US2935747A

US2935747A - Broadband antenna system

Info

Publication number: US2935747A
Application number: US569565A
Authority: US
Inventors: Rabindra N Ghose
Original assignee: RCA Corp
Current assignee: RCA Corp
Priority date: 1956-03-05
Filing date: 1956-03-05
Publication date: 1960-05-03
Anticipated expiration: 1977-05-03

Description

y 3, 1960 R. N. GHOSE 2,935,747

BROADBAND ANTENNA SYSTEM Filed March 5, 1956 2 Sheets-Sheet 2 INVENTQR. RAB/NORA N. 5/4055 1 .10. 25441 M WM Irma 5r BROADBAND ANTENNA SYSTEM Rabindra N. Ghose, Philadelphia, 'Pa., assignor to Radio Corporation of America, a corporation of Delaware Application March '5, 1956, Serial No. 569,565

17 Claims. (Cl. 343-767) This invention relates to broadband antennas useful without change over a very broad frequency range.

The physical dimensions of an antenna are selected in terms of the wavelength of the signal at the center of the desired operating frequency band. A feed line is connected to the antenna in such a manner as to provide an impedance match at the operating frequency. As the signal frequency departs from the center frequency for which. the antenna is designed, the impedance presented by the antenna to the feed line changes from a matched value to an increasingly unmatched value with the result that the antenna is increasingly ineffective or inefi'icient. Some antennas are effective over wider frequency bands than others. For example, a how-tie dipole or a conical dipole is less frequency sensitive than asimple linear dipole. 1

,It is an object of this invention to provide an improved antenna system useful over a broader frequency range than that of previously known antennas.

It is another object to provide a novel antenna um comprising a parallel combination of a bow-tie dipole in parallel with a bow-tie slot antenna.

It is a further object to provide novel arrays of antenna units each including a bow-tie dipole in parallel with a bow-tie slot.

In one aspect, the invention comprises an antenna unit consisting of a bow-tie dipole made of two generally triangular conductive sheets arranged in mirror image fashion about an axis with adjacent corners in closely spaced relation to provide a two-terminal feedpoint, and with conductive elements or bars connecting corresponding distant corners of the sheets to define a bow-tie slot States atent between the sides of the dipole sheets and the conductive elements. A plurality of antenna units may be arranged in a layer to provide an omni-directional pattern in a given plane. Also, a plurality of antenna units or layers of units may be arranged in a linear array to provide a pattern of increased directivity in planes passing thru the axis of the linear array.

These and other objects and aspects of the invention will be apparent to those skilled in the art from the following more detailed description taken in conjunction with the appended drawings, wherein:

Figure 1 is an elevation of an antenna unit according to the invention and including a bow-tie dipole in parallel with a bow-tie slot;

Figure 2 is an isometric view of a plurality of antenna units according to Figure 1 arranged in a layer to provide an omni-directional pattern in the horizontal plane;

Figure 3 is an isometric view of an antenna similar to that of Figure 2 but arranged for vertically polarized waves rather than horizontally polarized waves;

Figure 4 is an elevation of a linear array of antenna units as shown in Figure 1, or layers of antenna units as shown in Figure 2;

Figure 5 is a transverse sectional view illustrating a method of feeding the layer of antenna units shown in Figure2;.

2,935,747 Patented May 3, 1960 Figure 6 is an elevation of an antenna system including a plurality of layers of antenna units according to Figure 2 with a common feed system including a hollow pipe waveguide;

Figure 7 is a transverse section taken on the line 77 of Figure 6;

Figure 8 is an elevation of an antenna unit differing from that of Figure l in that the bow-tie slot is of exponential configuration;

Figure 9 is an elevation of an antenna unit difiering from that of Figure 1 in that the bow-tie slot is of hyperbolic configuration; and

Figure 10 is an elevation of an antenna unit diifering from that of Figure 1 in that the bow-tie slot has a Dolph- Tchebyschefi configuration.

Figure 1 shows an antenna unit including a bow-tie dipole in parallel with a bow-tie slot. The bow-tie dipole includes two generally triangular

conductive sheets

12 and 13 arranged in mirror-image fashion about an axis 14 with adjacent corners 15 and 16 in closely spaced relation to provide a two-terminal feedpoint for a feed line 17. Rod-like relatively narrow conductive elements or

bars

18 and 19 connect the corresponding

distant corners

20 and 21, and 2 2 and 23, respectively, of the

conductive sheets

12 and 13. The

conductive elements

18 and 19 cooperate'with the edges of the

conductive sheets

12 and 13 to define a bow-tie slot having sub-. stantially the same size as the bow-tie dipole and comprising two triangular open spaces 8 and 9. The bowtie'dipole '12, 13' and the bow-tie slot have a common feedpoint 15, 16 and are electrically in parallel. Figure 1 is an elevation of an antenna unit arranged for transmitting or receiving horizontally polarized waves. Stated another way, the polarization of the radio frequency energy is orthogonally related to the axis 14. The con

ductive sheets

12 and 13 may be constructed of sheet metal, or may, of course, be constructed of a grid or other lattice of conductive elements sufi'iciently closely spaced to effectively provide a current sheet at the operating frequencies.

