phase difference between the currents and the two dipoles. This circuit requires space and increases the complexity of the antenna. Various other antenna types may be used to produce horizontal polarization at other frequency ranges but the problems of fabrication in small size desired for these applications make them impractical. Further, many of these antenna structures or arrays are unbalanced and may be characterized for the most part by awkwardness of supply line connections, necessity of substan tial amounts of insulation in various positions, and difficulty of providing adequate mechanical support.
SUMMARY OF INVENTION In view of the limitations of the prior art as noted above, it is an object of this invention to provide a novel, balanced, dipole-type antenna array.
It is a further object of this invention to provide such an antenna having a high-input impedance.
It is a still further object of this invention to provide such an antenna having a relatively small size for the frequency bandwidth of the antenna.
It is a still further object of this invention to provide such an antenna of simple and rugged design.
Various other objects and advantages will appear from the following description of this invention, and most novel features will be particularly pointed out hereinafter in connection with the appended claims.
It will be understood that various changes in the details, materials and arrangements of the parts, which are herein described and illustrated in order to explain the nature of the invention, may be made by those skilled in the art.
The invention comprises a pair of antenna radiators each including at least one conductor extending from a central location with each conductor including an arm extending from the end thereof about the central location terminating in space, each of said radiators being aligned with the arms extending in opposite directions and in overlying and underlying relationship, together with means for connecting an electrical signal between central locations.
DESCRIPTION OF DRAWING The invention is illustrated in the accompanying drawing wherein:
FIG. 1 is a perspective exploded view showing one form of the antenna array of this invention;
DETAILED DESCRIPTION Referring to FIG. 1, antenna includes a pair of radiators l2 and 14 disposed in parallel planes and stacked one above the other with an insulator 16 disposed therebetween; Radiator 12 includes one or more or a plurality of radially extending spokes or conductors 20a, 20b, 20c and 20d extending from a central location or common terminal 22. Each conductor includes a conductive arm extending about central location 22 from the end or a distal point of the radial conductor to a position adjacent to but terminating in space before the next adjacent radial conductor, such as shown by rims or arms 24a, 24b, 24c and 24d. Each of said arms extends in the same direction, as shown, incurved or straight fashion to form a substantially completely enclosed annular conductive ring coaxially about central location 22. Radiator 12 may be providedwith a central aperture or bore 26 for appropriate connection to the signal feed transmission line 28. Radiator 14 may include corresponding radial spokes or conductors 30a, 30b, 30c and 30d, central terminal 32, conductive arms 34a, 34b, 34c and 34d and central aperture 36. Each of the conductive arms of element 14 are directed in the same direction about the array but opposite to the direction of the conductive arms of radiator 12. The respective radiators may be aligned so that the conductive arms, such as conductive arms 24b and 34b are directly above and below or adjacent to and underlying each other. In such a position, adjacent radial conductors 20a and 30b or radial conductor pairs will be directly above each other at the central locations 32 and 22 and taper or diverge outwardly to the conductive arms.
The radiator arrangement may be connected to an ap- 1 propriate signal source (not shown), such as a radio transmitter and/or receiver or other high frequency or the like signal source, through transmission line 28 as shown in FIG. 2. Transmission line 28 may be any appropriate coaxial line matched to the impedance of the signal source with a central conductor 40, an annular insulator 42, a braided shield conductor 44 and an outer protective insulator 46. Transmission line 28 may be connected to the antenna array by passing through central conductor 40 through bore 48 in insulator l6 and soldering or brazing it to radiator 12 via bore 26. The central location or terminal 32 of radiator I4 may then be appropriately connected or coupled to braid 44. A particularly appropriate coupling may be achieved by dimensioning bore 36 in radiator 14 to receive annular insulator 42 and a rigid conductive coupling 50, or a part thereof, which in turn may be connected to braid 44 by any appropriate pressure, soldered or brazed fit, as shown. If desired, coupling 50 may be provided with a flange or mounting member 52 which in turn carries or supports a radiation transparent protective housing or radome 54.
With this arrangement. conductive arm 24a forms a dipole with conductive arm 34b while conductive arm 34a forms a dipole with conductive arm 24d, etc., when the transmission line 28 is suitably energized by the signal source. Each of the conductive arms is of equal length with an electrical length of about one-quarter wavelength or less at the transmission frequency to provide a dipole of about one-half wavelength. Since conductive arm 24a is identical to conductive arm 34b except for direction, the conductive arms form balanced dipoles. The adjacent conductive radial conductors form the respective radiators are of equal length, such as conductors 20a and 30a, and carry equal but opposite electric currents which cancel each other with respect to radiation patterns generated thereby.
