US2732551A

US2732551A - Spherical cage antenna

Info

Publication number: US2732551A
Authority: US
Publication date: 1956-01-24
Anticipated expiration: 1973-01-24

Description

Jan. 234, 1956 J. D. KRAUS 5 SPHERICAL. CAGE ANTENNA Filed March 24, 1954 i 32 INVENTOR. 0 John D. Kraus ATTORNEYS.

2,732,551 SPHERICAL CAGE ANTENNA John D. Kraus, Columbus, Ohio, assignor, by mesne assignments, to The Battelle Development Corporation,

Columbus, Ohio, a corporation of Delaware Application March 24, 1954, Serial No. 418,312

9Claims. ci.343-s4s This invention relates to antennas. It has to do, more particularly, with a spherical cage antenna comprising a plurality of wire loops'positioned at equal angles about a common axis.

A primary object of the invention is to provide an antenna having a maximum dimension of approximately one-quarter wave length at the operating frequency and providing gain over a monopole antenna one-quarter wave long at' the operating frequency.

Another object of the invention is to provide an antenna that can be used over a wide frequency band.

- A further object is to provide an antenna having an omnidirectional radiation pattern in the horizontal plane, with maximum radiation in the horizontal plane, decreasing radiation withincreasing angle above or below the horizontal plane, and substantially zero radiation vertically.

It is also an object of this invention to provide an antenna that is useful for high-frequency, wide-band applications.

Other objects and advantages of the invention will be apparent from the disclosure herein.

' A preferred form of antenna according to the present invention comprises a spherical ball or cage made up of a plurality of vertical Wire loops positioned at equal angles around a common vertical axis. These loops are circular and are arranged like the lines of equal longitude on a globe. The antenna is energized through a coaxial cable with the outer conductor connected to alternate loops at the lower end of the common'vertical axis and with the inner conductor connected to the lower end of a vertical monopole positioned along the vertical axis of the sphere, the monopole being connected at its upper end to the alternate loops other than those that are connected to the outer conductor at the lower end of the axis. The diameter of the antenna is approximately one-quarter wave length at the operating frequency. Although it has only one half the maximum dimension of a half wave vertical antenna, the antenna of this invention provides a radiation pattern approximating that of a half-wave verti cal dipole antenna. The gain is between 1 db and 2 db over a quarter-wave monopole. The antenna operates with voltage standing wave ratios not greater than 2 to 1 over a band Width of four per cent, and with a conventional impedance matching network this band width could be increased to ten per cent. The antenna has an omnidirectional radiation pattern in the horizontal plane with maximum radiation in the horizontal plane, decreasing radiation with increasing angle above or below the horizontal, and substantially zero radiation in the vertical direction.

In the drawings:

Fig. 1 is aperspective view showing a preferred embodiment of an antenna according to the present invention; 1 4

Fig. 2 is a top'view, partially antenna of Fig. 1;

conventionalized, of the Fig. '3 is a simplified schematic perspective'view illus- 2,732,551 iateniged Jan. 24, 2' A 1 connecting the loops of the antrating one manner of tenna;

Fig. 4 is a simplified schematic perspective view illus: trating an alternative manner of connecting the loops of the antenna; and

Fig. 5 is a graph in polar coordinates showing the approximate vertical radiation power pattern of an antenna according to the present invention.

Referring to Fig. 1, an antenna according to the present invention is indicated generallyby the reference numeral 10.. In the antenna 10, a monopole 11 made of copper or other good conducting metal is connected at its lower end 12 to the inner conductor 13 of a coaxial cable transmission line 14. The upper end 15 of themonopole 11 is connected to a group of alternate circular loop conductors 16-16 made of copper or other good conducting metal. The loops 16-16 have equal diameters and are disposed with a diameter of each loop 16 substantially coinciding with the monopole 11 and with the planes of theloops 16-16 disposed at equal angles around the common diameter. The outer conductor 17 of the coaxial cable 14 is connected at its upper end 18 to another group of alternate circular loop conductors 19-19 made of copper or other good conducting metal. The loops 19-19 have the same diameter as the loops 16-16 and are similarly disposed midway between the planes of the loops 16-16. The group of alternate loops 16-16, which is connected to the upper end of the monopole 11, isinsulated from the group of loops 19-19 connected to the outer conductor 17 of the coaxial cable 14.

Fig. 2, which is a partially conventionalized view of the antenna of Fig. 1 showing only the top part of the antenna 10, clearly shows that the loops 16-16 do not contact the loops 19-19 at the top of the antenna 10, as the ends of the l0ops'19-19 do not contact any of the other loops, while the loops 16-16 are connected together at the top end 15 of the monopole 11. At the bottom of the antenna the appearance is similar, with the loops 19-19 connected together and with the ends of the loops 16-16 spaced from the other loops. Thus the loops 16-16 are insulated from the loops 19-19 by spacing at all parts of the antenna 10. The length of the monopole 11 and the diameter of the loops 16-16 and 19-19 are approximately one-quarter wave length at the operating frequency.

