US2478913A - Dipole antenna - Google Patents

Description

Au 16, 1949. GOLDBERG 2,478,913

DIPOLE ANTENNA Filed Feb. 7, 1944 Sheets-Sheet 1 FIG. I

I6 I? e 8 21 20 Iii T l5 I4- k MOTOR m x x xlfl n 4 INVENTOR.

A TTOANE Y 16, 1949- v H. GOLDBERG 2,478,913

. DIPOLE ANTENNA Fild Feb. 7, 1944 s Sheets-Sheet z.

FIG-- 20,

INVENTOR, HAROLD GOLDBERG A TTORNEY H. GOLDBERG DIPOLE ANTENNA Aug. 16, 1949.

3 Sheets-Sheet 5 Filed Feb. '7, 1944 FIG.

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FREQU ENCY IN VENTOR. 14/119040 GOLDBERG A TTORN E Y Patented Aug. 16, 1949 UNITED STATES PATENT OFFICE DIPOLE ANTENNA Harold Goldberg, Irondequoit, N. Y., assignor to Stromberg-Carlson Company, Rochester, N. Y., a corporation of New York Application February "I, 1944, Serial No. 521,456

4 Claims.

This invention relates to antennas and more particularly to dipole antenna assemblies.

In the pulse echo type of position indicating, it is customary to feed the exploring impulses to and to receive the reflected impulses on a dipole antenna assembly. This assembly comprises a pair of rigid coaxial conductors projecting from a fixed parabolic reflector, along the axis of symmetry thereof to a point where a dipole member other hand, has not been indicated, since metal would short circuit these conductors and it was therefore believed that the antenna assembly would be rendered inoperative. It has been discovered, however, that a metal support of suitable dimensions when joined to the mentioned coaxial conductors in the proper location therebetween, not only eiiects static and dynamic balancing thereof but improves the electrical characteristics of the assembly.

Dipole antenna assemblies of the mentioned type are so constructed that the side lobes of the antenna pattern will be of minimum size and the principal axis of the main or beam lobe of said pattern will define with the axis of rotation of the assembly, an angle which is herein referred to as the angle of skew." This angle has formerly been controlled, other factors being equal, by a choke which in form was a cylindrical shell conductively joined at one end thereof, in coaxial relation to the outer conductor of the P ir, bein in effect a short-circuited coaxial line. Ithas further been discovered that if the choke is caused to flare in the direction of the dipole members, instead of retaining its conventional cylindrical shape, the dipole assembly will have markedly improved electrical characteristics.

For a clearer understanding of the invention, reference is made to the following description and claims when taken with the drawings in which:

Fig. 1 is a vertical longitudinal section of the dipole antenna assembly of the present invention; Figs. 2, 2a and 2b are enlarged sectional views 2 of varied forms of a support mounted at th junction of the respective dipole members with their respective conductors;

Fig. 3 is a chart showing the change effected in the standing wave ratio by the present invention, which ratio is an index of impedance match, produced by a given dipole assembly as'the diameter of the cylindrical type of support is varied; I

Fig. 4 is an enlarged perspective view of the choke of Fig. 1; and Figs. 4a, 4b and 4c are enlarged perspective views of modified forms of tapered chokes together with the related coaxial conductor on which each is mounted; and

Fig. 5 is a chart useful in explaining the effects of such tapered chokes.

In the drawings, the numeral 5 designates an aluminum or similar light metal reflector, the inner surface of which conforms to a paraboloid of revolution. This reflector has a central hollow support 6 extending along its axis of symmetry XX. Through this support, there extend the rigid coaxial conductors 8 and 9. These conductors of which conductor 8 is a central rod or tube and the conductor 9 is a tube, are uniformly spaced from each other to serve as a so-called coaxial line. This coaxial line which thus projects along the axis of symmetry X-X of the reflector is mounted on suitable bearings I0 in support 6 to be rotated by motor M around this axis. The end portion of the tube 9 has a conducting rod-like dipole member ll joined to the exterior thereof and extending at right angles thereto. Similarly, the rod 8 has a second dipole member I2 joined thereto to project through an opening [3 in the tube and to extend in alignment with the member II but in the opposite direction with respect thereto. The free end of the coaxial line is closed by a metal, short-circuiting plug [4 which supports the rod 8 in fixed relation with respect to the tube 9 and functions as a reactance for tuning the antenna. The tube 9 has a flat disc-like reflector l5 mounted thereon in parallel relation to the dipole members. The rotatable portion of the coaxial line, comprising the inner conductor 8 and the outer conductor 9, is capacitively coupled by the sleeves l6 and I! to a fixed portion of a coaxial line comprising the rod or tube 8a and the tubular conductor 9a, which extends at right angles to axis X-X.