The impedance characteristics of a bow-tie dipole and a bow-tie slot of the same size are complementary. That is, if the dipole is inductive, the slot is capacitive, and vice versa. The slot of a slot antenna is normally of small size compared with the conductive sheet from which the slot is cut. However, it has been found, according to this invention, that a bow-tie dipole and a bow-tie slot can be constructed electrically in parallel to utilize the complementary impedance characteristics of the dipole and the slot for the purpose of providing an antenna unit useful over a very broad range of frequencies.

Figure 2 shows four antenna units of the type shown in Figure 1 arranged in planes forming the walls of a prism to constitute a layer of units providing a substantially omni-directional pattern in the horizontal plane. While four units have been shown in the layer, a smaller or larger number of units may be employed. The adjacent edges 27 of the antenna units may be connected together but are preferably mounted in insulated spaced relationship by means of insulating blocks 28 as shown in the drawings. Each pair of spaced adjacent edges 27 define the opposite edges of a slot antenna which improves the circularity of the pattern of the layer of units. The layer of antenna units arranged according to Figure 2 is useful for transmitting or receiving horizontally polarized waves, and the antenna provides a substantially omnidirectional pattern in the horizontal plane. Figurc3 shows a layer of antenna units each accord? ing to Figure 1 and similar to the layer shown in Figure 2 except that the antenna units are turned degrees compared to those of Fig. 2. The arrangement shown in Figure 3 is useful for transmitting or receiving vertically polarized waves, and the arrangement provides a substantially omni-directional pattern in the horizontal plane. It will be noted that in. Figure 3 each bow-tie dipole has a fmirror axis extending in the horizontal direction, whereas. in Figure 2, each dipole has a mirror axis extending in a vertical direction.

Figure 4 illustrates a linear or vertical array of. antenna units each according to Figure 1. It will be noted that the feedpoints 15', 16' to which the transmission line is connected are displaced downwardly from the horizontal axis of each antenna unit. This results in a downward tilting of thebeam'and maybe desirable to minimize the amount of energy directed above the hori- Zen and ordinarily wasted. Layers of antenna elements as shown in Figure 2 may also be arranged in a linear array in a manner analogous to that illustrated in Figure 4.

Figure is a transverse sectional view illustrating a method of feeding a layer of antenna units as shown in Figure 2. A central coaxial feed line includes an inner conductor 30 and an outer conductor 31. The

coaxial line

30, 31 terminates centrally within the structure shown in Figure 2. Parallel wire

lines including conductors

32 and 33 connect the inner and

outer conductors

30, 31 to the feedpoints 15, 16 of each bow-

tie dipole

12, 13.

An antenna layer according to Figure 2 was constructed with a feed system according to Figure 5. The antenna layer was of cubic configuration with all sides equal to 15 inches. The

coaxial line

30, 31 had a charaoteristic impedance of 75 ohms. The

parallel conductor lines

32, 33 had a characteristic impedance of 300 ohms. The experimental antenna thus constructed was found to have a frequency range of from 330 to 1880 megacycles with a standing wave ratio of less than 2. The antenna pattern in the horizontal plane varied from perfect circularity by 2 decibels.

Figure 6 shows a linear array of layers, each like that of Figure 2, the array being fed by a hollow pipe waveguide 40. Each dipole and slot unit is fed from the hollow pipe waveguide 40 by means of a coaxial line having an outer conductor 41 connected to one side of the dipole, and an inner conductor 42 connected at one end to the other side of the dipole and at the other end extending into the hollow pipe waveguide '40 as a probe for picking up energy therein. The details of the construction are illustrated in the cross-sectional view of Figure 7.

