US2491493A - Dipole antenna - Google Patents

Description

-Dec. 20, 1949 H. GOLDBERG DIPOLE ANTENNA Original Filed Feb. '7, 1944- a Shejfs-Sheet 1 1N VEN TOR. HAROLD G01 D5596 ATTORNEY H. GOLDBERG DIPOLE ANTENNA Dec( 20, 1949 3 Sheets-Sheet 2 FIG. 2

Original Filed Feb. 7, 1944 FIG. 20.

FIG. 2b

. INVENTOR. HAROLD GOLDBERG A TTORWE) H. GOLDBERG,

DIPOLE ANTENNA Dec. 20, 1949 '3 Sheets-$heet 5 Original Filed Feb. 7, 1944 000A (102A 004% 0.0% 0.081 OJOX DIAMETER OF SUPPORT l8 Has FIG 4 b FIG. 4c

mwwm uwa 2535 m0 m OZ FREQUENCY IN V EN TOR. HA 1901 D GOLDBERG ATTORN Patented Dec. 20, 1949 DIPOLE ANTENNA Harold Goldberg, Baltimore, Md., assignor to Stromherg-arlson Company, Rochester, N. Y., a corporation of New York @riginal application February '7, 1944, Serial No.

521,4:56. Divided and this application September 20, 1946, Serial No. 698,363

'7 Claims. (01. 250-33.65)

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

ihis is a division of my copending application Serial No. 521/256, filed February 7, 1944, now Patent 2/i78,913 issued August 16, 1949, and assigned to the same assignee as the present invention.

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. Phis 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 projects at right angles to each conductor with i .ld members extending in alignment in opposite direct-ions therefrom. In some instances, this diassembly is rotated at relatively high speed about the mentioned axis of symmetry with the result that there are set up, centrifugal forces which tend to the inner conductor thereof render the operation of the antenna unsatisfactory. While dielectric supports have been suggested for maintaining a fixed special relationship between the coaxial conductors, supports of such material have been generally unsatisfactory. The use of metal supports, on the other hand, has not been indicated, since metal would short circuit these conductors and it was therefore believed that the antenna assembly wou d be rendered inoperative. It has been discovered, however, that a r etal support of suitable dimensions when joined to the mentioned coaxial conductors in the proper location thereetween, not only effects static and dynamic balancing thereof but improves the electrical charcteristics or" 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 01 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 tie of shew. This angle has former- 1y 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 pair, being in effect a short circuited coaxial line. It has 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,

2 reference is made to the following description and claims when taken with the drawingsin which:

Fig. is a vertical longitudinal section 01": the dipole antenna assembly of the present invention;

Figs. 2, 2a and 2b are enlarged sectional views of varied forms of a support mounted at the junction o the respective dipole members with their respective conductors;

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 the cylindrical type of support is varied;

Fig. 4 is an enlarged perspective View of the choke of Fig. l; and Figs. 4a, 4b and lo 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 a uminum or similar light metal reflector, the 1' surface of which conforms to a paraboloid of revolution. This reflector has a central hollow support i.- extending along its axis of symmetry X-X. Through this support, there ex tend the rigid coaxial conductors 8 and 9. These conductors of which conductor 8 is a central rod or tube and the conductor 9 a tube, are uniformly spaced from each other to serve as a socalled coaxial line. This coaxial line which thus projects along the axis of symmetry X-X of the reflector is mounted on suitable bearing iii in sup port to be rotated by motor M around this axis. The end portion of the tube 9 has a conducting rod-like dipole member i! joined to the exterior thereof and extending at right angles thereto. Similarly, the rod it has a second dipole mem her it joined thereto to project through an opening id 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 is mounted thereon in parallel relation to the dipole members. The rotatable portion of the coaxial line, comprising the inner conductor 8 and the other conductor 9', is capacitively coupled by the sleeves l6 and ll to a fixed portion of a coaxial line comprising the rod or tube Ba and the tubular conductor 9a, which extends at right angles to axis XX.

In accordance with this invention, the inner 3 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 8, 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 68a solidly joining the inner conductor 3 and the tubular outer conductor 9, as before.

In accordance with a further modified form oi the invention, support is?) (Fig. 2b) is in the form of a metal cone liib similar to the cone lfia but with the taper thereof reversed.

While supports, shaped like 58, 58a and 1811 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 properly relating the position of the supporting plug l t and the size of the supports such as i8, I811 or i819, 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 l8, its and 5812 have little effect on the antenna pattern, since external field disturbances are not influenced. The arrangement just described discloses a marked improvement in the art since one element, such as 68, serves both as a structural support and as an impedance transformer. However, the usefulness of the supporting element i8, i8a or 5811 is not limited to those cases in which the dipole assembly is rotated. When the assembly is stationary, this element is still of great value in providing a means of obtaining desired impedance characteristics The curve A of Fig. 3 illus trates the way in which the standing Wave ratio, which is an index of impedance match produced by a given dipole assembly, is changed as the diameter of the cylindrical support 93 is varied in one particular antenna.

