US 3114913 A
Description (OCR text may contain errors)
Deg. 17, 1963 A. ALFORD 3,114,913
WING TYPE DIPOLE ANTENNA WITH U-SHAPED DIRECTOR Filed July 10, 1961 2 Sheets-Sheet l PRIOR ART HIGH HIGH T FREQUENCY I FREQUENCY I RADIATION I RADIATION ,CONDUCTING PATTERN I PATTERN 1 I I SURFACE DIPOLE/ l6 IPOLE i I? I l I E 7 I2 7 REFLECTING l2 REFLECTING SURFACE SURFACE FIGI F162 "IIII 34 36 \2I FIG. 5 I m I-IIIIIIII|E I I III IIIIIIIIIII 33 INVENTOR.
ANDREW ALFORD Dec. 17, 1963 A. ALFORD WING TYPE DIPOLE ANTENNA WITH U-SHAPED DIRECTOR Filed July 10, 1961 2 Sheets-Sheet 2 FIG. 5
ANDREW ALFORD FIG? United States Patent 3,114,913 WING TYPE DIPOLE ANTENNA WITH U-SHAPED DIRECTOR Andrew Alford, Winchester, Mass. (299 Atlantic Ave, Boston, Mass.) Filed July 10, 1961, Ser. No. 122,767 4 Claims. (Cl. 343795) The present invention relates in general to high frequency transduction and more particularly concerns a novel dipole radiator capable of maintaining maximum directivity along a prescribed direction over an exceptionally wide range of frequencies while introducing negligible reflections in a coaxial transmission line coupling it to external apparatus.
A preferred embodiment of the present invention represents a modification of the structure disclosed and claimed in US. Patent No. 2,973,517. However, the principles of this invention are generally applicable to eliminating what is termed a saddle radiation pattern in dipole antennas operated over an exceptionally wide bandwidth.
Accordingly, it is an important object of the present invention to provide an improved dipole radiator capable of maintaining a prescribed maximum directivity over a wide bandwidth while substantially properly terminating an interconnected coaxial transmission line so as to minimize reflections over this wide bandwidth.
It is another object of the invention to achieve the preceding object by the addition of a minimum amount of additional structure so that the increase in fabrication costs, Weight and bulk are maintained relatively slight.
According to the invention, means defining a conducting surface are established across the plane of symmetry separating first and second dipole elements and insulatedly separated from the elements so that the conducting surface means coacts with each element to establish an electric field for maintaining maximum directivity along the plane of symmetry over a wide bandwidth.
Numerous other features, objects and advantages of the invention will become apparent from the following specification 'when read in connection with the accompanying drawing in which:
FIG. 1 is a schematic representation of a conventional dipole in front of a reflecting sunface illustrating the undesired saddle high frequency radiation pattern obtained at certain frequencies when operating over an extended bandwidth;
FIG. 2 schematically represents the modification of the structure shown in FIG. 1 together with the improvement in high frequency radiation pattern obtained according to the invention;
FIGS. 3 and 4 show top and end views of a preferred exemplary embodiment according to the invention with the conducting surface removed to illustrate structural details; and
FIGS. 57 show top, end and side views, respectively, of the exemplary preferred embodiment according to the invention.
With reference now to the drawing and more particularly FIG. 1 thereof, there is illustrated a schematic representation of a dipole antenna 11. located before a conducting reflecting surface 12 characterized by the high frequency radiation pattern 13- with a saddle portion 14 along the plane of symmetry between the two dipole elements. This is undesirable for use in a system where maximum directivity along the plane of symmetry is required over a wide band of frequencies.
Referring to FIG. 2, there is shown a schematic representation of an improved dipole antenna radiating system capable of maintaining maximum directivity along the axis of symmetry separating the two dipole elements over an exceptionally wide bandwidth. This is accomplished by 3,114,913 Patented Dec. 17, 1963 adding the conducting surface 15, closely adjacent to the two elements 16 and 17 comprising dipole 11 symmetrical about the axis of symmetry separating the elements 16 and 17. The result of adding element 15 is to produce the high frequency radiation pattern '13 and thereby eliminate the saddle portion 14 of FIG. 1. It is believed that conducting surface 15 coacts with elements 16 and 17 to form a pair of energy gaps which radiate at higher frequencies so as to fill in the saddle portion 14. At lower frequencies the element 15 seems to have negligible effect on the satisfactory radiation characteristics of the elements 16 and 17 alone. The length of elements 16 and 17 is preferably of the order of a quanter wavelength at the center frequency of the operating band while the length of conducting surface 15 along the direction of the length of elements 16 and 17 is preferably less than the length of either of elements 16 and 17 and is separated from each of these elements by less than the length of either.
With reference now to FIGS. 3 and 4, there are shown top and end views, respectively, of a dipole radiator comprising an exemplary embodiment of the best mode now contemplated for practicing the invention with the conducting surface 15 removed so that structural details may be illustnated. The dimensions in the drawing as filed are true scale drawings of the Alford Manufacturing Company type 1063 broad band microwave dipole which maintains the desired directivity and low VSWR over a frequency range from 1,000 to 2,200 megacyoles. The length of each dipole radiating element is 178 inches, corresponding to a quarter wavelength at 1,575 megacycles, a frequency just above the geometric mean frequency of the band and just below the arithmetic mean.
