US 3358287 A
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Dec. 12, 1967 H. BRUECKMANN BROADBAND DUAL-POLARIZED ANTENNA 2 Sheets-Sheet 1 Filed Jan.
INVENTOR, HEL MUT BRUECKMANN.
w: ,m& M ATTORNEYS Dec. 12, 1967 H. BRUECKMANN BROADBAND DUAL-POLARIZED ANTENNA 2 Sheets-Sheet 2 Filed Jan. 6, 1965 FIG. 4
HELMUT BRUECKMANN BY W1- I W M C ATTORNEYS United States Patent 3,358,287 BROADBAND DUAL-POLARIZED ANTENNA Helmpt Brueckmann, Little Silver, N.J., assignor to the United States of America as represented by the Secretary of the Army Filed Jan. 6, 1965, Ser. No. 423,881 8 Claims. (Cl. 343-786) ABSTRACT OF THE DISlZ'LOSURE A dual-polarized turnstile antenna having two sets of orthogonally spaced dipoles. A pair of inputs are coupled to the antenna via a transformer arrangement such that two adjacent antenna elements are fed in phase with each other and fed against the other two elements as viewed from one of the inputs. As viewed from the other input a difierent set of two adjacent antenna elements are fed in phase with each other and fed against the other two elements.
The invention described herein may be manufactured and used by or for the Government for governmental purposes without the payment of any royalty thereon.
The present invention relates to improvements in antennas and the like and more particularly to an improved feed system for broadbanding dual-polarized antennas.
It is well known that any type and orientation of polarization of electromagnetic waves can be obtained by arranging two dipoles orthogonally about a common center and exciting them in the proper phase and ampli tude relationship. Such an arrangement is commonly referred to as a turnstile antenna and falls in the general classification of dual-polarized antennas, i.e., an antenna having two planes of polarization which are perpendicular to each other. It is now standard practice to thicken the antenna elements or conductors as one means for broadbanding turnstile antennas. This method, however, has the disadvantage of increasing wind drag, ice load, etc. compared to narrowband antennas having relatively thin antenna elements. As a result, construction costs including the cost of the support are relatively high. Another standard method of broadbanding such elements is to increase the number of antenna elements. However, it is obvious that this method which results in an increased number of elements has the same disadvantages as does the method of thickening the poles.
It is, therefore, the primary object of the present invention to improve the broadband properties of dualpolarized antennas while maintaining the construction costs low.
More specifically, this object is attained by placing the polarization planes of the standard narrow band dual polarized antennas at an angle of 45 degrees against the principal axes of the antenna elements by means of hybrid or bridge coupling circuits in the feed system.
The exact nature of this invention as well as other objects and advantages thereof will be readily apparent from consideration of the following specification relating to the annexed drawing, in which:
FIG. 1 is a diagrammatic view of one embodiment of the invention;
FIG. 2 is a diagrammatic view of another form of the invention;
FIG. 3 is a diagrammatic view of the device of FIG. 2 mounted in an array;
FIG. 4 is a perspective view, partly diagrammatic, of still another form of the invention; and
FIG. 5 is a section of the device shown in FIG. 4.
Referring now to the drawings, wherein like reference characters designate like or corresponding parts through Patented Dec. 12, 1967' out the several views, there is shown in FIG. 1 a dualpolarized turnstile antenna 10 comprising two sets of orthogonally spaced dipoles crossed at their centers. Antenna elements 12 and 13 make up one of the sets of dipoles and elements 14 and 15 make up the other set. Elements 12, 13, 14, and 15 lie in the same plane and are, therefore, arranged in fourfold axial symmetry. A first transformer 17 has its secondary coupled between the feed points of elements 12 and 15. A second transformer 18 is shielded from the first transformer 17 and has its secondary coupled between the feed points of elements 13 and 14. The primaries of transformers 17 and 18 are connected in parallel with each other and across a first pair of input terminals 20 and 21. A second pair of input terminals 22 and 23 are connected to the midpoints of the secondary windings of transformers 17 and 18 respectively. The sense of the windings on transformers 17 and 18 are such that poles 13 and 15 will be fed in phase and fed against poles 14 and 12 as seen by input terminals 20 and 21. The resulting plane of polarization for input terminals 20 and 21 will, therefore, be inclined at 45 degrees with respect to the antenna poles and extend from the upper right side to the lower left side as viewed in FIG. 1. As seen from input terminals 22 and 23, elements 13 and 14 will be fed in phase and fed against elements 12 and 15 which are also fed in phase. This is true, because the inputs 22 and 23 are connected to the midpoints of transformers 17 and 18, thereby causing the effect of one half of the transformer to cancel out the elfect of its other half. The plane of polarization for inputs 22 and 23 will, therefore, be perpendicular to the plane of polarization for inputs 20 and 21.
From the impedance viewpoint, each input is effectively feeding a dipole wherein each dipole half consists of two conductors or antenna elements. For example, with respect to inputs 20 and 21, the combination of elements 13 and 15 are equivalent to a dipole half while the combination of elements 12 and 14 are equivalent to the other half. Such an arrangement will result in a bandwidth which is wider thanthe bandwidth of standard turnstile antennas wherein each input feeds only two conductors or antenna elements as is well known from conventional broad-banding techniques. In other words, because each input feeds one pair of antenna elements against another pair of elements the equivalent Q of the antenna is lower than an antenna having only one element fed against another, assuming, of course, equal thickness for the elements. Because the Q is lower, the bandwidth will obviously be broader.