' Energy is fed in at the lower end of the hollow pipe waveguide 40 by means of a coaxial line including an outer conductor 43 connected to the walls of the hollow pipe waveguide 40, and an inner conductor 44 extending into the interior of the wavegmide 40 to act as a probe. Fins 45 may be inserted in the waveguide 40 to cause a rotation of the polarization of the radio frequency energy traveling up the waveguide. Any reflected energy traveling back down the waveguide 40 is again rotated when it passes by the fins 45. The polarization rotating fins 45 are designed to cause a 45 degree rotation of the polarization each time the wave passes by the fins. Therefore, reflected energy is rotated a total of 90 degrees and is coupled to a coaxial line 46 which is connected at the other end to an absorbing or dissipating resistor (not shown). It will be noted that the coaxial linev 46 is orthogonally related to'the input

coaxial line

43, 44. In this way, reflected energy is prevented from coupling thru the input

coaxial line

43, 44 to the source (not shown). The various layers of antennas are spaced vertically along the waveguide 40 at points such that all the antenna units are fed in phase.

Figures 8 thru show variations in the configurations of the bow-tie dipole and complementary bow-tie slot. These arrangements are useful for providing a smooth impedance transformation from the feed line to free space (377 ohms) when the physical size of the antenna unit is restricted or predetermined by practical considerations. Figure 8 shows an antenna unit with an exponential slot; Figure 9 shows one with a hyperbolic slot; and Figure 10 shows one with a Dolph-Tchebyschetr slot. In all cases, the bow-tie antenna and the associated slot antenna are of substantially the same size, and the bow-tie antenna consists of two generally triangular conductive sheets.

The antenna unit of this invention includes a current sheet antenna in parallel with a voltage sheet antenna. The bow-tie dipole constituted by the

conductive sheets

12 and 13 is a current sheet antenna. The bow-tie slot defined by the edges of the

conductive sheets

12 and 13, and the conductive elements or

bars

18 and 19 is a voltage sheet antenna. The feedpoints 15 and 16 provide for operation of the two antennas in parallel. The impedance characteristics of the two antennas are substantially complementary, that is, the impedances of the two antennas vary with frequency in such a way that the impedance of both antennas in parallel remains substantially constant over a very wide frequency range.

The term bow-tie dipole, sometimes referred to as a fan dipole, is deemed to comprise a pair of radiating elements arranged end-to-end and spaced from one another at adjacent ends, each radiating element being a conductive sheet of very generally triangular configuration having a narrow or apex portion located adjacent the narrow or apex portion of the other radiating element from which it is spaced. The term bow-tie slot has a similar meaning except that it is considered to comprise very generally a triangular space or opening as contrasted to the triangular conductive sheets.

What is claimed is:

1. A broadband antenna unit comprising, a bow-tie dipole including two generally triangular conductive sheets arranged in mirror image fashion about an axis with adjacent corners in closely spaced relation to provide a two-terminal feedpoint, and rod-like conductive elements connecting corresponding distant corners of said sheets to define a bow-tie slot between said elements and the edges of said sheets, said bow-tie slot comprising triangular-shaped spaces between the rod-like elements and the sides of the triangular sheets.

2. A broadband antenna unit comprising, a bow-tie dipole including two generally triangular conductive sheets arranged in mirror image fashion about an axis with adjacent corners in closely spaced relation to provide a two-terminal feedpoint, and straight rod-like conductive elements directly connecting corresponding distant corners of said sheets to define a bow-tie slot between said elements and the edges of said sheets, said bow-tie slot comprising triangular-shaped spaces between the rod-like elements and the sides of the triangular sheets, said bow-tie dipole and said bow-tie slot being of substantially the same size and having substantially complementary impedance characteristics with frequency.

3. A broadband antenna unit comprising, a bow-tie dipole including two generally triangular conductive sheets arranged in mirror image fashion about an axis with adjacent corners in closely spaced relation to provide a. two-terminal feedpoint, and a rod-like conductive element directly connecting together at least one pair of corresponding distant corners of said sheets.

4. A broadband antenna unit comprising, a bow-tie dipole including two generally triangular conductive sheets arrmged in mirror image fashion about an axis with the narrow portions adjacent to one another in closely spaced relation to provide a two-terminal feedpoint, and conductive bars directly connecting together corresponding distant corners of said sheets to define a bow-tie slot between said bars and the edges of said sheets.

-5. A linear array of a plurality of complementary antenna units each comprising a bow-tie dipole including two generally triangular conductive sheets arranged in mirror image fashion about an axis the narrow portions adjacent to one another in closely spaced relation to provide a two-terminal feedpoint, and rod-like conductive elements directly connecting together corresponding distant corners of said sheets to define a bow-tie slot between said'elements and the edges of said sheets; and feeder means connected to the feedpoints of all of said antenna units.