In accordance with this invention, the inner conductor 8 and the tubular outer conductor 9 are conductively joined together by a solid metal member l8, of suitable cross section and shape,

solidly joining the inner conductor 8 and the outer tubular conductor 9,, as shown in Fig. 2.

In the modified form of the invention, shown in Fig. 2a, the member I8 is replaced by a tapered metal cone lBa solidly joining the inner conductor 8 and the tubular outer conductor 9, as before.

In accordance with a further modified form of the invention, .support ltb (Fig. 2b) is'inthe'form of a metal com 481) similar to the cone lswbut with the taper thereof reversed.

While supports shaped like 18, Ma and |8b are particularly useful, it will be obvious that .supports of other shapes may be substituted for those shown. Since when .the rotatable portion of the assembly is being rotated each :of these supports acts as a member in tension, it keeps the rod-like conductor 8 from deflecting with respect to the tubular conductor '9, the movable portion of the antenna assembly is therefore maintained in static and dynamic balance. By properlyrelating the position of the supporting ,plug 14 and the size of the supports'suchas 18, I811 or 18?), a wide range of impedances may be matched to the coaxial line, the impedance match .being achieved for a band of frequencies. It has been :found that the supports such as .l-B, .tBa-andtbhave little effect on the antenna-pat- .tern, .since external field disturbances are not influenced. The arrangement just describeddiscloses. a marked improvement in the art sinceone element, such as 58, serves both las a-structural support as well as an impedance transformer. However, the usefulness of the supporting element l8, 180L101 i3!) is not limited to those cases in :which'the dipole assembly is rotated. When the assembly is stationary, this elementis .still of great value in providing'a means of obtaining desired impedance characteristics. The curve :A of Fig. 3:i1lustrates the wayin which thestanding wave-ratio, which is an index of impedancematch produced by a given dipole assembly, .is changed as the vdiameterof the cylindrical support is uariedzin oneparticular-antenna. I

Further, in accordance with the invention, the

antenna-assembly isprovided with aflared-hollow choke .20 attached at-its restricted end .2-! to the tubular'conductor 9. This choke which :15 essentially 1a .short-circuited coaxial line is usually resonant'at or near the operating frequency. The

character-ofthis choke :has a profoundieifect on thezantenna pattern. It will be found that etc. drequency J, the axis of the main lobe of the antenna fleldpatternin the electricaltplane will make an angle With'the mechanicalaxis of symmetry X'X of l the antenna, which-angle has been referredto as th angle of skew. Thlsaangleede pends,-to-alarge degree, on the size-.and-construction .of the choke, if-other dimensions remain-unchanged. If a certain angle of skew .is obtained at-a frequenc J for which aconventionalcylindricalechoke-is resonant, then variations intrequency about f will cause changes in .the,angl.e. It is generally desirable to keep the mentioned angle unchanged for a band .ofirequencies and the. flared choke 26 of the present .inventiomkeeps the .angle constant'overa greater range of :frequencies than the conventional choke of the prior art. Thedotted line graphBof the Chart OfI-Fig-B illustrates the .variation with frequency .in the angle of skew of one particular antenna when a conventional choke of the prior art is used, whereas, the-full line graphC of Fig. .showsiasimilar relation in the case of the flared \chokeiof the present invention used in connection with the same .antenna whereby .it will be observed that this angle remains constant over a much wider range of frequencies. While the choke 20, tapered in the manner shown in Fig. 4, was used in the particular application cited, this tapered choke 5 may have a wide variety of other flaring shapes,

as shown, for example, at 20a, 20b and 200 in Figs. 4a, 4b and 40 respectively.