Further, in accordance with the invention, the antenna assembl is provided with a flared hollow choke 26 attached at its restricted end 2i to the tubular conductor 9. This choke which is essentially a sl'lort-circuited coaxial line is usually resonant at or near the operating frequency. The character of this choke has a profound efiect on the antenna pattern. It will be found that a frequency f, the axis of the main lobe of the antena field pattern in the e ectrical plane will make an angle with the mechanical axis of sym metry XX of the antenna, which angle has been referred to as the angle of skew. This angle depends, to a large degree, on the size and construction of the choke, if other dimensions remain unchanged. If a certain angle of skew is obtained at a frequency f for which a conventional cylindrical choke is resonant, then variations in frequency about f will cause changes in the angle. It is generally desirabie to keep the mentioned angle unchanged for a band of frequencies and the flared choke 2d of the present invention keeps the angle constant over a greater range of frequencies than the conventional choke of the prior art. The dotted line graph B of the chart of Fig. illustrates the vari ation 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 graph C of Fig. 5 shows a similar relation in the case of the flared choke of 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 2B, tapered in the manner shown in Fig. i, was used in the particular application cited, this tapered choke may have a wide variety of other flaring shapes, as shown, for example, at 28a, 26?) and 290 in Figs. 4a, 4b and sic respectively.

Since it may lead to a better understanding of the invention if an example of the relative sizes of certain component parts are known, certain dimensions in terms of wave length (x) are indicated in the drawing. It will be understood, however, that these dimensions are to be considered merely as illustrative of the dimensions used in one particular antenna and not as limiting the scope of this invention.

It is not essential that the two novel features of this invention, namely the flared choke 20 and the metal supporting element l8, be used together. Regardless of Whether a cylindrical or flared choke is used or whether any choke is used, the metal supporting element 68 is a novel and useful device for matching impedance and for supporting the inner conductor 8. Likewise, the use of a flared choke 2b is a novel and useful means of producing a relatively constant angle of skew of the antenna beam whether or not the metal supporting element i8 is used. In the particular antenna herein described, both features were incorporated.

What I claim is:

1. In a dipole antenna assembly, a coaxial line comprising a tubular conductor and a central conductor mounted in spaced relation within said tubular conductor, 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 in the region of said first dipole member and projecting therefrom through an opening in said tubular conductor, and a conducting metal piece directly joining said conductors at said dipole members.

2. In a dipole antenna assembly, a parabolic reflector of conducting material, a coaxial line mounted to project from said reflector alon its axis of symmetry, said line comprising a tubular conductor and a central conductor mounted in spaced relation within said tubular conductor, a conducting dipole member attached to the projecting end portion of said tubular conductor and extending at an angle thereto, a second conducting dipole member attached to said central conductor and projecting at an angle thereto through an opening in said tubular conductor, said dipole members extending away from each other, and a metal piece directly and conductively joining said conductors at said dipole members, said metal piece having a cross section less than that of at least one of said dipole members.

3. In a dipole antenna assembly, a parabolic reflector of conducting material provided with a hollow support extending along its axis of symmetry, a coaxial line rotatable in said support and projecting from said reflector, said line comprising a tubular conductor and central conductor mounted in spaced relation within said tubular conductor, a conducting dipole member attached to the projecting end portion of said tubular conductor and extending at right angles thereto, a

second conducting dipole member attached to said central conductor and extending at right angles thereto through an opening in said tubular conductor, said dipole members being in substantial alignment, and a cylindrical metal piece directly and conductively joining said conductors at said dipole members.

4. In a dipole antenna assembly, a parabolic reflector of conducting material provided with a hollow support extending along its axis of symmetry, a coaxial line mounted in said support and projecting from said reflector, said line comprising a tubular conductor and a central conductor mounted in spaced relation within said tubular conductor, a conducting dipole member attached to the projecting end portion of said tubular conductor and extending at right angles thereto, a second conducting dipole member attached to said central conductor and extending at right angles thereto through an opening in said tubular conductor, said dipole members being in substantial alignment, and a metal piece having the shape of a truncated cone and conductively joining said conductors at said dipole members.

5. In a dipole antenna assembly, a parabolic reflector of conducting material provided with a hollow support extending along its axis of symmetry, a coaxial line rotatable in said support and projecting from said reflector, said line comprising a tubular conductor and a central conductor mounted in spaced relation within said tubular conductor, a conducting dipole member attached to the projecting end portion of said tubular conductor and extending at right angles Ir thereto, a second conducting dipole member attached to said central conductor and extending at right angles thereto through an opening in said tubular conductor, said dipole members being in substantial alignment, and a metal piece having a cross section less than that of one of said dipole members, said piece directly and conductively joining said conductors at said dipole members.

6. In a dipole antenna assembly, a coaxial line comprising a tubular conductor and a central conductor mounted in spaced relation within said tubular conductor, 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 in the region of said first dipole memher and projecting therefrom through an opening in said tubular conductor, and a conducting metal piece directly joining said conductors at said dipole members, said metal piece being disposed entirely within said tubular conductor.

7. In a dipole antenna assembly, a parabolic reflector of conducting material, a coaxial line mounted to project from said reflector along its axis of symmetry, said line comprising a tubular conductor and a central conductor mounted in spaced relation within said tubular conductor, a conducting dipole member attached to the projecting end portion of said tubular conductor and extending at an angle thereto, a second conducting dipole member attached to said central conductor and projecting at an angle thereto through an opening in said tubular conductor, said dipole members extending away from each other, and a metal piece directly and conductively joining said conductors at said dipole members, said metal piece being disposed entirely within said tubular structure and having a cross section less than that of at least one of said dipole members.

HAROLD GOLDBERG.

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

UNITED STATES PATENTS Number Name Date 2,175,363 Van Roberts Oct. 10, 1939 2,243,426 Kircher May 27, 1941 2,275,030 Epstein Mar. 3, 1942 2,275,646 Peterson Mar.. 10, 1942 2,298,449 Bailey Oct. 13, 1942 2,412,867 Briggs et al Dec. 17, 1946 2,417,895 Wheeler Mar. 25, 1947 2,446,436 Rouault Aug. 3, 1948

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