Fig. 3, which is a schematic perspective view, simplified to include only two loops, shows that the loop 16 is connected to the top end 15 of the monopole 11, while the bottom ends of the loop 16 are spaced from the other parts of the antenna as is indicated at 20-20. The loop 19 is connected to the end 18 of the outer conductor 17 of the coaxial cable 14, while the upper ends of the loop 19 arespaced fromthe "remainder of the antenna 10 as is'indicated at 21-21. The arrowhead 22 pointing upward in the monopole 11 and the arrowheads 23-23 pointing downward in the

loops

16 and 19 indicate the direction of the currents in the antenna 10 at a given instant and illustrate the fact that the currents in the loops are in phase and that the current in the monopole is out of phase with the currents in the loops. With a larger number of loops, as the six shown inthe antenna of Figs. 1 and 2, all of the currents are out and down from the top in the loops 16-16 and 19-19 at a given instant, as is illustrated by the arrows 23-23 inFig. 2. At the same instant, the current in the monopole is up.

An alternative construction is shown in Fig. 4, which is identical to Fig. 3 except that the bottom ends of the loop 16 are connected together as is indicated at 24 and the top ends of the loop 19 are connected together as is indi catedat 25.' The loop 16 is insulated from all otherparts of the antenna 10 except at the top end15 Where it is connected to the monopolpe 11. The loop 19 is insulated from all other parts of the antenna except at the end'18 of the outer conductor 17 of the coaxial cable 14 to which the loop 19 is connected. If additional loops are included, all of the group of loops 1616 can be connected together at the lower end 24 as well as at the upper end 15, and all of the other group of loops 19-49 can be connected together at the upper end 25 as well as at the lower end 18. The currents in the closed-loop form of the antenna 10, as illustrated in Fig. 4, are the same as in the open-loop form of the antenna shown in the other figures. When the current is up, as is indicated by the arrowhead 22, in the monopole 11 of Fig. 4, the currents in the

loops

16 and 19 are down, as is indicated by the arrowheads 2323.

When the current is down in the monopole 11 in either the open-loop form or the closed-loop form of the antenna 10, the currents in the loops 1616 and 19-19 are up. The currents in the loops 1616 and l919 are substantially in phase, while the current in the monopole 11 is substantially 180 degrees out of phase with the currents in the loops 16-16 and 19-19.

' The pattern of the antenna having only two loops, as in Figs. 3 and 4, is approximately omnidirectional in the horizontal plane. To provide a more nearly uniform horizontal pattern, however, four loops can be used, consisting of two loops 16-16 connected to the top 15 of the monopole 11 and two loops 1919 connected to the end 18 of the outer conductor 17 of the coaxial cable 14. Six loops or even more can be used if desired, but

there is no electrical advantage to more than six such as shown in Figs. 1 and 2.

The horizontal radiation pattern of the six-loop antenna of Figs. 1 and 2 is a circle. The vertical radiation pattern of the antenna is as suggested in Fig. 5. An edge view of the horizontal plane is indicated at H. The line V is a vertical line, and the graph is the vertical radiation pattern of the antennas of Figs. 1-4 with the monopole 11 positioned vertically. The graph 30 shows the approximate relative power radiation at all vertical angles, the radiation at any angle being proportional to the distance from the origin 0 to the point on the graph or pattern 30 at the given angle. The relative radiation at the angle A is represented by the length of the broken line segment 31. It is apparent that maximum radiation is obtained in the horizontal direction as is indicated by the

horizontal segments

32 and 33 which are longer than any straight-line segment that can be drawn from the origin 0 to any other point on the pattern 36. It is apparent from the pattern 30 that radiation vertically is zero, since the pattern 30 coincides with the origin 0 at angles of degrees above and below the horizontal plane H as represented by the vertical line V. The pattern 30 is symmetrical, of course, about the vertical axis V, since the antenna 10 is symmetrical about its vertical axis, along which the monopole 11 is located.

For most purposes, it is desirable to have maximum radiation in the horizontal plane, but the antenna may, of course, be set with the monopole 11 in a direction other than vertical if it is desired to aim the maximum radiation of the antenna away from the horizontal.

While the operation of the antenna has been discussed herein primarily in connection with radiation from the antenna, it is apparent from the principle of reciprocity that the pattern and impedance characteristics of the antenna are the same both in transmitting and in receiving.