The device of FIG. 2 utilizes the same principles described above for the device of FIG. 1. However, a slightly different feed system is used. The feed points of elements 12, 13, 14, and 15 are connected by chokes 25, 26, 27, and 28. These chokes are shielded from each other. However, each choke is tightly coupled to itself as indicated by the parallel lines which represents a ferrite core or the like. The input terminals 20, 21, 22, and 23 are each connected to the midpoints of chokes 25, 26, 27, and 28 respectively. It is, therefore, evident that with respect to input 20, for example, one half of choke 25 will cancel out the effect of the other half of choke 25 and input 20 will be coupled to elements 13 and 15 through a low impedance. However, chokes 27 and 28 will present a high impedance to input terminal 20. In a like manner a low impedance will couple terminal 21 to elements 12 and 14, terminal 23 to elements 13 and 14, and terminal 22 to elements 12 and 15. We, therefore, have a dual-polarized antenna with two orthogonal lanes of polarization inclined at an angle of 45 degrees with respect to the elements 12 and 15. This results in the same situation as was described for the device of FIG. 1. Of course, as in standard turnstile antennas, the resultpair of axially spaced, dual-polarized antennas fed in phase opposition. Such arrays, beyond being directional,
are also useful for creating a neutral axis wherein the antenna mast and feed lines are mounted without affecting the radiation. Since the antennas are fed in phase opposition the neutral axis will be midway between the antennas. The manner of feeding such an array to obtain phase opposition is shown in FIG. 3, i.e., corresponding elements on the antennas are connected to the same input terminals but in a reversed manner. For example, the pair of elements 12 and 15 are connected to terminal 22" while elements 12" and 15" are connected to terminal 23.
FIGS. 1-3 show the antenna elements in the form of linear dipoles. Of course, these elements are only representative and may be replaced by, end-loaded dipoles, folded dipoles, loop antennas, biconical antennas, etc. The principles of the invention may be carried out as long as there are four identical antenna elements arranged in fourfold axial symmetry.
FIGS. 4 and show the principles of the invention applied to a square horn antenna having four antenna elements or tapered ridges 30, 31, 32, and 33 arranged in fourfold axial symmetry inside a square waveguide section 34. One end of the section 34 is terminated in a quarter-wave cavity 35 and the other end is connected to the throat of afiared horn 36. Ridges 30-33 at the wide end adjacent cavity 35 are connected to each other by chokes 25, 26, 27, and 28. A pair of input lines in the form of coaxial lines 37 and 38 pass through the 1 rear wall of cavity and have their outer conductors connected to the midpoints of chokes 2 7and 2S respectively. The center conductors of lines 37 and 38 are connected to the midpoints of chokes 28 and 26 and to the shorted quarter-wave stubs 39 and 40 respectively. Quarter-wave stubs 39 and 40 are in effect dummy coaxial conductors and provide a balanced transformation from lines 37 and 38 respectively to the ridges 30, 31, 32, and 33(With respect to input lines 37, ridges 31 and 32 will be fed in phase and against ridges 30 and 33. With respect to input line 38 ridges 32 and 33 will be fed in phase and against ridges 30 and 31. 7
It should 'be understood of course, that the foregoing disclosure relates to only preferred embodiments of the invention and that numerous modifications or alterations may be made therein Without departing from the spirit pended claims.
What is claimed is:
1. A daul-polarized antenna comprising; four identical antenna elements arranged in fourfold axial symmetry; first and second inputs; first and second transformers, said first input connected across the primaries of said transformers; the secondary of said first transformer connected between one adjacent pair of said antenna elements; the secondary of said second transformer connected between the other pair of said antenna elements opposed thereto; and the terminals of said second input connected to the midpoints of said secondaries of said first and second transformers respectively.
2. The antenna according to claim 1, and wherein said four antenna elements form two linear dipole antennas mounted normal to each other and intersecting at their midpoints.
3. The antenna according to claim 1, and wherein said four antenna elements are coupled to a horn antenna.
4. The antenna according to claim 3, and wherein said horn is square shaped and said elements are tapered ridges mounted in a square waveguide which terminates in a cavity at one end and is connected to said horn'at the other end thereof.
5. A dual-polarized antenna comprising four antenna elements arranged in fourfold axial symmetry; first and second inputs; four choke coils; each said coil connected between a different pair of adjacent antenna elements; said first input connected to the midpoints of onepair of opposed coils; and said second input connected to the midpoints of the other pair of opposed coils.
6. The antenna according to claim 5 and wherein said four antenna elements form two linear dipole antennas mounted normal to each other and intersecting at their midpoints.
7. The antenna according to claim 5 and wherein said four antenna elements are coupled to a horn antenna. 8. The antenna according to claim 7, and wherein said horn is square shaped and said elements are tapered ridges mounted in a square waveguide which terminates in a cavity at one end and is connected to said horn at the other end thereof.
References Cited UNITED STATES PATENTS 2,374,271 4/1945 Brown 343798 2,581,352 1/1952 Bliss 343-797 3,248,736 4/ 1966 Bohar 343-797 ELI. LIEBERMAN, Primary Examiner.