US 3550145 A
Description (OCR text may contain errors)
Dec. 22,1910 CHEN To m 3,550,145
MANIPOLE BROADBAND ANTENNA Filed Aug. 5, 1968 MHZ INVENTOR, CHEN T0 TA I.
BY: m! )s W 14f l/ ATTORNEYS.
United States Patent 015cc 3,550,145 Patented Dec. 22, 1970 3,550,145 MANIPOLE BROADBAND ANTENNA Chen To Tai, Ann Arbor, Mich., assignor, by mesne assignments, to the United States of America as represented by the Secretary of the Army Filed Aug. 5, 1968, Ser. No. 750,144 Int. Cl. H01q 21/00, 9/38, N50
US. Cl. 343-826 Claims ABSTRACT OF THE DISCLOSURE BACKGROUND OF THE INVENTION This invention relates to the field of antennas, and particularly to the field of broadband antennas in the VHF- UHF region. The antenna of the instant invention may be used to both transmit and receive in the designed spectrum although signals of other frequencies may be employed with predictably poorer results.
Various types of vertical broadband antennas have been constructed in the past including those having a plurality of rods of different lengths. It is significant to note, however, that none of the vertical antenna systems heretofore rely on the principal of linear tapering of elements randomly attached to a metallic ground plane with each being connected to the center conductor of a coaxial transmission cable while the outer conductor of the same coaxial transmission line is connected to the ground plane thereby producing a truly broadband antenna. One type of multi-element antenna that has been designed spaced the rods or elements about the circumference of hollow cylindrical supports; however, such device fails to achieve the broadband characteristics of the instant combination employing the principle linear tapering and the greater ease of construction flowing from randor spacing on a ground plane. Other types of variable length rnulti-element antennas have been designed but are generally more complex than that of the instant invention.
SUMMARY OF THE INVENTION It is the primary object of this invention to fabricate an antenna system employing a novel combination of elements and principles thereby producing an antenna of especially broadband design. The antenna herein disclosed can replace a single monopole used on many vehicles as a broadband antenna and can be constructed with relative case when compared to other multi-element antennas.
It is a further object of the instant invention to produce a compact, omni-directional VHF-UHF antenna having a VSWR of less than 3:1 over a 10:1 frequency band.
It will be appreciated by those skilled in the art that the particular antenna herein disclosed is of rugged construction with each element firmly and independently supported on a ground plane thereby enabling the antenna to be used in environments heretofore impractical or impossible. Dielectric spacers may be used for reinforcement if necessary, however, such construction forms no part of the present invention.
BRIEF DESCRIPTION OF THE DRAWING The exact nature of this invention will be readily apparent from consideration of the following specification relating to the annexed drawing in which:
FIG. 1 is a perspective view of the broadband antenna of the present invention.
FIG. 2 is a partial cross-section of FIG. 1 taken through the center of the circular ground plane to which the vertical elements are mounted.
FIG. 3 is a graph of the radiation pattern of the antenna of the instant invention taken at 3.0K mcs. with H-plane polarization and a pattern range of 30 feet.
FIG. 4 is a graph of the VSWR characteristics of the bipole antenna of the instant invention showing VSWR versus frequency in mHz.
DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to the drawings, wherein like reference characters designate like or corresponding parts throughout the views, there is shown in FIG. 1 a perspective view of the antenna system of the preferred embodiment wherein antenna elements 11 are supported on ground plane 10. The elements 11 are independently mounted on ground plane 10 in the sense that they do not mutually support each other but are solely supported by said ground plane 10. In one of the antennas constructed, ground plane 10 was fabricated of aluminum that was approximately Aa inch thick and 2 inches in diameter, although it is to be understood that these dimensions may be varied as well as the specific material from which the ground plane 10 and rods 11 are constructed. In the preferred embodiment, rods 11 were constructed of #18 copper wire of varying lengths and employing the principal of linear tapering, that is, gradually tapering the rods in a linear manner from one larger end 16 where the rods 11 join the ground plane 10 to the other or free end 17. Further in the preferred embodiment, 47 elements 11 were employed, the shortest being 25 mm. in length and each successive element was 5 mm. longer so that the elements 11 were 25, 30, 35, etc., until the last and. longest element was 250 mm. long, thereby giving the omnidirectional and broadbank characteristics shown in FIGS. 3 and 4.
It is seen from FIG. 2, a partial cross-section taken through the center of the ground plane 10, that the elements 11 are fed by the center conductor 14 of a coaxial cable with the outer conductor 13 being connected to the ground plane 10. At junction 15, the conductor 14 is split to feed each of the elements 11 through insulation 12.
Obviously, numerous modifications or alterations could be made to the elements of the preferred embodiment of the instant invention without departing from the spirit or scope of the invention as set forth in the appended claims. Various modifications might include, but not by way of limitation, changes in size or materials of construction. Two areas of interest from FIG. 4 appear to be at 600 and 3000 mHz. Studies suggest that several longer elements 11, in excess of 250 mm., might be employed to minimize the VSWR variation at 600 mHz. while additional shorter elements 11 might be employed to minimize the VSWR variation the higher frequency. The elements 11 are randomly varied on the ground plane 10 will be substantially no change in the VSWR as shown in FIG. 4.
What is claimed is:
1. A broadband antenna system for radiating and receiving electromagnetic energy comprising:
a metallic base employed as a ground plane and as a support means; and,
a plurality of linearly tapered cylindrical elements of varying lengths randomly and independently mounted on said base for radiatiing and receiving said electromagnetic energy.
3 2. A broadband antenna according to claim 1 and further comprising:
coaxial means for feeding said elements such that the center conductor of said means is electrically connected to each of said elements and the outer conductor of said means is electrically connected to said ground plane. 3. A broadband antenna according to claim 1 and further comprising:
each of said tapered elements having two ends, one
end being larger than the other end; and, said elements being positioned on said ground plane in such a manner that said one larger end is mounted adjacent said ground plane. 4. A broadband antenna according to claim 2 and further comprising:
each of said tapered elements having two ends, one
end being larger than the other end; and, said elements being positioned on said ground plane in such a manner that said one larger end is mounted adjacent said ground plane. 5. A broadband antenna according to claim 4 wherein: said ground plane is constructed of aluminum and is of a generally circular configuration; and,
said plurality of elements vary in length from 25 mm.
to 250 mm.
References Cited UNITED STATES PATENTS 1,388,441 8/1921 Pupin et a1 343-826X 2,206,821 7/1940 Mydlil 343828X 2,239,724 4/1941 Lindenblad 343828X 2,250,531 7/1'941 Hansell 343826 2,267,889 12/ 194'1 Aubert 34382-6 2,996,718 8/1961 Foley 343825 FOREIGN PATENTS 414,296 8/1934 Great Britain 343830 52,479 5/1944 France 343-826 HERMAN KARL SAALBACH, Primary Examiner T. VEZEAU, Assistant Examiner US. Cl. X.R. 343830, 863, 893