The tapered or diverging of the adjacent radial conductors and dipole arrangement provides good impedance matching therebetween with an impedance approaching that of the transmission line with a consequently low-voltage standing wave ratio.
Using a four-dipole array as shown in FIGS. 1 and 2, dimensioned to transmit X-band frequencies, the antenna array may be about ye-inch outer diameter with conductive arms about one-quarter inch in length and radial conductors about oneeighth inch in length. The respective radiators may be convenient thickness which provides the desired rigidity and ease of manufacture, such as about 1/16- to l/8-inch thick. The thickness of insulator 16 may be selected, depending upon the insulative material, to achieve the optimum impedance for the antenna. Using a polytetrafluoroethylene insulative material, insulator l6 thickness may range from about 0.050 to 0.100 inches. With these relative dimensions, the radial currents cancel themselves and produce negligible radiation while the currents on the ends of the arms are in the same direction for both radiators and produce a ring a current. This current is in phase or substantially in phase all around the radiators producing a radiation pattern which is uniform in the azimuth plane, i.e., the plane of the radiators. The vertical separation of radiators may produce a small vertical component in the radiated field which may decrease with decreasing spacing. If the spacing between radiators is increased and the size of the radiators appropriately adjusted, the radiator may produce a circular polarized radiated field.
Transmitting in the X-band with an antenna dimensioned as noted above, the antenna exhibited a voltage standing wave ratio of less than 1.4 with an impedance of about 50 ohms. The antenna radiated horizontally polarized electromagnetic waves with an omnidirectional radiation pattern.
The antenna radiators 12 and 14 may be made of any appropriate conductive material, such as copper, aluminum or brass. It may be conveniently formed from stock metal rods by boring or otherwise cutting out the necessary gaps to form the radial conductors and arms in the configuration shown, as well as the central bores and then cutting individual radiators from the shaped rod. Each of the radiators may differ only in the diameter of central bores 26 and 36 with radiator 14 merely turned over" to position the conductive arms in the opposite direction. The individual elements may then be readily and easily mounted and fastened together.
if desired, other configurations may be utilized, depending upon the desired application, using two radiators with one or more radial conductors and conductive arms (and consequently two or more dipoles) as shown by the diagrammatically illustrated radiators in FIGS. 3a, 3b and 3c, with straight or arcuate conductive arms of one radiator underlying arms of the other.- The fewer the dipoles utilized, the smaller the overall dimensions of each radiator and the antenna with possibly decreasing uniformity of radiating wave patterns.
What is claimed is:
l. A high frequency signal balanced antenna comprising a first radiator disposed in a first plane having a plurality of equally spaced conductors extending radially from a central location and each connecting with a conductive peripheral arm extending from the end of each said radial conductor in the same direction about said central location terminating in space adjacent an adjoining conductor; a second radiator disposed in a second plane generally parallel to said first plane having a plurality of equally spaced conductors extendingv radially from a central location with each conductor angularly offset from an adjacent conductor of said first radiator to form a tapered transmission line therewith and each connecting with a conductive peripheral arm extending from the end of each said radial conductor in the same direction opposite to and underlying and coextensive with that of an arm of said first radiator and terminating in space adjacent an adjoining conductor of said second radiator, the arms of adjacent angularly offset conductors of said first and second radiators forming a dipole with each of said dipole arms overlapping and coextensive with an adjoining dipole for one-half a dipole;
means intermediate said first and second planes for insulating said first radlator from said second radiator; and means for connecting said high frequency signal between the central location of said first radiator and the central location of said second radiator.
2. The antenna of claim I wherein said connecting means including a coaxial cable feed line having its central conductor coupled to the central location of said first radiator and its outer conductor coupled to the central location of said second radiator.
3. The antenna of claim 1 wherein said arms are arcuate.
4. The antenna of claim 3 wherein said dipole antenna is up to about onehalf wavelength long.
5. The antenna of claim I having four arcuate arms in each radiator and being less than one-half wavelength in diameter.
6. The antenna of claim I wherein said first and second radiators are spaced less than one-quarter wavelength apart.