6. A broadband layer array of complementary antenna units, comprising, a plurality of bow-tie dipoles each including two generally triangular conductive sheets arranged in mirror image fashion about an axis the narrow portions adjacent to one another in closely spaced relation to provide a two-terminal feedpoint, means to mount said plurality of dipoles in planes forming the walls of a prism, and relatively narrow conductive elements directly connecting corresponding together distant corners of the sheets forming each dipole to define bowtie slots therebetween.

7. A broadband layer array of complementary antenna units, comprising, a plurality of bow-tie dipoles each including two generally triangular conductive sheets arranged in mirror image fashion about an axis with the narrow portions adjacent to one another in closely spaced relation to provide a two-terminal feedpoint, means to mount said plurality of dipoles in planes forming the walls of a prism, said axis of each dipole being parallel with the axis of said prism, straight, relatively narrow conductive elements directly connecting together corresponding distant corners of the sheets forming each dipole to define bow-tie slots therebetween.

8. A broadband layer array of complementary antenna units, comprising, a plurality of bow-tie dipoles each including two generally triangular conductive sheets arranged in mirror image fashion about an axis with the narrow portions adjacent to one another in closely spaced relation to provide a two-terminal feedpoint, means to mount said plurality of dipoles in planes forming the walls'of a prism, said axis of each dipole being at right angles with the axis of said prism, and straight, relatively narrow conductive elements directly connecting together corresponding distant corners of the sheets forming each dipole to define bow-tie slots therebetween.

9. A broadband antenna unit comprising, conductive elements forming a bow-tie dipole antenna and a bowtie slot antenna therebetween, said conductive elements having a configuration such that the impedance characteristics of the two antennas are substantially complementary, and feeder means coupled to said antennas for operating said two antennas in parallel.

10. An antenna as defined in claim 1 wherein the sides of the slot taper exponentially.

11. An antenna as defined in claim 1 wherein the sides of the slot taper in hyperbolic manner.

12. An antenna as defined in claim 1 wherein the slot is a Dolph-Ichebyschefi slot.

13. A broadband layer array of complementary antenna units one above the other, each unit comprising a plurality of bow-tie dipoles, each dipole including two said dipoles surrounding a portion of said mast, and rodlike conductive elementsdirectly' connecting corresponding distant comers of said sheets forming each dipole to define bow-tiev slots therebetween.

14. A broadband antenna unit comprising a bow-tie dipole including two generally triangular conductive sheets arranged in mirror image fashion about an axis with the narrow portions adjacent to one another and closely spaced to provide a two-terminal feed point, and conductive bars directly connecting together symmetrically positioned points on said sheets along a line substantially perpendicular to said axis so as to define a bow-tie slot between said bars and the edges of said sheets.

15. A broadband antenna unit comprising conductive elements forming a bow-tie dipole antenna and a bow-tie slot antenna therebetween, said slots being formed by the diverging edges of said bow-tie antenna and conductors directly connecting together correspondingly positioned corners to said bow-tie antenna, and said conductive ele ments having a configuration such that the impedance characteristics of said antennas are substantially complementary.

16. A broadband array as definedin claim 13 wherein said mast comprises a hollow conductive cylinder having openings therein along the length thereof adjacent each of said feed points, a transmission line positioned within said mast, and feed means extending through each of said openings and connected between said transmission line and each of said feed points.

17. An antenna comprising two triangular sheets of 1 conductive material in the same vertical plane, each sheet having a base and sloping sides converging from the corners of said base to an apex, the apices of said two sheets being adjacent to but spaced from each other, and straight rod-like conductive elements respectively directly connecting together the corners of said bases which are located on the same side of the apices, to thereby define triangular-shaped open spaces between the rod-like elements and the sloping sides of the sheets, whereby said sheets form a bow-tie dipole, and the spaces between the sloping sides and the conductive elements form a bow-tie slot.

References Cited in the file of this patent UNITED STATES PATENTS 2,199,635 Koch May 7, 1940 2,507,528 Kandoian May 16, 1950 2,631,237 Sichak et a1. Mar. 10, 1953 2,656,463 Woodward Oct. 20, 1953 2,660,674 Brown Nov. 24, 1953 2,665,382 Smith Jan. 5, 1954 2,820,220 Charman Jan. 14, 1958 2,827,628 Swinehart et a1. Mar. 18, 1958 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No, 2,935,747 May 3, 1960 Rabindra N. Ghose It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column l, line 36 for "in parallel with"v read antenna and column 5, line 58 for Iehebyscheff read Tchebyscheff Signed and sealed this 6th day of December 1960,

(SEAL) Attest:

KARL H. AXLINE ROBERT C. WATSUN Attesting Oflicer Commissioner of Patents