The structure illustrated in FIGS. 3 and 4 comprises primarily an aluminum casting 21 with a coaxial terminal pair 32 screwed to the base 33 of the casting. A left leg 34 and right leg 35 extend from base 33 for supporting dipole elements 16 and 17, respectively. Legs 34 and 35 are joined by the faceted sections 36 and 37 and coact therewith to form the outside conductor of an extension of the coaxial transmission line attached to coaxial terminal pair 32. The inner conductor of this coaxial transmission line extension is connected to dipole element 17 by a segment 33. Observe that segment 38 includes a portion 41 generally parallel to both legs 34 and 35 but closer to leg 34 than to leg 35. Segment 38 coacts with legs 34 and 35 to form a balun for converting an unbalanced signal between the inner and outer conductors of the coaxial transmission line extension into a balanced signal developed across the top inside surfaces 42 and 43 of legs 34 and 35, respectively, adjacent to dipole elements 16 and 17, respectively. An insulator 40 is seated within faceted sections 36 and 37 for insulatedly supporting the inner conductor therein. It has been discovered that positioning straight portion 41 of segment 38 asymmetrically as shown improves the properties of the balun in matching the impedance of the radiating structure to that of the coaxial transmission line over the desired wide bandwidth.
The inside portions 44 and 45 of radiating elements 16 and 17, respectively, taper gradually to the increased thickness of legs 34 and 35. Elements 16 and 17 are trapezoidal. Their inwardly tapering sides 47 and 48, respectively, smoothly join the tapered end surfaces 51 and 52, respectively, of legs 34 and 35, respectively. Legs 34 and 35 are tapped at a number of locations, such as 53 for accommodating screws used to support. conducting surface 15. Base 33 is formed with a number of openings 54 for accommodating bolts securing it to the reflecting surface 12. The reflecting surface 12, not illustrated in detail here, may be the well-known tri-plane reflector. The distance between the feedpoint where element 33 is connected to leg 35 and the portion of the reflecting surface essentially coplanar with the junction between coaxial terminal pair 32 and base 33 is of the order of a quarter wavelength at the same frequency as the elements 16 and 17.
Referring to FIGS. 57, there are shown top, end and side views, respectively of the exemplary embodiment of the invention with the conducting surface 15 positioned according to the invention and supported by legs 34 and 35. Conducting surface 15 is generally U-shaped with Teflon screws 61 and Teflon annular spacers 62 securing conducting surface 15 in insulatedly spaced relationship with respect to elements 16 and 17 symmetrical about the plane of symmetry included by elements 16 and i7 and the axis of symmetry separating these elements. A pair of conducting rods 63 and 64 are secured to conducting surface 15 by screws 65 as shown for adding rigidity to the U-shaped surface and functioning electrically to help maintain the impedance match over the desired bandwidth.
There has been described a novel dipole antenna structure capable of maintaininga single major lobe directivity aligned in a prescribed direction over an exceptionally wide bandwidth while maintaining the VSWR in a connecting transmission line relatively low. it is evident that those skilled in the art may now make numerous modifications of and departures from the specific exemplary embodiment described herein, for example, by using different types of dipoles and conducting surfaces of different forms, without departing from the inventive concepts. Consequently, the invention is to be construed as limited only by the spirit and scope of the appended claims.
What is claimed is:
1. High frequency radiating apparatus characterized by a radiation pattern having a maximum along a prescribed direction over a frequency range of the order of 2:1 comprising, first and second like generally planar dipole radiating elements, each having a length corresponding substantially to a quarter wavelength at a frequency between the arithmetic and geometric means of said frequency range and symmetrical about a first plane of symetry generally perpendicular to a second plane of symmetry included by said elements, first and second legs generally parallel to and symmetrical about said first plane inside of and connected to respective ones of said first and second radiating elements, said elements and said legs defining a generally Y-shaped gap symmetrical about said first plane, a generally U-shaped conducting surface covering the central portion of said Y-shaped gap insulatedly separated from said elements and said legs and symmetrical about said first and second planes, and a reflecting surface separated from said radiating elements by said legs and spaced from said elements substantially by said quarter wavelength.
2. High frequency radiating apparatus in accordance with claim 1 and further comprising first and second conducting rods connected from one leg of said U-shaped conducting surface to the other across said Y-shaped gap symmetrical about said first and second planes.
3. High frequency radiating apparatus in accordance with claim 1 and further comprising, a coaxial transmission line section having an inner conductor and an outer conductor, and a balun comprising said legs for transducing an unbalanced signal across said inner and outer conductors with a balanced signal between said elements.
4. High frequency apparatus in accordance with claim 3 wherein said balun further comprises, a conducting segment having a first portion generally parallel to said legs and a second portion connected to one of said elements, said first portion being closer to the other of said elements than to said one element.
References Qited in the file of this patent UNITED STATES PATENTS 2,485,138 Carter Oct. 18, 1949 2,726,390 Weiss Dec. 6, 1955 2,886,813 Hings May 12, 1959 2,973,517 Watts Feb. 28, 1961