To summarize, the antenna of the present invention comprises a plurality of conductors, each formed in a substantially circular loop, the loops having equal diameters and being disposed with a diameter of each loop substantially coinciding with a diameter of each of the other loops and with the planes of the loops disposed around the common diameter at equal angles to the planes of adjacent loops. Alternate loops, forming a first group, are connected'together at one endof the common diameter, and the other alternate loops, forming a second group, are connected together at the opposite end of the common diameter. The outer conductor of a coaxial cable is connected to the common connection of the first group of alternate loops and the inner conductor of the coaxial cable is connected to one end of a monopole extending along the common diameter of the loops and connected at its opposite end to the common connection of the second group of loops. The diameter of each loop preferably is approximately one-quarter wave length at the operating frequency. At this frequency, the current in each loop is substantially in phase with the current in each of the other loops, and the current in the monopole is substantially degrees out of phase with the currents in the loops. With the monopole vertically positioned, the antenna provides substantially uniform radiation and reception in any horizontal direction, maximum radiation and reception in the horizontal plane, decreasing radiation and reception with increasing angle above or below the horizontal plane, and substantially zero radiation and reception in the vertical direction. The loops of the first group are insulated from the loops of the second group, and each loop may be a continuous circular member or may be open at the end of the common diameter opposite the end at which the loop is connected to the other loops of the same group. The antenna has a radiation pattern approximating that of a half-wave dipole, and provides a gain of between 1 db and 2 db over a quarter-wave monopole. Voltage standing wave ratios not greater than 2 to 1 are obtained over a four per cent band, and a conventional impedance matching network can be used to increase the band width to 10 per cent for a maximum voltage standing wave ratio of 2 to 1.

From the foregoing disclosure, it is apparent that the present invention provides an antenna that is useful for high-frequency wide-band applications, the antenna having a maximum dimension of approximately one-quarter wave length at the operating frequency and providing gain over a monopole antenna having a length equal to this maximum dimension. The antenna has an omnidirectional radiation pattern in the horizontal plane, with maximum radiation and reception in the horizontal plane, decreasing radiation and reception with increasing angle away from the horizontal plane, and substantially zero radiation and reception vertically. t will be understood, of course, that, while the forms of the invention herein shown and described constitute preferred embodiments, it is not intended herein to illustrate all of the possible equivalent forms or ramifications of the invention. It will also be understood that the words used are words of description rather than of limitation, and that various changes may be made without departing from the spirit or scope of the invention herein disclosed.

What is claimed is:

1. An antenna comprising: a plurality of conductors; each said conductor formed in a substantially circular loop; said loops having equal diameters and being dis posed with a diameter of each loop substantially coinciding with a diameter of each of the other loops and with the planes of said loops disposed around said common diameter at equal angles to the planes of adjacent loops; alternate loops, forming a first group, being connected together at one end of said common diameter; the remaining alternate loops, forming a second group, being connected together at the opposite end of said common diameter; first conducting means connected to the common connection of said first group of alternate loops; and second conducting means connected to the common connection of said second group of alternate loops.

2. An antenna according to claim 1, in which said first conducting means comprises the outer conductor of a coaxial cable, said outer conductor terminating at said common connection of said first group of loops, and in which said second conducting means comprises a monopole connected to the inner conductor of said coaxial cable, said monopole extending along said common diameter to said common connection of said second loops.

3. An antenna according to claim 2, in which the diamgroup of eter of each said loop is approximately one-quarter wave opole vertically positioned to provide maximum radiationv in a horizontal plane, decreasing radiation with increasing angle above or below said horizontal plane, and substantially zero radiation in the vertical direction.

6. An antenna according to claim 3, having said monopole vertically positioned to provide substantially uniform radiation and reception in any horizontaldirection and to provide maximum radiation and reception in a horizontal plane, decreasing radiation and reception with increasing angle above or below said horizontal plane, and substantially zero radiation and reception in the vertical direction.

7. An antenna comprising: a plurality of conductors; each said conductor formed in a substantially circular loop; said loops having equal diameters and being disposed With a diameter of each loop substantially coinciding with a diameter of each of the other loops and with the planes of said loops disposed around said common diameter at equal angles to the planes of adjacent loops; alternate loops, forming a first group, being connected together at one end of said common diameter; each half of each loop in said first group being insulated from the other half of the same loop, and from the other loops, at the end of said common diameteropposite the end at which said loops of said first group are connected together; the remaining alternate loops, forming a second group, being connected together at the opposite end of said common diameter; each half of each loop in said second group being insulated from the other half of the same loop, and from the other loops, at the end of said common diameter opposite the end at which said loops of said second group are connected together; first conducting means connected to the common connection oi said first group of alternate'loops; and second conducting means connected to the common connection of said second group of alternate loops.

8. An antenna comprising: a plurality of conductors; each said conductor formed in a substantially circular loop; said loops having equal diameters and being disposed with a diameter of each loop substantially coinciding with a diameter of each of the other loops and with the planes of said loops disposed around said common diameter at equal angles to the planes of adjacent loops; alternate loops, forming a first group, being connected together at one end of said common diameter; the remaining alternate loops, forming a second group, being connected together at the opposite end of said common diameter; each said loop being a continuous circular member; and the loops of said first group being insulated from the loops of said second group.

9. An antenna according to claim 8, in which the loops of said first group are connected together at each end of said common diameter and in which the loops of said second group are connected together at each end of said common diameter.

Moloney Feb. 28, 1928 Neinfeldt Apr. 8, 1930