Since it may lead toabetter-understanding of the invention if :an example of the relative sizes of certain component parts are known, certain dimensions in terms of wave length (A) are in- .dicated in the drawings. It will be understood, however, that these dimensions are to be conqsideredcmemly :as :illustrative of the dimensions 1 5 -usediinnnerparticular antenna and not as limiting the scopeofthis invention.

It isnot essential that the flared choke and the metal supporting element l8, be used together. Regardless of whether a cylindrical or 20 flared choke is used or whether any choke is .used, the metal supporting-element 418 :is a novel and useful device for matching impedance rand for supporting the inner conductorB. Likewise, the use of-a flared choke 20 is -a:novel-and'useul .means of producing a relatively constant .zangle of skew of the antenna beam whether ;or-not the metal supporting element A 8 is :used. In the particular antenna herein described, :both z-features were incorporated. The metal supporting '30 element is described, shown, and claimed inxmy .copending application :Serial No. 98,863, filed September '20, 1946, and assigned to :the same :assigneeas the;present invention.

Whatl claim is:

. 1. In a a dipole :antenna assembly, a coaxial lline comprising a tubular conductor .and :a central conductor mounted in. spacedgrelation'within said tubular conductor, .a conducting (dipole imember attached to-said tubular conductor :near :oneend thereof, a second conducting dipole :memb'er iattached to said central .conductorrin the region .of said first mentioned :dipole member, :and a flaring tubular choke conductlvely joined at lits restricted end etc-theoutersurface-of said tubular conductor in concentric relation thereto between the other end of saidtubular conduotorqandsaid dipole members, said choke {flaring toward :said dipole members.

.2. 3111 Pa ,dip ole antenna --assembly, '18, parabolic reflector of conducting material, a coaxial mounted :to project from said reflector :along rits axis of symmetry, said linecomprls'ingia tubular conductor and a central gconductormounted in spacedrelation within said tubular conductor, :a conducting dipole member attached :to the inrojecting end portion oil-said tubular iconductor, :9. second conducting dipolememherrattacheditosaid central-conductor in the region ofisaidfflrst :mentioned dipole member, said dipole :members :extending (away from each father, :and 2a fflar n tubular .choke conductively joined to :the outer surface -of :said tubular conductor rin concentric relation thereto adjacent said rdipole members, said choke .flaring towardsaiddipolermembers.

3. :In a dipole antenna assembly, :a ipara'bolic reflector -.of conducting material -,provi'ded with :a hollow :supportlextending rralong its axis of Sy metry, :a coaxial.-line.=mounted inis aidrsupportzantl projectingfrom .said "reflector, :said dine LGOmPI iS! ingajtubular conductor :and a central iconductor mounted in spaced relation within :said tubular conductor, a conducting dipole memher'attached to the projecting .end; portion tof said tubular 26011" ductor, :a :second conducting 'dipole :member eattached to :said central conductor, :sald =izlipole members being in substantial alignment, and a hollow choke, a part of which is cylindrical and the remainder of which flares outward, said choke being conductively joined at its restricted end to the outer surface of said tubular conductor in concentric relation thereto between said reflector and said dipole members, said choke flaring toward said dipole members.

4. In a dipole antenna assembly, a coaxial line comprising a tubular conductor and a central conductor mounted in spaced relation within said tubular conductor, said conductors being conductively joined together at one pair of their adjacent ends by a metal plug, a conducting dipole member attached to an end portion of said tubular conductor and projecting therefrom, a second conducting dipole member attached to said central conductor and projecting therefrom in the region of the first mentioned dipole member and a hollow flaring choke concentrically surrounding said tubular conductor and flaring toward said dipole members, said choke being conductively joined at its restricted end to said tubular conductor between the other end of said tubularconductor and said dipole members.

HAROLD GOLDBERG.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PAI'ENIS Number Name Date 1,927,393 Darbord Sept. 19, 1933 2,239,724 Lindenblad Apr. 29, 1941 2,274,389 Von Baeyer et al. Feb. 24, 1942 2,275,646 Peterson Mar. 10, 1942 2,287,220 Alford June 23, 1942 2,368,663 Kandoian Feb. 6, 1945 2,370,053 7 Lindenblad Feb. 20, 1945 2,407,057 Carter Sept. 3, 1946 2,412,867 Briggs et a1 Dec. 17, 1946

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